Padded-box model for the effect of pressure on helium

The Hartree-Fock method is applied to find the energy of the ground state of the helium atom enclosed in a spherical box with a finite potential wall. The model is used to describe the increase of the electronic kinetic energy of helium gas at high pressures. For pressures less than 25 kbar a small negative potential wall (<-0.1 Hartree) leads to significantly better agreement with experimental results than the widely used hard-box model. An approximate form of a new boundary perturbation method is applied to the enclosed helium atom and very good agreement with the SCF result is found up to pressures of the order of 1 Mbar.

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