Fermi-Amaldi model for exchange-correlation: atomic excitation energies from orbital energy differences

Motivated by recent work on asymptotic correct exchange-correlation potentials, this paper investigates properties of the Fermi-Amaldi model for the exchange-correlation potential. It compares atomic excitation energies for Hydrogen through Argon to orbital energy differences computed using the exact Kohn-Sham potential and the Fermi-Amaldi approximation to the Kohn-Sham potential. While the Fermi-Amaldi model is not a particularly good model for the exchange-correlation energy, its eigenvalue spectrum is semi-quantitatively correct for alkali metals and alkaline earths. However, it is not accurate for p-block atoms, which suggests that the Fermi-Amaldi model may not be a superior choice for asymptotically correcting exchange-correlation potentials. It is suggested that asymptotic correction involving the Fukui function would give better results.