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

Basis set methods for calculating dynamic polarizabilities and excitation e nergies via coupled Kohn-Sham equations within time-dependent density funct ional theory are introduced. The methods can be employed after solving the ground state Kohn-Sham equations with a fitting function approach. Successf ul applications of the methods to test molecules are presented. Coupled Koh n-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 line ar response of the electron density and the relations between the two types of coupled Kohn-Sham equations are investigated. The choice of norm functi ons associated with basis set representations of the coupled Kohn-Sham equa tions is discussed and shown to be a critical point of basis set approaches to time-dependent density functional theory. (C) 1999 American Institute o f Physics. [S0021-9606(99)30604-8].