@article{adamo_1999a, title = {Toward Reliable Density Functional Methods without Adjustable Parameters: {{The PBE0}} Model}, shorttitle = {Toward Reliable Density Functional Methods without Adjustable Parameters}, author = {Adamo, Carlo and Barone, Vincenzo}, year = {1999}, month = apr, journal = {J. Chem. Phys.}, volume = {110}, number = {13}, pages = {6158--6170}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.478522}, file = {/Users/monino/Zotero/storage/EHYRIT8T/Adamo et Barone - 1999 - Toward reliable density functional methods without.pdf} } @article{andersson_1990, title = {Second-Order Perturbation Theory with a {{CASSCF}} Reference Function}, author = {Andersson, Kerstin. and Malmqvist, Per Aake. and Roos, Bjoern O. and Sadlej, Andrzej J. and Wolinski, Krzysztof.}, year = {1990}, month = jul, journal = {J. Phys. Chem.}, volume = {94}, number = {14}, pages = {5483--5488}, publisher = {{American Chemical Society}}, issn = {0022-3654}, doi = {10.1021/j100377a012}, file = {/Users/monino/Zotero/storage/5LW6PKJ9/Andersson et al. - 1990 - Second-order perturbation theory with a CASSCF ref.pdf;/Users/monino/Zotero/storage/VXS655QG/j100377a012.html} } @article{angeli_2001, title = {N-Electron Valence State Perturbation Theory: A Fast Implementation of the Strongly Contracted Variant}, shorttitle = {N-Electron Valence State Perturbation Theory}, author = {Angeli, Celestino and Cimiraglia, Renzo and Malrieu, Jean-Paul}, year = {2001}, month = dec, journal = {Chemical Physics Letters}, volume = {350}, number = {3}, pages = {297--305}, issn = {0009-2614}, doi = {10.1016/S0009-2614(01)01303-3}, abstract = {In this work we reconsider the strongly contracted variant of the n-electron valence state perturbation theory (SC NEV-PT) which uses Dyall's Hamiltonian to define the zero-order energies (SC NEV-PT(D)). We develop a formalism in which the key quantities used for the second-order perturbation correction to the energy are written in terms of the matrix elements of suitable operators evaluated on the zero-order wavefunction, without the explicit knowledge of the perturbation functions. The new formalism strongly improves the computation performances. As test cases we present two preliminary studies: (a) on N2 where the convergence of the spectroscopic properties as a function of the basis set and CAS-CI space is discussed and (b) on Cr2 where it is shown that the SC NEV-PT(D) method is able to provide the correct profile for the potential energy curve.}, langid = {english}, file = {/Users/monino/Zotero/storage/MU8H53BC/Angeli et al. - 2001 - N-electron valence state perturbation theory a fa.pdf;/Users/monino/Zotero/storage/KW4GRB2F/S0009261401013033.html} } @article{angeli_2001a, title = {Introduction of N-Electron Valence States for Multireference Perturbation Theory}, author = {Angeli, C. and Cimiraglia, R. and Evangelisti, S. and Leininger, T. and Malrieu, J.-P.}, year = {2001}, month = jun, journal = {J. Chem. Phys.}, volume = {114}, number = {23}, pages = {10252--10264}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.1361246}, file = {/Users/monino/Zotero/storage/LXLLFJXM/Angeli et al. - 2001 - Introduction of n-electron valence states for mult.pdf} } @article{angeli_2002, title = {N-Electron Valence State Perturbation Theory: {{A}} Spinless Formulation and an Efficient Implementation of the Strongly Contracted and of the Partially Contracted Variants}, shorttitle = {N-Electron Valence State Perturbation Theory}, author = {Angeli, Celestino and Cimiraglia, Renzo and Malrieu, Jean-Paul}, year = {2002}, month = nov, journal = {J. Chem. Phys.}, volume = {117}, number = {20}, pages = {9138--9153}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.1515317}, file = {/Users/monino/Zotero/storage/HHFA46GF/Angeli et al. - 2002 - n-electron valence state perturbation theory A sp.pdf;/Users/monino/Zotero/storage/CPKUV9TE/1.html} } @article{baeyer_1885, title = {Ueber {{Polyacetylenverbindungen}}}, author = {Baeyer, Adolf}, year = {1885}, journal = {Berichte Dtsch. Chem. Ges.}, volume = {18}, number = {2}, pages = {2269--2281}, issn = {1099-0682}, doi = {10.1002/cber.18850180296}, copyright = {Copyright \textcopyright{} 1885 WILEY-VCH Verlag GmbH \& Co. KGaA, Weinheim}, langid = {english}, annotation = {\_eprint: https://chemistry-europe.onlinelibrary.wiley.com/doi/pdf/10.1002/cber.18850180296}, file = {/Users/monino/Zotero/storage/T9A8FP8V/Baeyer - 1885 - Ueber Polyacetylenverbindungen.pdf;/Users/monino/Zotero/storage/B56CA56Z/cber.html} } @article{balkova_1994, title = {A Multireference Coupled-cluster Study of the Ground State and Lowest Excited States of Cyclobutadiene}, author = {Balkov{\'a}, A. and Bartlett, Rodney J.}, year = {1994}, month = aug, journal = {J. Chem. Phys.}, volume = {101}, number = {10}, pages = {8972}, publisher = {{American Institute of PhysicsAIP}}, issn = {0021-9606}, doi = {10.1063/1.468025}, abstract = {The electronic structure of the ground state and several low-lying excited states of cyclobutadiene are studied using the new state-universal multireference coupled-cluster method with single and double excitations (MR-CCSD) augmented by a noniterative inclusion of the triple excitations [MR-CCSD(T)]. Two possible ground state configurations are examined, namely the square and the distorted rectangular geometries, and the multireference coupled-cluster energy barrier for the interconversion between the two rectangular ground state structures is estimated to be 6.6 kcal mol-1 compared with the best theoretical value, 6.4 kcal mol-1 obtained using the highly accurate coupled-cluster method with full inclusion of the triple excitations (CCSDT). The ordering of electronic states for the square geometry is determined, with the ground state singlet being located 6.9 kcal mol-1 below the lowest triplet electronic state. We also examine the potential energy surface for the interconversion between the two equivalent second-order Jahn\textendash Teller rhombic structures for the first excited singlet state. When comparing the MRCC energies with the results provided by various single- and multireference correlation methods, the critical importance of including both the dynamic and nondynamic correlation for a qualitatively correct description of the electronic structure of cyclobutadiene is emphasized. We also address the invariance properties of the present MRCC methods with respect to the alternative selections of reference orbital spaces.}, copyright = {\textcopyright{} 1994 American Institute of Physics.}, langid = {english}, file = {/Users/monino/Zotero/storage/6MCJDAMM/1.html} } @article{bally_1980, title = {Cyclobutadiene}, author = {Bally, Thomas and Masamune, Satoru}, year = {1980}, month = jan, journal = {Tetrahedron}, volume = {36}, number = {3}, pages = {343--370}, issn = {0040-4020}, doi = {10.1016/0040-4020(80)87003-7}, langid = {english}, file = {/Users/monino/Zotero/storage/DXWL3L8N/Bally et Masamune - 1980 - Cyclobutadiene.pdf;/Users/monino/Zotero/storage/XQ98S2QN/0040402080870037.html} } @article{banerjee_2016, title = {A State-Specific Multi-Reference Coupled-Cluster Approach with a Cost-Effective Treatment of Connected Triples: Implementation to Geometry Optimisation}, shorttitle = {A State-Specific Multi-Reference Coupled-Cluster Approach with a Cost-Effective Treatment of Connected Triples}, author = {Banerjee, Debi and Mondal, Monosij and Chattopadhyay, Sudip and Mahapatra, Uttam Sinha}, year = {2016}, month = may, journal = {Mol. Phys.}, volume = {114}, number = {10}, pages = {1591--1608}, publisher = {{Taylor \& Francis}}, issn = {0026-8976}, doi = {10.1080/00268976.2016.1142126}, abstract = {Recently, we have suggested an approximate state-specific multi-reference coupled-cluster (SS-MRCC) singles, doubles and triples method based on the CCSDT-1a+d approximation applied to the single-reference CC approach, in which the contribution of the connected triple excitations is iteratively treated. The method, abbreviated as SS-MRCCSDT-1a+d is intruder-free and fully size-extensive. It has been employed for geometry optimisations of various systems possessing quasi-degeneracy of varying degrees (like N2H2 and O3) by invoking numerical gradient scheme. The method is also applied to CH2 and square cyclobutadiene in their excited states. For all systems under study, the computed values are in good accordance with state-of-the-art theoretical estimates indicating that the method might be a promising candidate for an accurate treatment of geometrical parameters of states plagued by electronic degeneracy in a computationally tractable manner.}, annotation = {\_eprint: https://doi.org/10.1080/00268976.2016.1142126}, file = {/Users/monino/Zotero/storage/W9FBB4VK/00268976.2016.html} } @article{becke_1988b, title = {Density-Functional Exchange-Energy Approximation with Correct Asymptotic Behavior}, author = {Becke, A. D.}, year = {1988}, month = sep, journal = {Phys. Rev. A}, volume = {38}, number = {6}, pages = {3098--3100}, publisher = {{American Physical Society}}, doi = {10.1103/PhysRevA.38.3098}, abstract = {Current gradient-corrected density-functional approximations for the exchange energies of atomic and molecular systems fail to reproduce the correct 1/r asymptotic behavior of the exchange-energy density. Here we report a gradient-corrected exchange-energy functional with the proper asymptotic limit. Our functional, containing only one parameter, fits the exact Hartree-Fock exchange energies of a wide variety of atomic systems with remarkable accuracy, surpassing the performance of previous functionals containing two parameters or more., This article appears in the following collection:}, file = {/Users/monino/Zotero/storage/HYTWLA6W/Becke - 1988 - Density-functional exchange-energy approximation w.pdf;/Users/monino/Zotero/storage/8JN8MYC2/PhysRevA.38.html} } @article{becke_1993b, title = {Density-functional Thermochemistry. {{III}}. {{The}} Role of Exact Exchange}, author = {Becke, Axel D.}, year = {1993}, month = apr, journal = {J. Chem. Phys.}, volume = {98}, number = {7}, pages = {5648--5652}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.464913} } @article{casanova_2020, title = {Spin-Flip Methods in Quantum Chemistry}, author = {Casanova, David and Krylov, Anna I.}, year = {2020}, month = feb, journal = {Phys. Chem. Chem. Phys.}, volume = {22}, number = {8}, pages = {4326--4342}, publisher = {{The Royal Society of Chemistry}}, issn = {1463-9084}, doi = {10.1039/C9CP06507E}, abstract = {This Perspective discusses salient features of the spin-flip approach to strong correlation and describes different methods that sprung from this idea. The spin-flip treatment exploits the different physics of low-spin and high-spin states and is based on the observation that correlation is small for same-spin electrons. By using a well-behaved high-spin state as a reference, one can access problematic low-spin states by deploying the same formal tools as in the excited-state treatments (i.e., linear response, propagator, or equation-of-motion theories). The Perspective reviews applications of this strategy within wave function and density functional theory frameworks as well as the extensions for molecular properties and spectroscopy. The utility of spin-flip methods is illustrated by examples. Limitations and proposed future directions are also discussed.}, langid = {english}, file = {/Users/monino/Zotero/storage/7E3MQEQM/Casanova et Krylov - 2020 - Spin-flip methods in quantum chemistry.pdf} } @article{christiansen_1995, title = {Response Functions in the {{CC3}} Iterative Triple Excitation Model}, author = {Christiansen, Ove and Koch, Henrik and Jo/rgensen, Poul}, year = {1995}, month = nov, journal = {J. Chem. Phys.}, volume = {103}, number = {17}, pages = {7429--7441}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.470315} } @article{dunning_1989, title = {Gaussian Basis Sets for Use in Correlated Molecular Calculations. {{I}}. {{The}} Atoms Boron through Neon and Hydrogen}, author = {Dunning, Thom H.}, year = {1989}, month = jan, journal = {J. Chem. Phys.}, volume = {90}, number = {2}, pages = {1007--1023}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.456153} } @article{eckert-maksic_2006, title = {Automerization Reaction of Cyclobutadiene and Its Barrier Height: {{An}} Ab Initio Benchmark Multireference Average-Quadratic Coupled Cluster Study}, shorttitle = {Automerization Reaction of Cyclobutadiene and Its Barrier Height}, author = {{Eckert-Maksi{\'c}}, Mirjana and Vazdar, Mario and Barbatti, Mario and Lischka, Hans and Maksi{\'c}, Zvonimir B.}, year = {2006}, month = aug, journal = {J. Chem. Phys.}, volume = {125}, number = {6}, pages = {064310}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.2222366}, abstract = {The problem of the double bond flipping interconversion of the two equivalent ground state structures of cyclobutadiene (CBD) is addressed at the multireference average-quadratic coupled cluster level of theory, which is capable of optimizing the structural parameters of the ground, transition, and excited states on an equal footing. The barrier height involving both the electronic and zero-point vibrational energy contributions is 6.3kcalmol-16.3kcalmol-1{$<$}math display="inline" overflow="scroll" altimg="eq-00001.gif"{$><$}mrow{$><$}mn{$>$}6.3{$<$}/mn{$><$}mspace width="0.3em"{$><$}/mspace{$><$}mi{$>$}kcal{$<$}/mi{$><$}mspace width="0.2em"{$><$}/mspace{$><$}msup{$><$}mi{$>$}mol{$<$}/mi{$><$}mrow{$><$}mo{$>-<$}/mo{$><$}mn{$>$}1{$<$}/mn{$><$}/mrow{$><$}/msup{$><$}/mrow{$><$}/math{$>$}, which is higher than the best earlier theoretical estimate of 4.0kcalmol-14.0kcalmol-1{$<$}math display="inline" overflow="scroll" altimg="eq-00002.gif"{$><$}mrow{$><$}mn{$>$}4.0{$<$}/mn{$><$}mspace width="0.3em"{$><$}/mspace{$><$}mi{$>$}kcal{$<$}/mi{$><$}mspace width="0.2em"{$><$}/mspace{$><$}msup{$><$}mi{$>$}mol{$<$}/mi{$><$}mrow{$><$}mo{$>-<$}/mo{$><$}mn{$>$}1{$<$}/mn{$><$}/mrow{$><$}/msup{$><$}/mrow{$><$}/math{$>$}. This result is confirmed by including into the reference space the orbitals of the CC {$\sigma\sigma<$}math display="inline" overflow="scroll" altimg="eq-00003.gif"{$><$}mi{$>\sigma<$}/mi{$><$}/math{$>$} bonds beyond the standard {$\pi\pi<$}math display="inline" overflow="scroll" altimg="eq-00004.gif"{$><$}mi{$>\pi<$}/mi{$><$}/math{$>$} orbital space. It places the present value into the middle of the range of the measured data (1.6\textendash 10kcalmol-1)(1.6\textendash 10kcalmol-1){$<$}math display="inline" overflow="scroll" altimg="eq-00005.gif"{$><$}mrow{$><$}mo{$>$}({$<$}/mo{$><$}mn{$>$}1.6{$<$}/mn{$><$}mo{$>$}\textendash{$<$}/mo{$><$}mn{$>$}10{$<$}/mn{$><$}mspace width="0.3em"{$><$}/mspace{$><$}mi{$>$}kcal{$<$}/mi{$><$}mspace width="0.2em"{$><$}/mspace{$><$}msup{$><$}mi{$>$}mol{$<$}/mi{$><$}mrow{$><$}mo{$>-<$}/mo{$><$}mn{$>$}1{$<$}/mn{$><$}/mrow{$><$}/msup{$><$}mo{$>$}){$<$}/mo{$><$}/mrow{$><$}/math{$>$}. An adiabatic singlet-triplet energy gap of 7.4kcalmol-17.4kcalmol-1{$<$}math display="inline" overflow="scroll" altimg="eq-00006.gif"{$><$}mrow{$><$}mn{$>$}7.4{$<$}/mn{$><$}mspace width="0.3em"{$><$}/mspace{$><$}mi{$>$}kcal{$<$}/mi{$><$}mspace width="0.2em"{$><$}/mspace{$><$}msup{$><$}mi{$>$}mol{$<$}/mi{$><$}mrow{$><$}mo{$>-<$}/mo{$><$}mn{$>$}1{$<$}/mn{$><$}/mrow{$><$}/msup{$><$}/mrow{$><$}/math{$>$} between the transition state Btg1Btg1{$<$}math display="inline" overflow="scroll" altimg="eq-00007.gif"{$><$}mmultiscripts{$><$}mi{$>$}B{$<$}/mi{$><$}mrow{$><$}mi{$>$}t{$<$}/mi{$><$}mi{$>$}g{$<$}/mi{$><$}/mrow{$><$}none{$><$}/none{$><$}mprescripts{$><$}/mprescripts{$><$}none{$><$}/none{$><$}mn{$>$}1{$<$}/mn{$><$}/mmultiscripts{$><$}/math{$>$} and the first triplet A2g3A2g3{$<$}math display="inline" overflow="scroll" altimg="eq-00008.gif"{$><$}mmultiscripts{$><$}mi{$>$}A{$<$}/mi{$><$}mrow{$><$}mn{$>$}2{$<$}/mn{$><$}mi{$>$}g{$<$}/mi{$><$}/mrow{$><$}none{$><$}/none{$><$}mprescripts{$><$}/mprescripts{$><$}none{$><$}/none{$><$}mn{$>$}3{$<$}/mn{$><$}/mmultiscripts{$><$}/math{$>$} state is obtained. A low barrier height for the CBD automerization and a small {$\Delta$}E(A2g3,B1g1){$\Delta$}E(A2g3,B1g1){$<$}math display="inline" overflow="scroll" altimg="eq-00009.gif"{$><$}mrow{$><$}mi{$>\Delta<$}/mi{$><$}mi{$>$}E{$<$}/mi{$><$}mrow{$><$}mo{$>$}({$<$}/mo{$><$}mmultiscripts{$><$}mi{$>$}A{$<$}/mi{$><$}mrow{$><$}mn{$>$}2{$<$}/mn{$><$}mi{$>$}g{$<$}/mi{$><$}/mrow{$><$}none{$><$}/none{$><$}mprescripts{$><$}/mprescripts{$><$}none{$><$}/none{$><$}mn{$>$}3{$<$}/mn{$><$}/mmultiscripts{$><$}mo{$>$},{$<$}/mo{$><$}mmultiscripts{$><$}mi{$>$}B{$<$}/mi{$><$}mrow{$><$}mn{$>$}1{$<$}/mn{$><$}mi{$>$}g{$<$}/mi{$><$}/mrow{$><$}none{$><$}/none{$><$}mprescripts{$><$}/mprescripts{$><$}none{$><$}/none{$><$}mn{$>$}1{$<$}/mn{$><$}/mmultiscripts{$><$}mo{$>$}){$<$}/mo{$><$}/mrow{$><$}/mrow{$><$}/math{$>$} gap bear some relevance on the highly pronounced reactivity of CBD, which is briefly discussed.}, file = {/Users/monino/Zotero/storage/F5Y4YKWD/Eckert-Maksić et al. - 2006 - Automerization reaction of cyclobutadiene and its .pdf;/Users/monino/Zotero/storage/SSRES9DP/1.html} } @article{ermer_1983, title = {Three {{Arguments Supporting}} a {{Rectangular Structure}} for {{Tetra-tert-butylcyclobutadiene}}}, author = {Ermer, Otto and Heilbronner, Edgar}, year = {1983}, journal = {Angew. Chem. Int. Ed. Engl.}, volume = {22}, number = {5}, pages = {402--403}, issn = {1521-3773}, doi = {10.1002/anie.198304021}, copyright = {Copyright \textcopyright{} 1983 by Verlag Chemie, GmbH, Germany}, langid = {english}, annotation = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.198304021}, file = {/Users/monino/Zotero/storage/T32BDQPQ/Ermer et Heilbronner - 1983 - Three Arguments Supporting a Rectangular Structure.pdf;/Users/monino/Zotero/storage/4BR2A634/anie.html} } @article{ernzerhof_1999, title = {Assessment of the {{Perdew}}\textendash{{Burke}}\textendash{{Ernzerhof}} Exchange-Correlation Functional}, author = {Ernzerhof, Matthias and Scuseria, Gustavo E.}, year = {1999}, month = mar, journal = {J. Chem. Phys.}, volume = {110}, number = {11}, pages = {5029--5036}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.478401}, file = {/Users/monino/Zotero/storage/KI5Z4SJW/Ernzerhof et Scuseria - 1999 - Assessment of the Perdew–Burke–Ernzerhof exchange-.pdf} } @article{fantuzzi_2016, title = {The {{Nature}} of the {{Singlet}} and {{Triplet States}} of {{Cyclobutadiene}} as {{Revealed}} by {{Quantum Interference}}}, author = {Fantuzzi, Felipe and Cardozo, Thiago M. and Nascimento, Marco A. C.}, year = {2016}, journal = {ChemPhysChem}, volume = {17}, number = {2}, pages = {288--295}, issn = {1439-7641}, doi = {10.1002/cphc.201500885}, abstract = {The generalized product function energy partitioning (GPF-EP) method is applied to the description of the cyclobutadiene molecule. The GPF wave function was built to reproduce generalized valence bond (GVB) and spin-coupled (SC) wave functions. The influence of quasiclassical and quantum interference contributions to each chemical bond of the system are analyzed along the automerization reaction coordinate for the lowest singlet and triplet states. The results show that the interference effect on the {$\pi$} space reduces the electronic energy of the singlet cyclobutadiene relative to the second-order Jahn\textendash Teller distortion, which takes the molecule from a D4h to a D2h structure. Our results also suggest that the {$\pi$} space of the 1B1g state of the square cyclobutadiene is composed of a weak four center\textendash four electron bond, whereas the 3A2g state has a four center\textendash two electron {$\pi$} bond. Finally, we also show that, although strain effects are nonnegligible, the thermodynamics of the main decomposition pathway of cyclobutadiene in the gas phase is dominated by the {$\pi$} space interference.}, langid = {english}, annotation = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/cphc.201500885}, file = {/Users/monino/Zotero/storage/NTSYBUS7/Fantuzzi et al. - 2016 - The Nature of the Singlet and Triplet States of Cy.pdf;/Users/monino/Zotero/storage/C7HBJB3Y/cphc.html} } @article{garniron_2019, title = {Quantum {{Package}} 2.0: {{An Open-Source Determinant-Driven Suite}} of {{Programs}}}, shorttitle = {Quantum {{Package}} 2.0}, author = {Garniron, Yann and Applencourt, Thomas and Gasperich, Kevin and Benali, Anouar and Fert{\'e}, Anthony and Paquier, Julien and Pradines, Barth{\'e}l{\'e}my and Assaraf, Roland and Reinhardt, Peter and Toulouse, Julien and Barbaresco, Pierrette and Renon, Nicolas and David, Gr{\'e}goire and Malrieu, Jean-Paul and V{\'e}ril, Micka{\"e}l and Caffarel, Michel and Loos, Pierre-Fran{\c c}ois and Giner, Emmanuel and Scemama, Anthony}, year = {2019}, month = jun, journal = {J. Chem. Theory Comput.}, volume = {15}, number = {6}, pages = {3591--3609}, publisher = {{American Chemical Society}}, issn = {1549-9618}, doi = {10.1021/acs.jctc.9b00176}, abstract = {Quantum chemistry is a discipline which relies heavily on very expensive numerical computations. The scaling of correlated wave function methods lies, in their standard implementation, between O(N5) and O(eN), where N is proportional to the system size. Therefore, performing accurate calculations on chemically meaningful systems requires (i) approximations that can lower the computational scaling and (ii) efficient implementations that take advantage of modern massively parallel architectures. Quantum Package is an open-source programming environment for quantum chemistry specially designed for wave function methods. Its main goal is the development of determinant-driven selected configuration interaction (sCI) methods and multireference second-order perturbation theory (PT2). The determinant-driven framework allows the programmer to include any arbitrary set of determinants in the reference space, hence providing greater methodological freedom. The sCI method implemented in Quantum Package is based on the CIPSI (Configuration Interaction using a Perturbative Selection made Iteratively) algorithm which complements the variational sCI energy with a PT2 correction. Additional external plugins have been recently added to perform calculations with multireference coupled cluster theory and range-separated density-functional theory. All the programs are developed with the IRPF90 code generator, which simplifies collaborative work and the development of new features. Quantum Package strives to allow easy implementation and experimentation of new methods, while making parallel computation as simple and efficient as possible on modern supercomputer architectures. Currently, the code enables, routinely, to realize runs on roughly 2 000 CPU cores, with tens of millions of determinants in the reference space. Moreover, we have been able to push up to 12 288 cores in order to test its parallel efficiency. In the present manuscript, we also introduce some key new developments: (i) a renormalized second-order perturbative correction for efficient extrapolation to the full CI limit and (ii) a stochastic version of the CIPSI selection performed simultaneously to the PT2 calculation at no extra cost.}, file = {/Users/monino/Zotero/storage/I2Q5L62K/Garniron et al. - 2019 - Quantum Package 2.0 An Open-Source Determinant-Dr.pdf} } @article{hirata_2000, title = {High-Order Determinantal Equation-of-Motion Coupled-Cluster Calculations for Electronic Excited States}, author = {Hirata, So and Nooijen, Marcel and Bartlett, Rodney J.}, year = {2000}, month = aug, journal = {Chemical Physics Letters}, volume = {326}, number = {3}, pages = {255--262}, issn = {0009-2614}, doi = {10.1016/S0009-2614(00)00772-7}, abstract = {A general-order equation-of-motion coupled-cluster (EOM-CC) method, which is capable of computing the excitation energies of molecules at any given pair of orders (m and n) of the cluster operator and the linear excitation operator, is developed by employing a determinantal algorithm. The EOM-CC(m,n) results of the vertical excitation energies are presented for CH+ with m and n varied independently in the range of 1{$\leqslant$}m,n{$\leqslant$}4 and for CH2 with 1{$\leqslant$}m=n{$\leqslant$}6. EOM-CCSDT [EOM-CC(3,3)] provides the excitation energies that are within 0.1 eV of the full configuration interaction results for dominant double replacement transitions.}, langid = {english}, file = {/Users/monino/Zotero/storage/ZZI4JPPT/Hirata et al. - 2000 - High-order determinantal equation-of-motion couple.pdf} } @article{hirata_2004, title = {Higher-Order Equation-of-Motion Coupled-Cluster Methods}, author = {Hirata, So}, year = {2004}, month = jul, journal = {J. Chem. Phys.}, volume = {121}, number = {1}, pages = {51--59}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.1753556}, file = {/Users/monino/Zotero/storage/3HCJINRI/Hirata - 2004 - Higher-order equation-of-motion coupled-cluster me.pdf} } @article{irngartinger_1983, title = {Bonding {{Electron Density Distribution}} in {{Tetra-tert-butylcyclobutadiene}}\textemdash{} {{A Molecule}} with an {{Obviously Non-Square Four-Membered}} Ring}, author = {Irngartinger, Hermann and Nixdorf, Matthias}, year = {1983}, journal = {Angew. Chem. Int. Ed. Engl.}, volume = {22}, number = {5}, pages = {403--404}, issn = {1521-3773}, doi = {10.1002/anie.198304031}, copyright = {Copyright \textcopyright{} 1983 by Verlag Chemie, GmbH, Germany}, langid = {english}, annotation = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.198304031}, file = {/Users/monino/Zotero/storage/QZP8JWNP/Irngartinger et Nixdorf - 1983 - Bonding Electron Density Distribution in Tetra-ter.pdf;/Users/monino/Zotero/storage/X5NU6NTT/anie.html} } @article{kallay_2004, title = {Calculation of Excited-State Properties Using General Coupled-Cluster and Configuration-Interaction Models}, author = {K{\'a}llay, Mih{\'a}ly and Gauss, J{\"u}rgen}, year = {2004}, month = nov, journal = {J. Chem. Phys.}, volume = {121}, number = {19}, pages = {9257--9269}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.1805494}, file = {/Users/monino/Zotero/storage/TEHKUF6P/Kállay et Gauss - 2004 - Calculation of excited-state properties using gene.pdf} } @article{karadakov_2008, title = {Ground- and {{Excited-State Aromaticity}} and {{Antiaromaticity}} in {{Benzene}} and {{Cyclobutadiene}}}, author = {Karadakov, Peter B.}, year = {2008}, month = aug, journal = {J. Phys. Chem. A}, volume = {112}, number = {31}, pages = {7303--7309}, publisher = {{American Chemical Society}}, issn = {1089-5639}, doi = {10.1021/jp8037335}, abstract = {The aromaticity and antiaromaticity of the ground state (S0), lowest triplet state (T1), and first singlet excited state (S1) of benzene, and the ground states (S0), lowest triplet states (T1), and the first and second singlet excited states (S1 and S2) of square and rectangular cyclobutadiene are assessed using various magnetic criteria including nucleus-independent chemical shifts (NICS), proton shieldings, and magnetic susceptibilities calculated using complete-active-space self-consistent field (CASSCF) wave functions constructed from gauge-including atomic orbitals (GIAOs). These magnetic criteria strongly suggest that, in contrast to the well-known aromaticity of the S0 state of benzene, the T1 and S1 states of this molecule are antiaromatic. In square cyclobutadiene, which is shown to be considerably more antiaromatic than rectangular cyclobutadiene, the magnetic properties of the T1 and S1 states allow these to be classified as aromatic. According to the computed magnetic criteria, the T1 state of rectangular cyclobutadiene is still aromatic, but the S1 state is antiaromatic, just as the S2 state of square cyclobutadiene; the S2 state of rectangular cyclobutadiene is nonaromatic. The results demonstrate that the well-known ``triplet aromaticity'' of cyclic conjugated hydrocarbons represents a particular case of a broader concept of excited-state aromaticity and antiaromaticity. It is shown that while electronic excitation may lead to increased nuclear shieldings in certain low-lying electronic states, in general its main effect can be expected to be nuclear deshielding, which can be substantial for heavier nuclei.}, file = {/Users/monino/Zotero/storage/7UMPEAYT/Karadakov - 2008 - Ground- and Excited-State Aromaticity and Antiarom.pdf;/Users/monino/Zotero/storage/7ULNL76P/jp8037335.html} } @article{koch_1997, title = {The {{CC3}} Model: {{An}} Iterative Coupled Cluster Approach Including Connected Triples}, shorttitle = {The {{CC3}} Model}, author = {Koch, Henrik and Christiansen, Ove and Jo/rgensen, Poul and {Sanchez de Mer{\'a}s}, Alfredo M. and Helgaker, Trygve}, year = {1997}, month = feb, journal = {J. Chem. Phys.}, volume = {106}, number = {5}, pages = {1808--1818}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.473322}, file = {/Users/monino/Zotero/storage/BEW2ATM3/Koch et al. - 1997 - The CC3 model An iterative coupled cluster approa.pdf} } @article{kostenko_2017, title = {Spectroscopic {{Observation}} of the {{Triplet Diradical State}} of a {{Cyclobutadiene}}}, author = {Kostenko, Arseni and Tumanskii, Boris and Kobayashi, Yuzuru and Nakamoto, Masaaki and Sekiguchi, Akira and Apeloig, Yitzhak}, year = {2017}, journal = {Angew. Chem. Int. Ed.}, volume = {56}, number = {34}, pages = {10183--10187}, issn = {1521-3773}, doi = {10.1002/anie.201705228}, abstract = {Tetrakis(trimethylsilyl)cyclobuta-1,3-diene (1) was subjected to a temperature-dependent EPR study to allow the first spectroscopic observation of a triplet diradical state of a cyclobutadiene (2). From the temperature dependent EPR absorption area we derive a singlet\textrightarrow triplet (1\textrightarrow 2) energy gap, EST, of 13.9 kcal mol-1, in agreement with calculated values. The zero-field splitting parameters D=0.171 cm-1, E=0 cm-1 are accurately reproduced by DFT calculations. The triplet diradical 2 is thermally accessible at moderate temperatures. It is not an intermediate in the thermal cycloreversion of cyclobutadiene to two acetylene molecules.}, langid = {english}, annotation = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/anie.201705228}, file = {/Users/monino/Zotero/storage/IKNKPNI3/anie.html} } @article{kreile_1986, title = {Uv Photoelectron Spectrum of Cyclobutadiene. Free Cyclobutadiene Stable up to High Temperatures}, author = {Kreile, J{\"u}rgen and M{\"u}nzel, Norbert and Schweig, Armin and Specht, Harald}, year = {1986}, month = feb, journal = {Chemical Physics Letters}, volume = {124}, number = {2}, pages = {140--146}, issn = {0009-2614}, doi = {10.1016/0009-2614(86)85133-8}, abstract = {The Hel photoelectron spectrum of cyclobutadiene (CB) has been obtained under conditions which demonstrate that free CB is stable up to temperatures of several hundred \textdegree C. A new experimental argument for the rectangular geometry of CB is presented. Shake-up structures are unimportant for the interpretation of the PE spectrum of CB. LNDO/S PERTCI, MNDO PERTCI and previous experimental vertical ionization energy estimates accord with the experimental data.}, langid = {english}, file = {/Users/monino/Zotero/storage/2EQ8LH4G/Kreile et al. - 1986 - Uv photoelectron spectrum of cyclobutadiene. free .pdf;/Users/monino/Zotero/storage/QHJZT5VV/0009261486851338.html} } @article{kucharski_1991, title = {Recursive Intermediate Factorization and Complete Computational Linearization of the Coupled-Cluster Single, Double, Triple, and Quadruple Excitation Equations}, author = {Kucharski, Stanislaw A. and Bartlett, Rodney J.}, year = {1991}, month = jul, journal = {Theoret. Chim. Acta}, volume = {80}, number = {4}, pages = {387--405}, issn = {1432-2234}, doi = {10.1007/BF01117419}, abstract = {The nonlinear CCSDTQ equations are written in a fully linearized form, via the introduction of computationally convenient intermediates. An efficient formulation of the coupled cluster method is proposed. Due to a recursive method for the calculation of intermediates, all computational steps involve the multiplication of an intermediate with aT vertex. This property makes it possible to express the CC equations exclusively in terms of matrix products which can be directly transformed into a highly vectorized program.}, langid = {english}, file = {/Users/monino/Zotero/storage/L3VLAU8A/Kucharski et Bartlett - 1991 - Recursive intermediate factorization and complete .pdf} } @article{lee_1988a, title = {Development of the {{Colle-Salvetti}} Correlation-Energy Formula into a Functional of the Electron Density}, author = {Lee, Chengteh and Yang, Weitao and Parr, Robert G.}, year = {1988}, month = jan, journal = {Phys. Rev. B}, volume = {37}, number = {2}, pages = {785--789}, publisher = {{American Physical Society}}, doi = {10.1103/PhysRevB.37.785}, abstract = {A correlation-energy formula due to Colle and Salvetti [Theor. Chim. Acta 37, 329 (1975)], in which the correlation energy density is expressed in terms of the electron density and a Laplacian of the second-order Hartree-Fock density matrix, is restated as a formula involving the density and local kinetic-energy density. On insertion of gradient expansions for the local kinetic-energy density, density-functional formulas for the correlation energy and correlation potential are then obtained. Through numerical calculations on a number of atoms, positive ions, and molecules, of both open- and closed-shell type, it is demonstrated that these formulas, like the original Colle-Salvetti formulas, give correlation energies within a few percent., This article appears in the following collection:}, file = {/Users/monino/Zotero/storage/HXKK4EQ3/Lee et al. - 1988 - Development of the Colle-Salvetti correlation-ener.pdf;/Users/monino/Zotero/storage/CCMCH9PM/PhysRevB.37.html} } @article{lefrancois_2015, title = {Adapting Algebraic Diagrammatic Construction Schemes for the Polarization Propagator to Problems with Multi-Reference Electronic Ground States Exploiting the Spin-Flip Ansatz}, author = {Lefrancois, Daniel and Wormit, Michael and Dreuw, Andreas}, year = {2015}, month = sep, journal = {J. Chem. Phys.}, volume = {143}, number = {12}, pages = {124107}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.4931653}, abstract = {For the investigation of molecular systems with electronic ground states exhibiting multi-reference character, a spin-flip (SF) version of the algebraic diagrammatic construction (ADC) scheme for the polarization propagator up to third order perturbation theory (SF-ADC(3)) is derived via the intermediate state representation and implemented into our existing ADC computer program adcman. The accuracy of these new SF-ADC(n) approaches is tested on typical situations, in which the ground state acquires multi-reference character, like bond breaking of H2 and HF, the torsional motion of ethylene, and the excited states of rectangular and square-planar cyclobutadiene. Overall, the results of SF-ADC(n) reveal an accurate description of these systems in comparison with standard multi-reference methods. Thus, the spin-flip versions of ADC are easy-to-use methods for the calculation of ``few-reference'' systems, which possess a stable single-reference triplet ground state.}, file = {/Users/monino/Zotero/storage/2WIVTU65/Lefrancois et al. - 2015 - Adapting algebraic diagrammatic construction schem.pdf} } @article{levchenko_2004, title = {Equation-of-Motion Spin-Flip Coupled-Cluster Model with Single and Double Substitutions: {{Theory}} and Application to Cyclobutadiene}, shorttitle = {Equation-of-Motion Spin-Flip Coupled-Cluster Model with Single and Double Substitutions}, author = {Levchenko, Sergey V. and Krylov, Anna I.}, year = {2004}, month = jan, journal = {J. Chem. Phys.}, volume = {120}, number = {1}, pages = {175--185}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.1630018}, file = {/Users/monino/Zotero/storage/FDUTSFT8/Levchenko et Krylov - 2004 - Equation-of-motion spin-flip coupled-cluster model.pdf} } @article{li_2009, title = {Accounting for the Exact Degeneracy and Quasidegeneracy in the Automerization of Cyclobutadiene via Multireference Coupled-Cluster Methods}, author = {Li, Xiangzhu and Paldus, Josef}, year = {2009}, month = sep, journal = {J. Chem. Phys.}, volume = {131}, number = {11}, pages = {114103}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.3225203}, abstract = {The automerization of cyclobutadiene (CBD) is employed to test the performance of the reduced multireference (RMR) coupled-cluster (CC) method with singles and doubles (RMR CCSD) that employs a modest-size MR CISD wave function as an external source for the most important (primary) triples and quadruples in order to account for the nondynamic correlation effects in the presence of quasidegeneracy, as well as of its perturbatively corrected version accounting for the remaining (secondary) triples [RMR CCSD(T)]. The experimental results are compared with those obtained by the standard CCSD and CCSD(T) methods, by the state universal (SU) MR CCSD and its state selective or state specific (SS) version as formulated by Mukherjee et al. (SS MRCC or MkMRCC) and, wherever available, by the Brillouin\textendash Wigner MRCC [MR BWCCSD(T)] method. Both restricted Hartree-Fock (RHF) and multiconfigurational self-consistent field (MCSCF) molecular orbitals are employed. For a smaller STO-3G basis set we also make a comparison with the exact full configuration interaction (FCI) results. Both fundamental vibrational energies\textemdash as obtained via the integral averaging method (IAM) that can handle anomalous potentials and automatically accounts for anharmonicity\textendash{} and the CBD automerization barrier for the interconversion of the two rectangular structures are considered. It is shown that the RMR CCSD(T) potential has the smallest nonparallelism error relative to the FCI potential and the corresponding fundamental vibrational frequencies compare reasonably well with the experimental ones and are very close to those recently obtained by other authors. The effect of anharmonicity is assessed using the second-order perturbation theory (MP2). Finally, the invariance of the RMR CC methods with respect to orbital rotations is also examined.}, file = {/Users/monino/Zotero/storage/72SLN6AI/Li et Paldus - 2009 - Accounting for the exact degeneracy and quasidegen.pdf} } @article{lutz_2018, title = {Reference Dependence of the Two-Determinant Coupled-Cluster Method for Triplet and Open-Shell Singlet States of Biradical Molecules}, author = {Lutz, Jesse J. and Nooijen, Marcel and Perera, Ajith and Bartlett, Rodney J.}, year = {2018}, month = apr, journal = {J. Chem. Phys.}, volume = {148}, number = {16}, pages = {164102}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.5025170}, abstract = {We study the performance of the two-determinant (TD) coupled-cluster (CC) method which, unlike conventional ground-state single-reference (SR) CC methods, can, in principle, provide a naturally spin-adapted treatment of the lowest-lying open-shell singlet (OSS) and triplet electronic states. Various choices for the TD-CC reference orbitals are considered, including those generated by the multi-configurational self-consistent field method. Comparisons are made with the results of high-level SR-CC, equation-of-motion (EOM) CC, and multi-reference EOM calculations performed on a large test set of over 100 molecules with low-lying OSS states. It is shown that in cases where the EOMCC reference function is poorly described, TD-CC can provide a significantly better quantitative description of OSS total energies and OSS-triplet splittings.}, file = {/Users/monino/Zotero/storage/WRSTKSLY/Lutz et al. - 2018 - Reference dependence of the two-determinant couple.pdf} } @article{lyakh_2011, title = {The `Tailored' {{CCSD}}({{T}}) Description of the Automerization of Cyclobutadiene}, author = {Lyakh, Dmitry I. and Lotrich, Victor F. and Bartlett, Rodney J.}, year = {2011}, month = jan, journal = {Chemical Physics Letters}, volume = {501}, number = {4}, pages = {166--171}, issn = {0009-2614}, doi = {10.1016/j.cplett.2010.11.058}, abstract = {An alternative route to extend the CCSD(T) approach to multireference problems is presented. The well-known defect of the CCSD(T) model in describing the non-dynamic electron correlation effects is remedied by `tailoring' the underlying coupled-cluster singles and doubles (CCSD) approach and applying the perturbative triples correction to it. The TCCSD(T) approach suggested in the paper has the same computational demands as the CCSD(T) method, though being mostly free from its drawbacks pertinent to multireference (quasidegenerate) situations. To test the approach we calculate the potential energy surface for the automerization of cyclobutadiene where the transition state exhibits a strong multireference character.}, langid = {english}, file = {/Users/monino/Zotero/storage/F6XZHQI8/S0009261410015393.html} } @article{mahapatra_2010, title = {{Second-order state-specific multireference M\o ller Plesset perturbation theory: Application to energy surfaces of diimide, ethylene, butadiene, and cyclobutadiene}}, shorttitle = {{Second-order state-specific multireference M\o ller Plesset perturbation theory}}, author = {Mahapatra, Uttam Sinha and Chattopadhyay, Sudip and Chaudhuri, Rajat K.}, year = {2010}, journal = {J. Comput. Chem.}, volume = {32}, number = {2}, pages = {325--337}, issn = {1096-987X}, doi = {10.1002/jcc.21624}, abstract = {The complete active space spin-free state-specific multireference M\o ller-Plesset perturbation theory (SS-MRMPPT) based on the Rayleigh-Schr\"odinger expansion has proved to be very successful in describing electronic states of model and real molecular systems with predictive accuracy. The SS-MRMPPT method (which deals with one state while using a multiconfigurational reference wave function) is designed to avoid intruder effects along with a balanced description of both dynamic and static correlations in a size-extensive manner, which allows us to produce accurate potential energy surfaces (PESs) with a correct shape in bond-breaking processes. The SS-MRMPPT method is size consistent when localized orbitals on each fragment are used. The intruder state(s) almost inevitably interfere when computing the PESs involving the breaking of genuine chemical bonds. In such situations, the traditional effective Hamiltonian formalism often goes down, so that no physically acceptable solution can be obtained. In this work, we continue our analysis of the SS-MRMPPT method for systems and phenomena that cannot be described either with the conventional single-reference approach or effective Hamiltonian-based traditional MR methods. In this article, we investigate whether the encouraging results we have obtained at the SS-MRMPPT level in the study of cis-trans isomerization of diimide (N2H2), ethylene (C2H4), and 1,3-butadiene (C4H6) carry over to the study of chemical reactions. The energy surfaces of the double-bond flipping interconversion of the two equivalent ground and two lowest singlet state structures of cyclobutadiene have also been studied. All results have been discussed and assessed by comparing with other state-of-the-art calculations and corresponding experimental data whenever available. \textcopyright{} 2010 Wiley Periodicals, Inc. J Comput Chem, 2011}, langid = {german}, annotation = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/jcc.21624}, file = {/Users/monino/Zotero/storage/UHJ8YMNH/Mahapatra et al. - 2011 - Second-order state-specific multireference Møller .pdf;/Users/monino/Zotero/storage/JXXGY7X8/jcc.html} } @article{manohar_2008, title = {A Noniterative Perturbative Triples Correction for the Spin-Flipping and Spin-Conserving Equation-of-Motion Coupled-Cluster Methods with Single and Double Substitutions}, author = {Manohar, Prashant U. and Krylov, Anna I.}, year = {2008}, month = nov, journal = {J. Chem. Phys.}, volume = {129}, number = {19}, pages = {194105}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.3013087}, abstract = {A noniterative {$\mathsl{N}$} 7 N7 triples correction for the equation-of-motion coupled-cluster method with single and double substitutions (CCSD) is presented. The correction is derived by second-order perturbation treatment of the similarity-transformed CCSD Hamiltonian. The spin-conserving variant of the correction is identical to the triples correction of Piecuch and co-workers [Mol. Phys. 104, 2149 (2006)] derived within method-of-moments framework and is not size intensive. The spin-flip variant of the correction is size intensive. The performance of the correction is demonstrated by calculations of electronic excitation energies in methylene, nitrenium ion, cyclobutadiene, ortho-, meta-, and para-benzynes, 1,2,3-tridehydrobenzene, as well as C\textendash C bond breaking in ethane. In all cases except cyclobutadiene, the absolute values of the correction for energy differences were 0.1 eV or less. In cyclobutadiene, the absolute values of the correction were as large as 0.4 eV. In most cases, the correction reduced the errors against the benchmark values by about a factor of 2\textendash 3, the absolute errors being less than 0.04 eV.}, file = {/Users/monino/Zotero/storage/686RRDFK/Manohar et Krylov - 2008 - A noniterative perturbative triples correction for.pdf} } @book{minkin_1994, title = {Aromaticity and {{Antiaromaticity}}: {{Electronic}} and {{Structural Aspects}} | {{Wiley}}}, shorttitle = {Aromaticity and {{Antiaromaticity}}}, author = {Minkin, Vladimir I and Glukhovtsev, Mikhail N. and Simkin, Boris Ya.}, year = {1994}, file = {/Users/monino/Zotero/storage/HGW4QMJY/Aromaticity+and+Antiaromaticity+Electronic+and+Structural+Aspects-p-9780471593829.html} } @article{peverati_2011, title = {Improving the {{Accuracy}} of {{Hybrid Meta-GGA Density Functionals}} by {{Range Separation}}}, author = {Peverati, Roberto and Truhlar, Donald G.}, year = {2011}, month = nov, journal = {J. Phys. Chem. Lett.}, volume = {2}, number = {21}, pages = {2810--2817}, publisher = {{American Chemical Society}}, doi = {10.1021/jz201170d}, abstract = {The Minnesota family of exchange\textendash correlation functionals, which consists of meta generalized gradient approximations (meta-GGAs) and global-hybrid meta-GGAs, has been successful for density functional calculations of molecular structure, properties, and thermochemistry, kinetics, noncovalent interactions, and spectroscopy. Here, we generalize the functional form by using range-separated hybrid meta-GGA exchange. We optimize a functional, called M11, with the new form against a broad database of energetic chemical properties and compare its performance to that of several other functionals, including previous Minnesota functionals. We require the percentage of Hartree\textendash Fock exchange to be 100 at large interelectronic distance, and we find an optimum percentage of 42.8 at short range. M11 has good across-the-board performance and the smallest mean unsigned error over the whole test set of 332 data; it has especially good performance for main-group atomization energies, proton affinities, electron affinities, alkyl bond dissociation energies, barrier heights, noncovalent interaction energies, and charge-transfer electronic excitation.}, file = {/Users/monino/Zotero/storage/PSFGYXNN/Peverati et Truhlar - 2011 - Improving the Accuracy of Hybrid Meta-GGA Density .pdf;/Users/monino/Zotero/storage/FB9CZB9Y/jz201170d.html} } @article{qu_2015, title = {Photoisomerization of {{Silyl-Substituted Cyclobutadiene Induced}} by {$\sigma~\rightarrow$} {$\pi$}* {{Excitation}}: {{A Computational Study}}}, shorttitle = {Photoisomerization of {{Silyl-Substituted Cyclobutadiene Induced}} by {$\sigma~\rightarrow$} {$\pi$}* {{Excitation}}}, author = {Qu, Zexing and Yang, Chen and Liu, Chungen}, year = {2015}, month = jan, journal = {J. Phys. Chem. A}, volume = {119}, number = {3}, pages = {442--451}, publisher = {{American Chemical Society}}, issn = {1089-5639}, doi = {10.1021/jp503220q}, abstract = {Photoinduced chemical processes upon Franck\textendash Condon (FC) excitation in tetrakis(trimethylsilyl)-cyclobutadiene (TMS-CBD) have been investigated through the exploration of potential energy surface crossings among several low-lying excited states using the complete active space self-consistent field (CASSCF) method. Vertical excitation energies are also computed with the equation-of-motion coupled-cluster model with single and double excitations (EOM-CCSD) as well as the multireference M\o ller\textendash Plesset (MRMP) methods. Upon finding an excellent coincidence between the computational results and experimental observations, it is suggested that the Franck\textendash Condon excited state does not correspond to the first {$\pi$}\textendash{$\pi$}* single excitation state (S1, 11B1 state in terms of D2 symmetry), but to the second 1B1 state (S3), which is characterized as a {$\sigma$}\textendash{$\pi$}* single excitation state. Starting from the Franck\textendash Condon region, a series of conical intersections (CIs) are located along one isomerization channel and one dissociation channel. Through the isomerization channel, TMS-CBD is transformed to tetrakis(trimethylsilyl)-tetrahedrane (TMS-THD), and this isomerization process could take place by passing through a ``tetra form'' conical intersection. On the other hand, the dissociation channel yielding two bis(trimethylsilyl)-acetylene (TMS-Ac) molecules through further stretching of the longer C\textendash C bonds might be more competitive than the isomerization channel after excitation into S3 state. This mechanistic picture is in good agreement with recently reported experimental observations.}, file = {/Users/monino/Zotero/storage/Y3CT8YYT/Qu et al. - 2015 - Photoisomerization of Silyl-Substituted Cyclobutad.pdf;/Users/monino/Zotero/storage/W9Q4H9MA/jp503220q.html} } @article{reeves_1969, title = {Further Experiments Pertaining to the Ground State of Cyclobutadiene}, author = {Reeves, P. C. and Henery, J. and Pettit, R.}, year = {1969}, month = oct, journal = {J. Am. Chem. Soc.}, volume = {91}, number = {21}, pages = {5888--5890}, publisher = {{American Chemical Society}}, issn = {0002-7863}, doi = {10.1021/ja01049a042}, file = {/Users/monino/Zotero/storage/T44XQHXX/Reeves et al. - 1969 - Further experiments pertaining to the ground state.pdf;/Users/monino/Zotero/storage/YFJV7DYC/ja01049a042.html} } @incollection{roos_1996, title = {Multiconfigurational {{Perturbation Theory}}: {{Applications}} in {{Electronic Spectroscopy}}}, shorttitle = {Multiconfigurational {{Perturbation Theory}}}, booktitle = {Advances in {{Chemical Physics}}}, author = {Roos, Bj{\"o}rn O. and Andersson, Kerstin and F{\"u}lscher, Markus P. and Malmqvist, Per-{\^a}ke and {Serrano-Andr{\'e}s}, Luis and Pierloot, Kristin and Merch{\'a}n, Manuela}, year = {1996}, pages = {219--331}, publisher = {{John Wiley \& Sons, Ltd}}, doi = {10.1002/9780470141526.ch5}, abstract = {This chapter contains sections titled: Introduction Multiconfigurational Perturbation Theory Applications in Spectroscopy Summary}, copyright = {Copyright \textcopyright{} 1996 by John Wiley \& Sons, Inc.}, isbn = {978-0-470-14152-6}, langid = {english}, annotation = {\_eprint: https://onlinelibrary.wiley.com/doi/pdf/10.1002/9780470141526.ch5}, file = {/Users/monino/Zotero/storage/KWDFZUBF/9780470141526.html} } @article{schoonmaker_2018, title = {Quantum Mechanical Tunneling in the Automerization of Cyclobutadiene}, author = {Schoonmaker, R. and Lancaster, T. and Clark, S. J.}, year = {2018}, month = mar, journal = {J. Chem. Phys.}, volume = {148}, number = {10}, pages = {104109}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.5019254}, abstract = {Cyclobutadiene has a four-membered carbon ring with two double bonds, but this highly strained molecular configuration is almost square and, via a coordinated motion, the nuclei quantum mechanically tunnels through the high-energy square state to a configuration equivalent to the initial configuration under a 90\textdegree{} rotation. This results in a square ground state, comprising a superposition of two molecular configurations, that is driven by quantum tunneling. Using a quantum mechanical model, and an effective nuclear potential from density functional theory, we calculate the vibrational energy spectrum and the accompanying wavefunctions. We use the wavefunctions to identify the motions of the molecule and detail how different motions can enhance or suppress the tunneling rate. This is relevant for kinematics of tunneling-driven reactions, and we discuss these implications. We are also able to provide a qualitative account of how the molecule will respond to an external perturbation and how this may enhance or suppress infra-red-active vibrational transitions.}, file = {/Users/monino/Zotero/storage/EEIUEQUN/Schoonmaker et al. - 2018 - Quantum mechanical tunneling in the automerization.pdf} } @article{shao_2015, title = {Advances in Molecular Quantum Chemistry Contained in the {{Q-Chem}} 4 Program Package}, author = {Shao, Yihan and Gan, Zhengting and Epifanovsky, Evgeny and Gilbert, Andrew T.B. and Wormit, Michael and Kussmann, Joerg and Lange, Adrian W. and Behn, Andrew and Deng, Jia and Feng, Xintian and Ghosh, Debashree and Goldey, Matthew and Horn, Paul R. and Jacobson, Leif D. and Kaliman, Ilya and Khaliullin, Rustam Z. and Ku{\'s}, Tomasz and Landau, Arie and Liu, Jie and Proynov, Emil I. and Rhee, Young Min and Richard, Ryan M. and Rohrdanz, Mary A. and Steele, Ryan P. and Sundstrom, Eric J. and Woodcock, H. Lee and Zimmerman, Paul M. and Zuev, Dmitry and Albrecht, Ben and Alguire, Ethan and Austin, Brian and Beran, Gregory J. O. and Bernard, Yves A. and Berquist, Eric and Brandhorst, Kai and Bravaya, Ksenia B. and Brown, Shawn T. and Casanova, David and Chang, Chun-Min and Chen, Yunqing and Chien, Siu Hung and Closser, Kristina D. and Crittenden, Deborah L. and Diedenhofen, Michael and DiStasio, Robert A. and Do, Hainam and Dutoi, Anthony D. and Edgar, Richard G. and Fatehi, Shervin and {Fusti-Molnar}, Laszlo and Ghysels, An and {Golubeva-Zadorozhnaya}, Anna and Gomes, Joseph and {Hanson-Heine}, Magnus W.D. and Harbach, Philipp H.P. and Hauser, Andreas W. and Hohenstein, Edward G. and Holden, Zachary C. and Jagau, Thomas-C. and Ji, Hyunjun and Kaduk, Benjamin and Khistyaev, Kirill and Kim, Jaehoon and Kim, Jihan and King, Rollin A. and Klunzinger, Phil and Kosenkov, Dmytro and Kowalczyk, Tim and Krauter, Caroline M. and Lao, Ka Un and Laurent, Ad{\`e}le D. and Lawler, Keith V. and Levchenko, Sergey V. and Lin, Ching Yeh and Liu, Fenglai and Livshits, Ester and Lochan, Rohini C. and Luenser, Arne and Manohar, Prashant and Manzer, Samuel F. and Mao, Shan-Ping and Mardirossian, Narbe and Marenich, Aleksandr V. and Maurer, Simon A. and Mayhall, Nicholas J. and Neuscamman, Eric and Oana, C. Melania and {Olivares-Amaya}, Roberto and O'Neill, Darragh P. and Parkhill, John A. and Perrine, Trilisa M. and Peverati, Roberto and Prociuk, Alexander and Rehn, Dirk R. and Rosta, Edina and Russ, Nicholas J. and Sharada, Shaama M. and Sharma, Sandeep and Small, David W. and Sodt, Alexander and Stein, Tamar and St{\"u}ck, David and Su, Yu-Chuan and Thom, Alex J.W. and Tsuchimochi, Takashi and Vanovschi, Vitalii and Vogt, Leslie and Vydrov, Oleg and Wang, Tao and Watson, Mark A. and Wenzel, Jan and White, Alec and Williams, Christopher F. and Yang, Jun and Yeganeh, Sina and Yost, Shane R. and You, Zhi-Qiang and Zhang, Igor Ying and Zhang, Xing and Zhao, Yan and Brooks, Bernard R. and Chan, Garnet K.L. and Chipman, Daniel M. and Cramer, Christopher J. and Goddard, William A. and Gordon, Mark S. and Hehre, Warren J. and Klamt, Andreas and Schaefer, Henry F. and Schmidt, Michael W. and Sherrill, C. David and Truhlar, Donald G. and Warshel, Arieh and Xu, Xin and {Aspuru-Guzik}, Al{\'a}n and Baer, Roi and Bell, Alexis T. and Besley, Nicholas A. and Chai, Jeng-Da and Dreuw, Andreas and Dunietz, Barry D. and Furlani, Thomas R. and Gwaltney, Steven R. and Hsu, Chao-Ping and Jung, Yousung and Kong, Jing and Lambrecht, Daniel S. and Liang, WanZhen and Ochsenfeld, Christian and Rassolov, Vitaly A. and Slipchenko, Lyudmila V. and Subotnik, Joseph E. and Van Voorhis, Troy and Herbert, John M. and Krylov, Anna I. and Gill, Peter M.W. and {Head-Gordon}, Martin}, year = {2015}, month = jan, journal = {Mol. Phys.}, volume = {113}, number = {2}, pages = {184--215}, publisher = {{Taylor \& Francis}}, issn = {0026-8976}, doi = {10.1080/00268976.2014.952696}, abstract = {A summary of the technical advances that are incorporated in the fourth major release of the Q-Chem quantum chemistry program is provided, covering approximately the last seven years. These include developments in density functional theory methods and algorithms, nuclear magnetic resonance (NMR) property evaluation, coupled cluster and perturbation theories, methods for electronically excited and open-shell species, tools for treating extended environments, algorithms for walking on potential surfaces, analysis tools, energy and electron transfer modelling, parallel computing capabilities, and graphical user interfaces. In addition, a selection of example case studies that illustrate these capabilities is given. These include extensive benchmarks of the comparative accuracy of modern density functionals for bonded and non-bonded interactions, tests of attenuated second order M\o ller\textendash Plesset (MP2) methods for intermolecular interactions, a variety of parallel performance benchmarks, and tests of the accuracy of implicit solvation models. Some specific chemical examples include calculations on the strongly correlated Cr2 dimer, exploring zeolite-catalysed ethane dehydrogenation, energy decomposition analysis of a charged ter-molecular complex arising from glycerol photoionisation, and natural transition orbitals for a Frenkel exciton state in a nine-unit model of a self-assembling nanotube.}, annotation = {\_eprint: https://doi.org/10.1080/00268976.2014.952696}, file = {/Users/monino/Zotero/storage/WKMD4DBC/Shao et al. - 2015 - Advances in molecular quantum chemistry contained .pdf;/Users/monino/Zotero/storage/TBGBBMR4/00268976.2014.html} } @article{shen_2012, title = {Combining Active-Space Coupled-Cluster Methods with Moment Energy Corrections via the {{CC}}({{P}};{{Q}}) Methodology, with Benchmark Calculations for Biradical Transition States}, author = {Shen, Jun and Piecuch, Piotr}, year = {2012}, month = apr, journal = {J. Chem. Phys.}, volume = {136}, number = {14}, pages = {144104}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.3700802}, abstract = {We have recently suggested the CC(P;Q) methodology that can correct energies obtained in the active-space coupled-cluster (CC) or equation-of-motion (EOM) CC calculations, which recover much of the nondynamical and some dynamical electron correlation effects, for the higher-order, mostly dynamical, correlations missing in the active-space CC/EOMCC considerations. It is shown that one can greatly improve the description of biradical transition states, both in terms of the resulting energy barriers and total energies, by combining the CC approach with singles, doubles, and active-space triples, termed CCSDt, with the CC(P;Q)-style correction due to missing triple excitations defining the CC(t;3) approximation.}, file = {/Users/monino/Zotero/storage/C6324F9Y/Shen et Piecuch - 2012 - Combining active-space coupled-cluster methods wit.pdf} } @article{stoneburner_2017, title = {Systematic Design of Active Spaces for Multi-Reference Calculations of Singlet\textendash Triplet Gaps of Organic Diradicals, with Benchmarks against Doubly Electron-Attached Coupled-Cluster Data}, author = {Stoneburner, Samuel J. and Shen, Jun and Ajala, Adeayo O. and Piecuch, Piotr and Truhlar, Donald G. and Gagliardi, Laura}, year = {2017}, month = oct, journal = {J. Chem. Phys.}, volume = {147}, number = {16}, pages = {164120}, publisher = {{American Institute of Physics}}, issn = {0021-9606}, doi = {10.1063/1.4998256}, abstract = {Singlet-triplet gaps in diradical organic {$\pi$}-systems are of interest in many applications. In this study, we calculate them in a series of molecules, including cyclobutadiene and its derivatives and cyclopentadienyl cation, by using correlated participating orbitals within the complete active space (CAS) and restricted active space (RAS) self-consistent field frameworks, followed by second-order perturbation theory (CASPT2 and RASPT2). These calculations are evaluated by comparison with the results of doubly electron-attached (DEA) equation-of-motion (EOM) coupled-cluster (CC) calculations with up to 4-particle\textendash 2-hole (4p-2h) excitations. We find active spaces that can accurately reproduce the DEA-EOMCC(4p-2h) data while being small enough to be applicable to larger organic diradicals.}, file = {/Users/monino/Zotero/storage/WXJDP8H3/Stoneburner et al. - 2017 - Systematic design of active spaces for multi-refer.pdf} } @article{varras_2018, title = {The Transition State of the Automerization Reaction of Cyclobutadiene: {{A}} Theoretical Approach Using the {{Restricted Active Space Self Consistent Field}} Method}, shorttitle = {The Transition State of the Automerization Reaction of Cyclobutadiene}, author = {Varras, Panayiotis C. and Gritzapis, Panagiotis S.}, year = {2018}, month = nov, journal = {Chemical Physics Letters}, volume = {711}, pages = {166--172}, issn = {0009-2614}, doi = {10.1016/j.cplett.2018.09.028}, abstract = {The application of the Restricted Active Space Self Consistent Field (RASSCF) quantum chemical method using an extended active space and including {$\sigma$}-{$\sigma$}, {$\pi$}-{$\sigma$} and {$\pi$}-{$\pi$} dynamical electron correlation shows that the transition state structure for the automerization reaction of cyclobutadiene is an isosceles trapezium. This transition state is obtained without any symmetry constraints. The calculated energy barrier height involving the zero point vibrational energy corrections is 9.62\,kcal{$\bullet$}mol-1 (0.417\,eV), with the corresponding rate constant being equal to 0.18\,\texttimes\,109\,s-1 (or 7.1\,\texttimes\,1010\,s-1 in case of using the vibrational energy splitting tunneling method).}, langid = {english}, file = {/Users/monino/Zotero/storage/X7QFY28N/S0009261418307590.html} } @article{vitale_2020, title = {{{FCIQMC-Tailored Distinguishable Cluster Approach}}}, author = {Vitale, Eugenio and Alavi, Ali and Kats, Daniel}, year = {2020}, month = sep, journal = {J. Chem. Theory Comput.}, volume = {16}, number = {9}, pages = {5621--5634}, publisher = {{American Chemical Society}}, issn = {1549-9618}, doi = {10.1021/acs.jctc.0c00470}, abstract = {The tailored approach is applied to the distinguishable cluster method together with a stochastic FCI solver (FCIQMC). It is demonstrated that the new method is more accurate than the corresponding tailored coupled cluster and the pure distinguishable cluster methods. An F12 correction for tailored methods and FCIQMC is introduced, which drastically improves the basis set convergence. A new black-box approach to define the active space using the natural orbitals from the distinguishable cluster is evaluated and found to be a convenient alternative to the usual CASSCF approach.}, file = {/Users/monino/Zotero/storage/IWWZ436M/Vitale et al. - 2020 - FCIQMC-Tailored Distinguishable Cluster Approach.pdf;/Users/monino/Zotero/storage/XFRQ8TP9/acs.jctc.html} } @article{whitman_1982, title = {Limits on the Activation Parameters for Automerization of Cyclobutadiene-1,2-D2}, author = {Whitman, David W. and Carpenter, Barry K.}, year = {1982}, month = nov, journal = {J. Am. Chem. Soc.}, volume = {104}, number = {23}, pages = {6473--6474}, publisher = {{American Chemical Society}}, issn = {0002-7863}, doi = {10.1021/ja00387a065}, file = {/Users/monino/Zotero/storage/9AK8SNDG/Whitman et Carpenter - 1982 - Limits on the activation parameters for automeriza.pdf;/Users/monino/Zotero/storage/WRSENMYS/ja00387a065.html} } @article{xu_2015, title = {Multireference {{Second Order Perturbation Theory}} with a {{Simplified Treatment}} of {{Dynamical Correlation}}}, author = {Xu, Enhua and Zhao, Dongbo and Li, Shuhua}, year = {2015}, month = oct, journal = {J. Chem. Theory Comput.}, volume = {11}, number = {10}, pages = {4634--4643}, publisher = {{American Chemical Society}}, issn = {1549-9618}, doi = {10.1021/acs.jctc.5b00495}, abstract = {A multireference second order perturbation theory based on a complete active space configuration interaction (CASCI) function or density matrix renormalized group (DMRG) function has been proposed. This method may be considered as an approximation to the CAS/A approach with the same reference, in which the dynamical correlation is simplified with blocked correlated second order perturbation theory based on the generalized valence bond (GVB) reference (GVB-BCPT2). This method, denoted as CASCI-BCPT2/GVB or DMRG-BCPT2/GVB, is size consistent and has a similar computational cost as the conventional second order perturbation theory (MP2). We have applied it to investigate a number of problems of chemical interest. These problems include bond-breaking potential energy surfaces in four molecules, the spectroscopic constants of six diatomic molecules, the reaction barrier for the automerization of cyclobutadiene, and the energy difference between the monocyclic and bicyclic forms of 2,6-pyridyne. Our test applications demonstrate that CASCI-BCPT2/GVB can provide comparable results with CASPT2 (second order perturbation theory based on the complete active space self-consistent-field wave function) for systems under study. Furthermore, the DMRG-BCPT2/GVB method is applicable to treat strongly correlated systems with large active spaces, which are beyond the capability of CASPT2.}, file = {/Users/monino/Zotero/storage/NMUPRMKE/Xu et al. - 2015 - Multireference Second Order Perturbation Theory wi.pdf;/Users/monino/Zotero/storage/A5RR8VJ5/acs.jctc.html} } @article{yanai_2004a, title = {A New Hybrid Exchange\textendash Correlation Functional Using the {{Coulomb-attenuating}} Method ({{CAM-B3LYP}})}, author = {Yanai, Takeshi and Tew, David P and Handy, Nicholas C}, year = {2004}, month = jul, journal = {Chemical Physics Letters}, volume = {393}, number = {1}, pages = {51--57}, issn = {0009-2614}, doi = {10.1016/j.cplett.2004.06.011}, abstract = {A new hybrid exchange\textendash correlation functional named CAM-B3LYP is proposed. It combines the hybrid qualities of B3LYP and the long-range correction presented by Tawada et al. [J. Chem. Phys., in press]. We demonstrate that CAM-B3LYP yields atomization energies of similar quality to those from B3LYP, while also performing well for charge transfer excitations in a dipeptide model, which B3LYP underestimates enormously. The CAM-B3LYP functional comprises of 0.19 Hartree\textendash Fock (HF) plus 0.81 Becke 1988 (B88) exchange interaction at short-range, and 0.65 HF plus 0.35 B88 at long-range. The intermediate region is smoothly described through the standard error function with parameter 0.33.}, langid = {english}, file = {/Users/monino/Zotero/storage/85SV7MII/Yanai et al. - 2004 - A new hybrid exchange–correlation functional using.pdf;/Users/monino/Zotero/storage/N5PL4H9N/S0009261404008620.html} } @article{zhao_2008, title = {The {{M06}} Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements: Two New Functionals and Systematic Testing of Four {{M06-class}} Functionals and 12 Other Functionals}, shorttitle = {The {{M06}} Suite of Density Functionals for Main Group Thermochemistry, Thermochemical Kinetics, Noncovalent Interactions, Excited States, and Transition Elements}, author = {Zhao, Yan and Truhlar, Donald G.}, year = {2008}, month = may, journal = {Theor Chem Account}, volume = {120}, number = {1}, pages = {215--241}, issn = {1432-2234}, doi = {10.1007/s00214-007-0310-x}, abstract = {We present two new hybrid meta exchange- correlation functionals, called M06 and M06-2X. The M06 functional is parametrized including both transition metals and nonmetals, whereas the M06-2X functional is a high-nonlocality functional with double the amount of nonlocal exchange (2X), and it is parametrized only for nonmetals.The functionals, along with the previously published M06-L local functional and the M06-HF full-Hartree\textendash Fock functionals, constitute the M06 suite of complementary functionals. We assess these four functionals by comparing their performance to that of 12 other functionals and Hartree\textendash Fock theory for 403 energetic data in 29 diverse databases, including ten databases for thermochemistry, four databases for kinetics, eight databases for noncovalent interactions, three databases for transition metal bonding, one database for metal atom excitation energies, and three databases for molecular excitation energies. We also illustrate the performance of these 17 methods for three databases containing 40 bond lengths and for databases containing 38 vibrational frequencies and 15 vibrational zero point energies. We recommend the M06-2X functional for applications involving main-group thermochemistry, kinetics, noncovalent interactions, and electronic excitation energies to valence and Rydberg states. We recommend the M06 functional for application in organometallic and inorganometallic chemistry and for noncovalent interactions.}, langid = {english}, file = {/Users/monino/Zotero/storage/9VH8QARI/Zhao et Truhlar - 2008 - The M06 suite of density functionals for main grou.pdf} }