EFFECT OF ELECTRON CORRELATION ON THE ELECTRON-DENSITY DISTRIBUTION AND (HYPER)POLARIZABILITY OF MOLECULES

The influence of electron correlation, calculated with Moller-Plesset perturbation theory, on the electron density distribution and (hyper)polarizability of molecules is discussed. Although the electron correlation contribution to the density is small compared with the total molecular density, it yields significant changes in atomic charges, compared to Hartree-Fock calculated values. In molecules with C=O bonds, atomic charges of the electron correlation density show a larger transferability between molecules than atomic charges calculated with the Hartree-Fock method. Two finite field methods and the sum over states method have been used to calculate the influence of an electric field of the molecules. The influence of electron correlation on the polarizability is small but can be quite large for the first hyperpolarizability, as seen, for example, in planar p-nitroaniline.