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For a given electronic excited state, the 0-0 energy ($T_0$ or $T_{00}$) is the simplest property allowing straightforward and physically-sound comparisons between theory and (accurate) experiment. However, the computation of 0-0 energies with \emph{ab initio} approaches requires determining both the structure and the vibrational frequencies of the excited state, which limits the quality of the theoretical models that can be considered in practice. This explains why only a rather limited, yet constantly increasing, number of works have been devoted to the determination of this property. In this contribution, we review these efforts with a focus on benchmark studies carried out for both gas phase and solvated compounds. Over the years, not only as the size of the molecules increased, but the refinement of the theoretical tools has followed the same trend. Though the results obtained in these benchmarks significantly depend on both the details of the protocol and the nature of the excited states, one can now roughly estimate, in the case of valence transitions, the overall accuracy of theoretical schemes as follows: $1$ eV for CIS, $0.2$--$0.3$ eV for CIS(D), $0.2$--$0.4$ eV for TD-DFT when one employs hybrid functionals, $0.1$--$0.2$ eV for ADC(2) and CC2, and $0.04$ eV for CC3, the latter approach being the only one delivering chemical accuracy on a near-systematic basis., Comment: 15 pages, 6 figures

P.F.L. thanks the Australian Research Council for a Discovery Early Career Researcher Award (Grant No. DE130101441) and a Discovery Project grant (DP140104071). P.M.W.G. thanks the Australian Research Council for funding (Grants No. DP120104740 and DP140104071).

We show that, in the high-density limit, restricted Moller-Plesset (RMP) perturbation theory yields E (2) RMP = π

International audience; The gas-phase electron attachment of thiaselena and diselena derivatives is investigated on model organic systems by ab initio calculations (level of theory MP2/DZP++). Electronic contributions favor the one-electron addition on selenium-containing compounds, with adiabatic electron affinities of 0.03, 0.24, and 0.43 eV, respectively, for dimethyldisulfide, dimethylselenenylsulfide, and dimethyldiselenide. This ensures the possibility of an excess electron binding on [BOND]Se[BOND]S[BOND] and [BOND]Se[BOND]Se[BOND] linkages. The so-formed radical anionic intermediates present a three-electrons two-centers 2c[BOND]3e bond, whose nature is confirmed by Mulliken spin densities and NBO analysis. They are stable towards dissociation, with a low barrier evaluated between about 25–60 kJ/mol. Cyclization strongly enhances dichalcogen propensity to fix an excess electron. Adiabatic electron affinities of a series of 1,2-thiaselena-cycloalkanes and 1,2-diselena-cycloalkanes are positive and range from 0.24 to 1.30 eV. This can be traced back to the release of ring strain energy upon one-electron addition: this geometrical effect is nevertheless less marked than for disulfide analogs. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

We report the calculation of core-ionized states of small organic compounds and macromolecular systems in the framework of a new method based on the local self-consistent field (LSCF). This new theoretical scheme avoids the variational collapse of the empty core orbital (CO) of the core-excited states and ensures the orthogonality between the ground state and the excited states. Compared to experimental data and other theoretical methods, accurate carbon 1s ionization energies using the Boys-Foster (BF) localization criterion for the determination of the CO and the PBE0/6-311G**//B3LYP/ 6-311G** level of theory was obtained to calculate both the ground and excited states. The macromolecular systems, a sequence of 15 alanine amino acids in both -helix and - sheet conformations, are computed using hybrid quantum mechanics/molecular mechanics (QM/MM) method within the LSCF/MM framework. The results show a weak impact of the MM surrounding in the alanine polypeptides cases compared with that of previous studies based on electrically charged residue, such as glutamate in the crambin protein.

We report the calculation of liquid-phase infrared (IR) and ultraviolet (UV) spectra in the framework of the solute's response to the reaction field of several solvents. In particular, we compare these two properties for the multipolar expansion model developed in the Nancy continuum model (NCM) and the polarized continuum model (PCM) scheme developed in Pise and Naples. All calculations are carried out at the (TD-)DFT/6-311G(2d,2p) level of theory. The cavity size used for modeling the solute effects on the IR and UV spectra are examined. To calibrate the solute cavity size, we have investigated the IR spectra of coumarin and of a set of 14 additional solutes of different size and polarity in several dielectrical surroundings. It turns out that: (i) PCM and NCM present an identical behavior when a common cavity is used to calibrate the models; and (ii) for both NCM and PCM models, the IR spectra are highly sensitive to the solute and solvent polarity. The UV/VIS investigation of coumarin derivatives