Locating the lowest free-energy point on conical intersection in polar solvent:Reference interaction site model self-consistent field study of ethylene and CH_2NH_2~+

摘要

We present a theoretical method for locating the lowest free-energy points on conical intersections (CIs) in solution using the reference interaction site model self-consistent field (RISM-SCF) theory.Based on the linear-response theory,the nonequilibrium free energy is defined as a quadratic function of solvation coordinates,the parameters in which are directly obtained by ab initio RISM-SCF calculations.This free energy is easily incorporated into an efficient CI optimization procedure in gas phase.The present method is applied to the cis-trans photoisomerizations of ethylene and methaniminium cation (CH_2NH_2~+) in polar solvents.We show that the geometries and energies of CIs are largely affected by the solute-solvent electrostatic interaction.In particular,the hydrogen migration of ethylene observed at CIs in the gas phase disappears in protic solvents due to the large stabilization of the zwitterionic state.