Assessing spin-component-scaled second-order Møller-plesset theory using anharmonic frequencies

Abstract

Four common parametrisations of spin-component-scaled second-order Møller-Plesset (MP2) theory are benchmarked by calculating the anharmonic vibrational frequencies of a test suite consisting of eighteen diatomic and five small molecules. Of the four methods, the scaled opposite-spin MP2 (SOS-MP2), the variable-scaling opposite-spin MP2 (VOS-MP2) and the spin-component-scaled MP2 (SCS-MP2) methods perform statistically better than standard MP2 theory, while the spin-component scaled for nucleic bases MP2 (SCSN-MP2) performs worse. Vibrations of closed-shell diatomic molecules are slightly more accurately described by the SOS-MP2 method of Head-Gordon (εMAD=51 cm-1) than the SCS-MP2 method of Grimme (εMAD=61 cm-1) or the size-consistent parametrisation of VOS-MP2 (εMAD=54 cm-1). For open-shell diatomic molecules, the SOS-MP2 (εMAD=83 cm-1) and SCS-MP2 (εMAD=81 cm-1) methods are of similar accuracy, while VOS-MP2 is slightly better (εMAD=77 cm-1). Since the VOS-MP2 and SOS-MP2 methods tend to have smaller deviations from experiment, and they can be made computationally more economical than the SCS-MP2 or MP2 methods, we suggest that they should be the preferred ab initio method for computing vibrational frequencies in large molecules. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.