Spin-component scaled second-order Moller-Plesset perturbation theory for the calculation of molecular geometries and harmonic vibrational frequencies

The implementation and performance of an analytic gradient with respect to nuclear displacements for the spin-component scaled MP2 method (SCS-MP2) is presented. The geometries and vibrational frequencies of a benchmark set of 31 first-row molecules are considered. The new SCS-MP2 method performs significantly better than standard MP2: the RMS deviation (mean absolute error) for bond lengthsdrops from 1.2 (0.8) to 0.9 (0.6) pm and from 84 (67) to 57 (48) cm(-1) for the vibrational frequencies. As further tests the geometries of weakly bonded systems, transition metal compounds and organic transition states are considered. For almost all systems the SCS-MP2 method outperforms the MP2 approach albeit for the same computational cost. Significant improvements are especially observed for cases which are usually known as MP2 pitfalls. (C) 2004 Elsevier B.V. All rights reserved.