A systematic classification of atomic integrals inabinitiomolecular orbital calculations. I. The core valence approximation molecular orbital method

摘要

A computational scheme for the systematic approximation of certain twohyphen;electron integrals inabinitiomolecular orbital calculations is described in which corendash;valence overlap distributions are expanded in terms of monocentric functions centered at the core. The integral evaluation time now varies as (Nvalence)4rather than (Ntotal)4, thus resulting in substantial saving of computer time. The method is shown to be invariant to unitary transformations of the basis set and to be capable of yielding wave functions to any required accuracy. For most purposes a level of approximation denotedB1 is found to be adequate, yielding molecular energies accurate to 10minus;3a.u. with no appreciable error in other molecular properties.