Photoelectron spectroscopy is a powerful approach to determine the electron binding energies in molecular species and materials. These, together with electron affinities, are essential quantities for understanding reactivity in gas phase and in solution, as well as the structure of the solvent around a solute [1]. In this contribution we discuss how one can employ WFT-in-DFT embedding to obtain the photoelectron spectra in the valence region for solvated species, in such a way that information on both the solvent and solute binding energies can be obtained at a reasonable computational cost while accounting for specific interactions such as hydrogen bonding. We apply our approach to the determination of the photoelectron spectra in the valence region of halide ions (X−, X = F-At) in aqueous solution, which show a rather large solvent effect that can not be captured with implicit models [2]. We model our systems as water droplets with 50 water molecules and the halogen ions [3], with structures taken from classical molecular dynamics (CMD) simulations with polarizable force fields, which reproduce the radial distributions obtained from periodic calculations [4]. Due to the increasing importance of relativistic effects [5] along the series, the binding energies for the solute are obtained with two-component molecular mean-field EOM-IP-CCSD calcu- lations, while those of the solvent are obtained with scalar ZORA calculations with the SAOP model potential. We show our fully quantum mechanical treatment of the electronic structure for the droplet does indeed yield accurate results while considering only the halide as the solute, with the exception of F−, whose valence p orbitals strongly mix with those of the closest water molecules. It was nevertheless important to relax (in the FDE treatment) the densities of the water molecules in both first and second solvation shells, due to the long-range influence of the charged halide species.

Predicting photoelectron spectra solvated species with WFT-in-DFT embedding

2019 Spring National Meeting

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