X. Perspectives in calculations on excited state in molecular systems

Abstract

This chapter discusses the perspectives in calculations on excited state in molecular system. There are essentially two different approaches used in excited state calculations. The first, attempts to determine wave functions and total energies for each state of interest. The second approach starts with the ground state and considers the excitation process as a perturbation of the ground state wave function due to the interaction with the electromagnetic field. These are the linear response methods. Here the excitation energies and the transition moments are computed directly, and do not have access to a wave function for the excited states. To this category belongs time dependent density functional theory and coupled cluster linear response methods.