Excitation energies from time-dependent density functional theory using exact and approximate potentials

The role of the exchange-correlation potential and the exchange-correlation kernel in the calculation of excitation energies from time-dependent densi ty functional theory is studied. Excitation energies of the helium and bery llium atoms are calculated, both from the exact Kohn-Sham ground-state pote ntial and from two orbital-dependent approximations. These are exact exchan ge and self-interaction corrected local density approximation (SIC-LDA), bo th calculated using Krieger-Li-Iafrate approximation. For the exchange-corr elation kernels, three adiabatic approximations were tested: the local dens ity approximation, exact exchange, and SIC-LDA. The choice of the ground-st ate exchange-correlation potential has the largest impact on the absolute p osition of most excitation energies. In particular, orbital-dependent appro ximate potentials result in a uniform shift of the transition energies to t he Rydberg states. (C) 2000 John Wiley & Sons, Inc.