FREQUENCY-DEPENDENT HYPERPOLARIZABILITIES IN THE BRUECKNER COUPLED-CLUSTER THEORY

A formulation for calculating frequency-dependent hyperpolarizabilities in the coupled-cluster (cc) theory with the Brueckner orbitals is presented. Our quasi-energy derivative (QED) method is applied, and explicit expressions for response properties up to third order [mu, alpha(-omega1; omega1), beta(- omega(sigma); omega1, omega2)] are derived. The position of the resonances is determined from the RPA-like equation. It is found that the pole structures are not compatible with ones of the exact response functions. An extension of the coupled Brillouin-Brueckner CEPA-0 by Kutzelnigg to the time-dependent case is also discussed. (C) 1994 John Wiley & Sons, Inc.