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 basis sets generated from the Dirac–Fock Hamiltonian. Dirac–Fock–Coulomb calculations are performed using various sizes of contractions of Gaussian basis sets for Ar, Z=18, Xe, Z=54 and Hg, Z=80. Contractions of large Gaussian function exponents (the core region) for s and p symmetries have little effect on the Dirac–Fock–Coulomb energy for Ar but have a large effect for Xe and Hg atoms. The large Gaussian function exponents of the d and f symmetries for intermediate and heavy atoms also allow a high degree of contraction. For the valence region a strong contraction with these function exponents for the s, p, d and f symmetries is not allowed.