On the Finite Nuclear Effect and Gaussian Basis Sets for Four-Component Dirac Hartree-Fock Calculations
In this perspective we describe an overview of Dirac Hartree-Fock theory, which is the foundation of relativistic quantum chemistry methods vital in the molecular modeling of heavy element chemistry and physics. A special emphasis was placed upon the physical connection between the finite nuclear model and the kinetic-balance condition between the large and small components. Additionally, we review the consequences of basis set choices for Dirac Hartree-Fock calculations in the restricted kinetic balance formalism, and show that the basis set limit does not have a hard lower bound due to the nature of the Hamiltonian, referred to in the literature as prolapse. Standard Gaussian basis set contraction schemes can break down in Dirac Hartree-Fock calculations, and special care must be taken for the description of core orbitals near the nucleus. The phenomena described in this perspective are vital for theoreticians and practitioners to understand when selecting a basis set for heavy element quantum chemical calculations using Dirac Hartree-Fock theory.