LCAO-MO-SCF calculations using Gaussian basis functions. X. AlLi-SCF results and implications for choosing configurations for configuration interaction calculations

Abstract

Ab initio LCAO-MO-SCF calculations have been performed for the lowest 1Σ+ state of AlLi. The results give a potential curve indicative of a chemically bound species but with the ESCF minimum lying slightly above the sum of the comparable SCF energies of the separated atoms. Analysis of the probable correlation energy contributions and an estimate of their magnitudes leads to an estimate of −1.5 eV for the correlation energy contribution to the binding in AlLi. This should be sufficient to permit the AlLi species to exist. The Li in AlLi is electron deficient compared to the Li atom itself. An examination of population analysis results for unoccupied orbitals leads to interesting insight into which virtual orbitals will correlate certain specific electron pairs or certain of the occupied molecular orbitals. The relationship suggests a very logical and systematic method for helping to choose a priori the best truncated set of virtual orbitals for configuration interaction calculations.