Breit-Pauli and direct perturbation theory calculations of relativistic helium polarizability

Large Gaussian-type geminal wave function expansions and direct perturbatio n theory (DPT) of relativistic effects have been applied to calculate the r elativistic contribution to the static dipole polarizability of the helium atom. It has been demonstrated that DPT is superior for this purpose to tra ditional Breit-Pauli calculations. The resulting value of the molar polariz ability of He-4 is 0.517254(1) cm(3) mol(-1), including a literature estima te of QED effects. As a by-product, a very accurate value of the nonrelativ istic helium second hyperpolarizability, gamma = 43.104227(1) atomic units (without the mass-polarization correction), has been obtained.