On the high accuracy of mp2-optimised geometmes and harmonic frequencies with large basis sets

Abstract

An efficient procedure for the calculation of second derivatives of the energy at the closed-shell second-order Móller-Plesset (MP2) level of accuracy is described. The method is applied to H 2O, NH 3, H 2CO and HCN using large (TZ+2P or better) basis sets. For this set of molecules the accuracy of the optimised geometries is for single bonds ±0.002 Å, multiple bonds ±0.01 Å, angles ±0.2° and the mean error of the harmonic frequencies is 1.5%.