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

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. (C) 2002 American Institute of Physics.