THE 4-COMPONENT RANDOM-PHASE-APPROXIMATION METHOD APPLIED TO THE CALCULATION OF FREQUENCY-DEPENDENT DIPOLE POLARIZABILITIES

The random phase approximation method based on the 4-component Dirac-C oulomb Hamiltonian is applied to the calculation of the frequency depe ndent dipole polarizabilities of water, stannane and the mercury atom. Results are compared with calculations in which relativity is treated via perturbation theory. For the lighter systems and for the static p olarizability of mercury relativistic perturbation theory works well. However, for the heavier systems, Hg in particular, it fails to give t he right relativistic correction to the frequency dependence of the po larizability. (C) 1997 Elsevier Science B.V.