The influence of configurational interaction on the theoretical values of the polarizability of helium

The unperturbed ground-state wave function of helium is expressed in terms of functions arising from different configurations using the work of Taylor & Parr (1952). It is shown how the field-dependent part of the perturbed wave function can be constructed from functions of the right symmetry using the perturbing potential and the ground-state configurational functions containing variable parameters, which have their best values chosen by a variational method. With the successive addition of configurations there is a satisfactory convergence from the lower side towards the true value of the polarizability. The method should be suitable for any wave function constructed from configurations.