Time-dependent coupled-cluster calculations of polarizabilities and dispersion energy coefficients.

Time-dependent coupled cluster theory, with unrestricted electron spins and full treatment of orbital rotation, is used to calculate polarizabilities at imaginary frequencies for Li, Ar, HCl, CO, N(2), O(2), and H(2)O, and to obtain dispersion energy coefficients for their pair interactions. Results obtained with augmented quadruple-zeta basis sets agree well with the best literature values of the C(6) dispersion energy coefficients. Time-dependent coupled cluster with single and double excitations theory will be useful as a benchmark for evaluating more approximate theories. (c) 2007 Wiley Periodicals, Inc. J Comput Chem, 2008.