Perturbation theory of the electron correlation effects for atomic and molecular properties. III. Fourth-order corrections to molecular dipole moments and polarizabilities

Abstract

The correlation corrections to molecular electric properties are studied through the fourth-order with respect to the correlation perturbation. The limitation of the corresponding perturbation theory to contributions due to singly and doubly excited states is accompanied by a simultaneous neglect of the pertinent renormalization term. The validity of the resulting approximate fourth-order theory is illustrated by computing the correlation corrections to dipole moments and polarizabilities of FH, H 2O, NH 3, and CH 4. Our results are compared with the appropriate CEPA values calculated with virtually the same basis set. It is concluded that the present fourth-order treatment accounts for the major portion of the electron correlation contribution to both dipole moments and polarizabilities of small molecules.