Analysis of correlation consistent wavefunctions: H 3XH bond energies (X=C, Si and Ge)

Abstract

We have analyzed the CCCI wavefunction for the calculation of bond dissociation energies. In the first part, CCCI is reexpressed as a non-orthogonal valence bond CI wavefunction which describes bond formation as the mixing of one covalent and two ionic parent configurations. Every other configuration is considered as an improvement of one of these three building blocks. They are grouped into different classes, the contribution of which are successively analyzed. We found the dynamical correlation of ionic structures (only one for a polar bond such as HSiH 3 or HGeH 3) to be of prime importance in obtaining accurate dissociation energies. In the second part, we improve CCCI by extending both the one- and N-electron bases, which lead to an increase and decrease of the computed bond energies, respectively. We thus conclude that the high accuracy of CCCI at the DZP level results from a cancellation of limited errors. The highest level used is uniformly accurate and yields D e of 110.9, 96.3 and 92.5 kcal/mol for CH 4, SiH 4 and GeH 4 respectively.