Solvent Effects on Electronically Excited States Using the Conductor-Like Screening Model and the Second-Order Correlated Method ADC(2)

The conductor-like screening model (COSMO) is used to treat solvent effects on excited states within a correlated method based on the algebraic-diagrammatic construction through second-order ADC(2). The origin of solvent effects is revisited, and it is pointed out that two types of contributions have to be considered. One effect is due to the change of the solute's charge distribution after excitation, which triggers a reorganization of the solvent. Initially, only the electronic degrees of freedom adapt to the new charge distribution (nonequilibrium case); for sufficiently long-lived states, the reorientation of the solvent molecules contributes, as well (equilibrium case). The second effect is the coupling of the transition densities to the fast (purely electronic) response of the solvent molecules, which can be viewed as excitonic coupling between solute and solvent molecules. This interaction is also responsible for the screening of excitonic couplings between spatially separated chromophores. While most previous implementations of comparable continuum solvation models only include either of both effects, we argue that both contributions should be taken into account. Both effects can significantly influence the excitation energy and excited state properties of the solute, as exemplified for the pi-pi* and n-pi* excitations of acrolein, and no a priori reason exists to neglect either. The implementation is also tested for the excitonic coupling of the ethene dimer where linear response contributions are indispensable for recovering the screening effects due to the solvent. Example applications to larger cases are provided, too. We discuss the excitonic coupling in a linked dyad consisting of two perylene-tetracarboxy- diimide chromophores, and the solvent effects on an intramolecular charge- transfer state of 4-(N,N-dimethylamino)benzonitrile.