42 lines
2.4 KiB
TeX
42 lines
2.4 KiB
TeX
\documentclass[10pt]{letter}
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\usepackage{UPS_letterhead,xcolor,mhchem,ragged2e}
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\newcommand{\alert}[1]{\textcolor{red}{#1}}
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\definecolor{darkgreen}{HTML}{009900}
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\begin{document}
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\begin{letter}%
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{To the Editors of the Journal of Physical Chemistry A,}
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\opening{Dear Editors,}
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\justifying
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Please find enclosed our manuscript entitled \textit{``Reference Energies for Cyclobutadiene: Automerization and Excited States''}, which we would like you to consider as a Regular Article in the \textit{Journal of Physical Chemistry A}.
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This contribution has never been submitted in total nor in parts to any other journal, and has been seen and approved by all authors.
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The cyclobutadiene molecule has been a real challenge for both experimental and theoretical chemistry for many decades.
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In particular, cyclobutadiene is a well-known playground for theoretical chemists and is particularly suitable to test ground- and excited-state methods.
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In the $D_{2h}$ symmetry, the ground state has a weak multi-configurational character with well-separated frontier orbitals that can be described by single-reference methods.
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However, in the $D_{4h}$ symmetry, the ground state is a diradical that has two degenerate singly occupied frontier orbitals.
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In the present paper, we assess a larger number of computational methods on the automerization barrier and the vertical excitation energies of cyclobutadiene in its square ($D_{4h}$) and rectangular ($D_{2h}$) geometries, for which we have defined theoretical best estimates based on high-level coupled-cluster calculations.
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In particular, selected configuration interaction, multi-reference perturbation theory (CASSCF, CASPT2, and NEVPT2), and coupled-cluster calculations are performed.
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These wave function methods are compared with the cheaper spin-flip formalism which is tested within TD-DFT and the ADC scheme.
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Several important take-home messages are extracted from the present study, such as the excellent performance of hybrid functionals with a large amount of exact exchange, the outstanding accuracy of the ADC schemes, the importance of the $\sigma$-$\pi$ coupling in multi-configurational calculations, and the importance of quadruple excitations to reach high accuracy in coupled-cluster theory.
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We suggest David Casanova, Miquel Huix-Rotllant, Michael Filatov, Donald Truhlar, and Andreas Dreuw as potential referees.
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We look forward to hearing from you.
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\closing{Sincerely, the authors.}
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\end{letter}
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\end{document}
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