Du contenu simple
Du contenu complexe, avec un [lien->https://google.com] dedans
Du contenu simple mais dans un paragraphe justifié
Du contenu simple mais dans un paragraphe justifié avec des guillemets
{{{Un paragraphe justifié}}}Anthony Scemama, l'un des deux coordinateurs du CNRS pour le centre d'excellence européen H2020 [T.REX->https://trex-coe.eu/], répond aux questions de "CNRS Le Journal" sur la révolution exascale des supercalculateurs.
[Lien vers l'article->https://lejournal.cnrs.fr/articles/revolution-en-vue-pour-percer-les-secrets-de-la-matiere] from {{ A. Simon, C. Iftner, J. Mascetti, F. Spiegelman ’Water clusters in an argon matrix : infrared spectra from molecular dynamics simulations with a self-consistent charge density functional based tight binding/force field potential’ J. Phys. Chem. A 2015, 119, 2449-2467 (DOI : 10.1021/jp508533k)}} ABSTRACT: The present theoretical study aims at investigating the effects of an argon matrix on the structures, energetics, dynamics, and infrared (IR) spectra of small water clusters (H2O)n (n = 1−6). The potential energy surface is obtained from a hybrid selfconsistent charge density functional-based tight binding/force-field approach (SCCDFTB/FF) in which the water clusters are treated at the SCC-DFTB level and the matrix is modeled at the FF level by a cluster consisting of ∼340 Ar atoms with a face centered cubic (fcc) structure, namely (H2O)n/Ar. With respect to a pure FF scheme, this allows a quantum description of the molecular system embedded in the matrix, along with all-atom geometry optimization and molecular dynamics (MD) simulations of the (H2O)n/Ar system. Finite-temperature IR spectra are derived from the MD simulations. The SCC-DFTB/FF scheme is first benchmarked on (H2O)Arn clusters against correlated wave function results and DFT calculations performed in the present work, and against FF data available in the literature. Regarding (H2O)n/Ar systems, the geometries of the water clusters are found to adapt to the fcc environment, possibly leading to intermolecular distortion and matrix perturbation. Several energetical quantities are estimated to characterize the water clusters in the matrix. In the particular case of the water hexamer, substitution and insertion energies for the prism, bag, and cage are found to be lower than that for the 6-member ring isomer. Finite-temperature MD simulations show that the water monomer has a quasifree rotation motion at 13 K, in agreement with experimental data. In the case of the water dimer, the only large-amplitude motion is a distortion−rotation intermolecular motion, whereas only vibration motions around the nuclei equilibrium positions are observed for clusters with larger sizes. Regarding the IR spectra, we find that the matrix environment leads to redshifts of the stretching modes and almost no shift of the bending modes. This is in agreement with experimental data. Furthermore, in the case of the water monomer and dimer, the magnitudes of the computed shifts are in fair agreement with the experimental values. The complex case of the water hexamer, which presents several low-energy isomers, is discussed. * {{Electronic Spectra of [FePAH]+ complexes in the Region of the Diffuse Interstellar Bands by means of multireference wavefunction calculations. }} This is done in collaboration with Nadia Ben Amor (GMO group). from {{ M. Lanza, A. Simon, N. Ben Amor ’Electronic Spectroscopy of [FePAH]+ complexes in the Region of the Diffuse Interstellar Bands : Multireference Wavefunction Studies on [FeC6H6]+’ J. Phys. Chem. A 2015, 119, 6123-6130 (DOI : 10.1021/acs.jpca.5b00438)}} ABSTRACT: The low-energy states and electronic spectrum in the nearinfrared− visible region of [FeC6H6]+ are studied by theoretical approaches. An exhaustive exploration of the potential energy surface of [FeC6H6]+ is performed using the density functional theory method. The ground state is found to be a 4A1 state. The structures of the lowest energy states (4A2 and 4A1) are used to perform multireference wave function calculations by means of the multistate complete active space with perturbation at the second order method. Contrary to the density functional theory results (4A1 ground state), multireference perturbative calculations show that the 4A2 state is the ground state. The vertical electronic spectrum is computed and compared with the astronomical diffuse interstellar bands, a set of near-infrared-visible bands detected on the extinction curve in our and other galaxies. Many transitions are found in this domain, corresponding to d → d, d → 4s, or d → π* excitations, but few are allowed and, if they are, their oscillation strengths are small. Even though some band positions could match some of the observed bands, the relative intensities do not fit, making the contribution of the [Fe−C6H6]+ complexes to the diffuse interstellar bands questionable. This work, however, lays the foundation for the studies of polycyclic aromatic hydrocarbons (PAHs) complexed to Fe cations that are more likely to possess d → π* and π → π* transitions in the diffuse interstellar bands domain. PAH ligands indeed possess a larger number of π and π* orbitals, respectively, higher and lower in energy than those of C6H6, which are expected to lead to lower energy d → π* and π → π* transitions in [FePAH]+ than in [FeC6H6]+ complexes.