Assessing the source of error in the Thomas-Fermi-von Weizsacker density functional

We investigate the source of error in the Thomas-Fermi-von Weizsacker (TFW) density functional relative to Kohn-Sham density functional theory (DFT). In particular, through numerical studies on a range of materials, for a variety of crystal structures subject to strain and atomic displacements, we find that while the ground state electron density in TFW orbital-free DFT is close to the Kohn-Sham density, the corresponding energy deviates significantly from the Kohn-Sham value. We show that these differences are a consequence of the poor representation of the linear response within the TFW approximation for the electronic kinetic energy, confirming conjectures in the literature. In so doing, we find that the energy computed from a non-self-consistent Kohn-Sham calculation using the TFW electronic ground state density is in very good agreement with that obtained from the fully self-consistent Kohn-Sham solution.

Automated summary

We investigate the source of error in the Thomas-Fermi-von Weizsacker (TFW) density functional relative to Kohn-Sham density functional theory (DFT). Through numerical studies on a range of materials, we find that the energy deviation between TFW and Kohn-Sham is caused by the poor representation of linear response in TFW approximation for electronic kinetic energy. However, using TFW electronic ground state density, the energy computed from a non-self-consistent Kohn-Sham calculation is in good agreement with that obtained from the fully self-consistent Kohn-Sham solution.