Relativistic Effects in Molecular Calculations

Abstract

Two types of relativistic effects, which are important in molecules involving heavy atoms, are discussed: the kinematic effect resulting in a contraction of s and expansion of d shells, and the zero-field splitting due to spin-orbit interaction, which can be larger than the difference between electronic levels. The kinematic effects can be taken into account by employing the spin-free no-pair operator, the spin-orbit splitting can be evaluated by the operator in the Breit-Pauli form. Various examples for molecules such as AuH, NiH and CuO demonstrate the effect of the relativistic contributions on the properties of ground and excited molecular states.