Density- and density-matrix-based coupled Kohn–Sham methods for dynamic polarizabilities and excitation energies of molecules

Abstract

Basis set methods for calculating dynamic polarizabilities and excitation energies via coupled Kohn–Sham equations within time-dependent density functional theory are introduced. The methods can be employed after solving the ground state Kohn–Sham equations with a fitting function approach. Successful applications of the methods to test molecules are presented. Coupled Kohn–Sham methods based on the linear response of the Kohn–Sham density matrix are derived from the standard coupled Kohn–Sham equation based on the linear response of the electron density and the relations between the two types of coupled Kohn–Sham equations are investigated. The choice of norm functions associated with basis set representations of the coupled Kohn–Sham equations is discussed and shown to be a critical point of basis set approaches to time-dependent density functional theory.