The pairwise correlated generalized valence bond model of electronic structure. III. Photoionization of the helium atom

The calculation of photoionization cross sections for the helium atom provides a simple but sensitive test of the accuracy of correlated wavefunctions and has been used to evaluate the relative importance of orbital splitting and dynamic electron correlation. We find that although dynamic correlation has a greater effect on the total energy, orbital splitting has a greater effect on the transition probabilities. However, if we wish to reduce the errors in calculated transition probabilities below 10%, we must include both orbital splitting and dynamic electron correlation. The pairwise correlated generalized valence bond wavefunction, which includes both effects, gives transition probabilities with errors of about 1%.