Medium effects on the molecular electronic structure. I. The formulation of a theory for the estimation of a molecular electronic structure surrounded by an anisotropic medium

A theory has been developed for estimation of the electronic structure of molecules embedded in an anisotropic (inhomogeneous) medium. It is assumed that the medium surrounding a solute molecule is composed of more than two polarizable dielectrics with different dielectric constants and that the dielectrics contact each other through arbitrary shaped boundaries. Then, the charge distribution in the solute molecule interacts with the dielectrics through a reaction field. The boundary element method is introduced to obtain a numerical solution to the Poisson equation with necessary boundary conditions. The expressions for the total energy of the molecule and the Helmholtz free energy of the system are given under the Hartree–Fock–Roothaan approximation. The Fock matrix is derived by taking into account nonlinearity of the Schrödinger equation in wave function. The present theory is generally applicable to the problem of medium effects when the medium surrounding a molecule is inhomogeneous and could be approximated by a multidielectric system.