A SEGMENTED CONTRACTION METHODOLOGY FOR GAUSSIAN-BASIS SETS TO BE USED IN DIRAC-FOCK ATOMIC AND MOLECULAR CALCULATIONS

A segmented contraction methodology is investigated using Gaussian bas is sets generated from the Dirac-Fock Hamiltonian. Dirac-Fock-Coulomb calculations are performed using various sizes of contractions of Gaus sian basis sets for Ar, Z = 18, Xe, Z = 54 and Hg, Z = 80, Contraction s of large Gaussian function exponents (the core region) for s and p s ymmetries have little effect on the Dirac-Fock-Coulomb energy for Ar b ut have a large effect for Xe and Hg atoms. The large Gaussian functio n exponents of the d and f symmetries for intermediate and heavy atoms also allow a high degree of contraction. For the valence region a str ong contraction with these function exponents for the s, p, d and f sy mmetries is not allowed. (C) 1998 Elsevier Science B.V. All rights res erved.