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The Hartree perturbation method is used to calculate the dipole polarizability, the electric field at the nucleus, the quadrupole polarizability and the nuclear shielding factor of helium using a twelve-term representation of the unperturbed Hartree wave functions. It is pointed out that the method yields lower bounds for the dipole and quadrupole polarizabilities. The absolute error in the predicted values of any of the quantities is less than 4.3%.
Dalgarno et al. (Wed,) studied this question.