Hartree–Fock critical nuclear charge in two-electron atoms

Electron correlation effects play a key role in stabilising two-electron atoms near the critical nuclear charge, representing smallest charge required to bind two electrons. However, deciphering importance of these relies on fully understanding uncorrelated Hartree-Fock description. Here, we investigate properties ground state wave function small limit using various symmetry-restricted formalisms. We identify where spin-symmetry breaking occurs give an unrestricted that predicts ionisation electron. also discover another closed-shell electron density detaches from nucleus, and fractional spin errors static this limit.