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-Coulomb Hamiltonian is applied to the calculation of the frequency dependent 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 polarizability of mercury relativistic perturbation theory works well. However, for the heavier systems, Hg in particular, it fails to give the right relativistic correction to the frequency dependence of the polarizability.