Assessment of parametrized core correlation schemes in Gaussian-3 theory

Abstract

The use of parametrized core correlation equations in Gaussian-3 (G3) theory is assessed on the G2/97 test set. Two parametrized equations for estimating core correlation effects in molecules, one based on bond order and the other on atomic number, are considered in this study. The parameters are obtained by fitting to actual calculated core correlation contributions to atomization energies. Both equations give mean absolute deviations for the G2/97 test set similar to that in original G3 theory. It is also found that use of a fit based on more accurate core correlation values from the CCSD(T) method does not improve the accuracy of G3 theory.