Limited configuration interaction calculations of one-electron properties: the use of a window

Abstract

The purpose of this study is to determine a way of routinely calculating one-electron properties, with a high degree of accuracy, for systems of considerable size, i.e. consisting of ten or more second-row elements. A limited form of a Configuration Interaction calculation with Single and Double excitations (CISD) using the 6–31 ++G(d,p) basis is chosen. The quality of a set of calculated one-electron properties is investigated as a function of the number of Molecular Orbitals (MO) considered. All values are compared with the results of CISD calculation using the Frozen Core approximation (CISD(FC)) as a reference calculation. About 80% of the CISD(FC)-correlation energy for the test-systems SCN −, CH 2CHO −, NO − 2 and H 2O is recovered when performing a CISD calculation limited by using only about 50% of all CSFs possible. In general, the values of the dipole moment and the electronic spatial extent, the one-electron properties investigated, are found to be close to the reference values.