LIMITED CONFIGURATION-INTERACTION CALCULATIONS OF ONE-ELECTRON PROPERTIES - THE USE OF A WINDOW

The purpose of this study is to determine a way of routinely calculati ng one-electron properties, with a high degree of accuracy, for system s of considerable size, i.e. consisting of ten or more second-row elem ents. A limited form of a Configuration Interaction calculation with S ingle and Double excitations (CISD) using the 6-31++G(d,p) basis is ch osen. The quality of a set of calculated one-electron properties is in vestigated as a function of the number of Molecular Orbitals (MO) cons idered. All values are compared with the results of a CISD calculation using the Frozen Core approximation (CISD(FC)) as a reference calcula tion. About 80% of the CISD(FC)-correlation energy for the test-system s SCN-, CH2CHO-, NO-2 and H2O is recovered when performing a CISD calc ulation limited by using only about 50% of all CSFs possible. In gener al, the values of the dipole moment and the electronic spatial extent, the one-electron properties investigated, are found to be close to th e reference values.