Perturbative and Variational Calculations of Light Atoms

Abstract

In this work, we use the perturbative and variational methods to calculate the bindingenergy of light atoms for the He, Be and Ne isoelectronic chains with hydrogen-like functions. These methods are usually treated for atoms with 2 electrons. Here, we investigate how they perform on atoms with more electrons, and the evolution of their accuracy in comparison with the Hartree-Fock energy. We will show that the perturbative method is no longer reliable for neutral atoms with more than four electrons (for the neutral Be, the relative error is larger than 5%). That will not be the case for the variational method, which stays consistently accurate with a relative error below 1% for all studied cases.