Mutual dependence of relativistic and electron correlation contributions to molecular properties: the dipole moment of AgH

Abstract

A method for the evaluation of relativistic contributions to atomic and molecular properties is presented. The proposed method is based on the Cowan—Griffin quasi-relativistic approximation for a many-electron Hamiltonian. The respective relativistic corrections to properties of many-electron systems are evaluated in the framework of the finite-field perturbation approach. The method is used at both the SCF HF and different correlated levels of approximation. The relativistic corrections to the dipole moment of AgH are evaluated through the first-order with respect to the Cowan—Griffin perturbation operator and through the complete fourth-order with respect to the electron correlation perturbation by using many-body perturbation theory. The final predicted value of the AgH dipole moment at the experimental equilibrium bond distance (1.618 Å) is 2.86 D. A considerable correction to the SCF HF result is given by the first-order pure relativistic term. The mixed relativistic—correlation contributions are non-negligible.