Perturbation theory of the electron correlation effects for atomic and molecular properties. VII. Complete fourth-order MBPT study of the dipole moment and dipole polarizability of H2O

Abstract

The dipole moment and dipole polarizability tensor of the water molecule are calculated by using a complete fourth-order many-body perturbation theory (MBPT) approach based on the coupled Hartree-Fock (CHF) solution for the one-electron perturbation problem. The CHF-based MBPT calculations reveal that the fourth-order correlation corrections involving triple and single substitutions in the reference HF determinant are by no means negligible. On the contrary they represent the two largest in magnitude fourth-order terms. The present study reveals that good results obtained with several approximate fourth-order MBPT schemes follow from some mutual cancellations between the neglected lower and higher-order contributions. Among these approximate MBPT approaches particular attention is given to the CHF-based MBPT treatment which involves only singly and doubly substituted states (SD-MBPT) and which provides a reasonable agreement with both the experimental data and more accurate theoretical values.