Christian Neiss¹ and Christof Hättig^2
1 Institut für Nanotechnologie, Forschungszentrum Karlsruhe, P.O. Box 3640, D-76021 Karlsruhe, Germany
² Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44780 Bochum, Germany

J. Chem. Phys., 126, 154101 (2007).
(Received 31 January 2007; accepted 21 February 2007; published online 16 April 2007)

Response theory up to infinite order is combined with the explicitly correlated coupled-cluster singles and doubles model including linear-r₁₂ corrections, CCSD(R12). The additional terms introduced by the linear-r₁₂ contributions, not present in the conventional CCSD calculation, are derived and discussed with respect to the extra costs required for their evaluation. An implementation is presented up to the cubic response function for one-electron perturbations, i.e., up to frequency-dependent second hyperpolarizabilities. As first applications the authors computed the electronic polarizabilities and second hyperpolarizabilities of BH, N₂, and formaldehyde and show that the improvement in the one-electron basis set convergence known from the R12 method for ground state energies is retained for higher-order optical properties. Frequency-dependent results are presented for the second hyperpolarizability of N₂. (c) 2007 American Institute of Physics.

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