RELATIVISTIC CORRECTIONS TO MOLECULAR DYNAMIC DIPOLE POLARIZABILITIES

Using response function methods we report calculations of the dynamic isotropic polarizability of SnH4 and PbH4 and of the relativistic corr ections to it in the random phase approximation and at the correlated multiconfigurational linear response level of approximation. All relat ivistic corrections obtained from the use of the Darwin and mass-veloc ity operators to first order are included at both levels of approximat ion. We find that correlation and relativistic contributions are not e ven approximately additive for the two molecules. The importance of th e relativistic corrections is smallest in the correlated calculations, as has also been observed for other properties. For SnH4 the correlat ion contribution and the pure relativistic correction are of the same order of magnitude, whereas for PbH4 the relativistic correction becom es more important than the correlation contribution. We report estimat ed Cauchy moments, obtained from fitting the dispersion of the calcula ted corrections as a function of omega(2). The frequency dependence of the nonrelativistic polarizability is most pronounced at the correlat ed level, mainly due to lower excitation energies in the multiconfigur ational calculations than those in the random phase approximation. (C) 1995 American Institute of Physics.