Relativistic effects on linear and nonlinear polarizabilities studied by effective-core potential, Douglas–Kroll, and Dirac–Hartree–Fock response theory

Abstract

Relativistic calculations of electric dipole moments, linear polarizabilities, and first- and second-order hyperpolarizabilities have been carried out for the isovalent group VI dihydrides (O–Po) and group VII monohydrides (F–At) at three different levels: the time-dependent Dirac–Hartree–Fock approximation, the time-dependent Hartree–Fock approximation with a Douglas–Kroll transformed one-component Hamiltonian, and the time-dependent Hartree–Fock approximation with effective-core potentials. These calculations are compared with nonrelativistic time-dependent Hartree–Fock results in order to elucidate the role of relativistic effects on these properties and to investigate the extent to which the Douglas–Kroll approach and the effective-core potentials—both of which neglect spin-dependent terms but are computationally less demanding—are able to reproduce the 4-component Dirac–Hartree–Fock results. The results show that qualitatively correct relativistic corrections in most cases can be obtained with the more approximative methods, but that a quantitative agreement with 4-component calculations is often not obtained.