DIRECT ALGORITHM FOR THE RANDOM-PHASE-APPROXIMATION

An algorithm for calculating excitation energies and transition moment s in the random-phase approximation (RPA) of the polarization propagat or is presented. The algorithm includes direct solution of the RPA eig envalue problem and direct evaluation of products of superoperator Ham iltonian matrices with excitation vectors. Given sufficient memory, on ly one integral evaluation step per iteration is needed. Illustrative calculations on the excitation energies and oscillator strengths of et hylene are presented. (C) 1996 John Wiley & Sons, Inc.