Degenerate Perturbation Theory for Electronic g Tensors:Leading-Order Relativistic Effects

摘要

A new approach for the evaluation of the leading-order relativistic corrections to the electronic g tensors of molecules with a doublet ground state is presented.The methodology is based on degenerate perturbation theory and includes all relevant contributions to the g tensor shift up to order theta(alpha~4)originating from the one-electron part of the Breit-Pauli Hamiltonian-that is,it allows for the treatment of scalar relativistic,spin-orbit,and mixed corrections to the spin and orbital Zeeman effects.This approach has been implemented in the framework of spin-restricted density functional theory and is in the present paper,as a first illustration of the theory,applied to study relativistic effects on electronic g tensors of dihalogen anion radicals X2~-(X = F,CI,Br,I).The results indicate that the spin-orbit interaction is responsible for the large parallel component of the g tensor shift of Br2~-and l2~-,and furthermore that both the leading-order scalar relativistic and spin-orbit corrections are of minor importance for the perpendicular component of the g tensor in these molecules since they effectively cancel each other.In addition to investigating the g tensors of dihalogen anion radicals,we also critically examine the importance of various relativistic corrections to the electronic g tensor of linear molecules with SIGMA-type ground states and present a two-state model suitable for an approximate estimation of the g tensor in such molecules.