Time dependent density functional photoionization of CH4, NH3, H2O and HF

The time dependent density functional theory (TD-DFT) and the Kohn-Sham (KS) schemes have been employed to calculate the cross section and the asymmetry parameter profiles of all the orbitals (from outer valence to core Is) of CH4, NH3, H2O and HF, employing a one centre expansion of B-spline functions. The comparison between the KS and TD-DFT results shows that the screening effects play an important role even for the first row hydrides. The comparison of the TD-DFT results with the available experimental data shows that TD-DFT gives quantitative accuracy. Well defined trends are identified along the series, with respect to the nature of the ionized orbitals. Inner valence cross section is the most difficult to be described even at the TD-DFT level, and this has been attributed to shake-up processes not considered at the present level of the theory. In general, the good accuracy of the TD-DFT method and its computational economy makes it a good candidate to application to more extended and complicated molecules. (C) 2002 Elsevier Science B.V. All rights reserved.