Jun Yang^a) and Christof Hättig^b)
Lehrstuhl für Theoretische Chemie Ruhr, Universität Bochum, Universitätsstrasse 150, D-44801 Bochum, Germany

J. Chem. Phys., 131, 074102 (2009).
(Received 9 June 2009; accepted 21 July 2009; published online 17 August 2009)

Coupled-cluster response theory for frequency-dependent optical properties within the coupled-cluster singles-and-doubles model (CCSD) has been derived and implemented for ansatz 2 of the explicitly correlated CCSD(R12) and CCSD(F12) methods as part of the program package DALTON. The basis set convergence of static dipole moments, polarizabilities, and parallel averages of first and second hyperpolarizabilities has been investigated for Ne, BH, N₂, CO, and BF. The frequency-dependent results are presented for the electronic second-harmonic generation of N₂. With triple-ζ basis sets, the CCSD(F12) correlation contributions using ansatz 2 are close to the basis set limits for dipole moments and second hyperpolarizabilities; the CCSD(R12) results are better than the CCSD results obtained with at least quintuple-ζ basis sets for polarizabilities and first hyperpolarizabilities. The exponent of Slater-type correlation factor for CCSD(F12) ground state energy may not be optimal and has to be re-examined for response properties. We also suggest that the remaining one-electron basis set errors arising within the coupled-cluster singles should be reduced by allowing excitations into the auxiliary orbital space.

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