Analytic molecular Hessian calculations for CC2 and MP2 combined with the resolution of identity approximation

Daniel H. Friesea, Christof Hättiga, and Jörg Koßmannb
a Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, D-44801 Bochum, Germany b Atomistic Modelling and Simulation, ICAMS, Ruhr-Universität Bochum, D-44801 Bochum, Germany

J. Chem. Theory Comput., 9, 1469-1480 (2013)
(Received 15th January 2013; accepted 14th Febuary 2013)

An implementation of analytic second derivatives for the approximate coupled cluster singles and doubles model CC2 and for second-order Møller-Plesset perturbation theory (MP2) will be presented. The RI approximation for the two-electron repulsion integrals is used to reduce memory demands, operation count and I/O requirements. During the calculation the storage of \mathcal N4 quantities (where N is a measure for the system size) can completely be avoided. It is shown that with the MP2 method and an appropriate scaling of the harmonic frequencies especially C--F stretch frequencies are reproduced much better in comparison to experiment than with the B3LYP density functional. Similar advantages are observed for molecules with strong, internal van der Waals-interactions. Spin scaling offers additional improvements in these cases. The implementation has been tested for molecules with up to 81 atoms and 684 basis functions.

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