Virtual orbitals, excitation energies, and oscillator strengths

The method of Huzinaga and Arnau (1970, 71) for improving virtual orbitals in the Hartree-Fock is discussed from different points of view. An application to the calculation of excitation energies and oscillator strengths (f values) for the helium atom is given. The calculated excitation energies are found to be accurate to within 2 to 3%. The agreement of the calculated f values with those obtained by more sophisticated methods is remarkable.