Photoabsorption cross section of O, S, Se, and Te.

Photoabsorption cross sections of the ground state of four oxygen-group atoms are calculated using the eigenchannel [ital R]-matrix method. The calculation is performed in the energy range from the first to the third ionization threshold of the residual ions. The present calculations are in good agreement with experimental results except for Te. We investigate the origin for some of the generic features of the cross section. A systematic study of the convergence as a function of type of basis demonstrates the importance of the polarizability of the valence shell. The lessons learned from these atoms should be generally applicable to other columns of the periodic table.