FREQUENCY-DEPENDENT HYPERPOLARIZABILITIES IN THE BRUECKNER COUPLED-CLUSTER THEORY

A formulation for calculating frequency-dependent hyperpolarizabilitie s in the coupled-cluster (cc) theory with the Brueckner orbitals is pr esented. Our quasi-energy derivative (QED) method is applied, and expl icit expressions for response properties up to third order [mu, alpha( -omega1; omega1), beta(- omega(sigma); omega1, omega2)] are derived. T he 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-B rueckner CEPA-0 by Kutzelnigg to the time-dependent case is also discu ssed. (C) 1994 John Wiley & Sons, Inc.