Self-consistent reaction field calculations of photoelectron binding energies for solvated molecules

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Abstract
The multiconfigurational self-consistent reaction field (MCSCRF) and the self-consistent reaction field (SCRF) methods are applied for solvation shifts of molecular photoelectron spectra. Calculations are performed for cavity wave functions of water, benzene, methanol, and formamide surrounded by dielectric continua corresponding to various solvents. The cavity wave functions for single- or multiconfigurational closed- and open-shell states are optimized self-consistently with their reaction fields, using either a continuum approach with one solute molecule embedded in the dielectric medium or a semicontinuum approach with one solute molecule and a solvation shell of molecules surrounded by the dielectric medium. The application of the MCSCRF/SCRF model gives new insight into the effects of a solvent on ionization spectra. The origin of both absolute and differential shifts upon solvation is investigated. This includes studies of local vs delocalized ionization, role of dielectric polarization vs reaction field contributions to the solvation shift, optical vs static dielectric response of the medium, and use of noncorrelated vs correlated solute wave functions. It is found that the use of the semicontinuum model with one solvation shell is often crucial to obtain experimental agreement. Comparatively large multipolar expansions of the solute charge distribution is often needed to adequately treat the solvent interaction. The results for differential core–valence and core–core shifts lead to some interesting observations that can be further explored using photoelectron and soft x-ray spectroscopic techniques.

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