Excited states and solvatochromic shifts within a nonequilibrium solvation approach: A new formulation of the integral equation formalism method at the self-consistent field, configuration interaction, and multiconfiguration self-consistent field level

The effects of the solvation on excited states are studied in the framework of a nonequilibrium regime between solute and solvent charge distributions. The approach, which exploits a separation of the polarization into slow and fast components, is inserted in a new formulation of the recently developed continuum solvation model known as integral equation formalism. This new version, implying a large computational gain both in time consuming and memory occupation, is here implemented at the Hartree–Fock level as well as at the multiconfiguration self-consistent field and configuration interaction levels. Examples of application of the method to solvatochromic shifts for low-lying excitation energies of formaldehyde, acetaldehyde, and acetone in water are shown.