Finite-field many-body perturbation theory

The results of complete fourth order many-body perturbation theory (MBPT) calculations of the quadrupole moment tensor for the FH and H2O molecules are presented. The finite-field method employed in this study is based on the coupled Hartree-Fock (CHF) solutions for the externally perturbed system. The results are very close to the available experimental data. Of interesting features of the correlation perturbation series for the quadrupole moment components one should mention that the fourth order correlation correction is dominated by contributions involving triple and single substitutions in the reference Hartree-Fock function. Moreover, the correlation perturbation series for quadrupole moments appears to be less regular than the corresponding series for molecular dipole moments. Additionally complete fourth order MBPT calculations are performed for the quadrupole polarizability tensor of FH and H2O. The correlation corrections to the corresponding CHF values are large and exhibit similar regularities as in the case of molecular dipole polarizabilities.