Calculation of frequency-dependent hyperpolarizabilities using general coupled-cluster models

By exploiting the similarities between response theory and analytic derivative theory, we present a scheme for calculating frequency-dependent hyperpolarizabilities at the coupled-cluster level within the framework for analytic third derivatives. This has been implemented for arbitrary levels of coupled-cluster theory up to the full-configuration-interaction limit. An investigation of some small molecules shows that the inclusion of triple excitations is essential for an accurate description of hyperpolarizabilities. (C) 2007 American Institute of Physics.