The Leading Correction to the Thomas-Fermi Model at Finite Temperature

TL;DR

This paper derives a leading quantum correction to the finite-temperature Thomas-Fermi model, scaling as Z^{-1/3}, and introduces a corrected free energy functional to improve atomic electron density and energy calculations.

Contribution

It introduces a new correction to the Thomas-Fermi model for finite temperature, accounting for strongly bound electrons, and develops a modified functional for better accuracy.

Findings

The correction scales as Z^{-1/3} and dominates other quantum corrections.

A new free energy functional incorporating the correction is proposed.

The corrected model accurately predicts electron density and energy within its validity range.

Abstract

The semi-classical approach leading to the Thomas-Fermi (TF) model provides a simple universal thermodynamic description of the electronic cloud surrounding the nucleus in an atom. This model is known to be exact at the limit of $Z\rightarrow\infty$, i.e., infinite nuclear charge, at finite density and temperature. Motivated by the zero-temperature case, we show in the current letter that the correction to TF due to quantum treatment of the strongly bound inner-most electrons, for which the semi-classical approximation breaks, scales as $Z^{-1/3}$, with respect to the TF solution. As such, it is more dominant than the quantum corrections to the kinetic energy, as well as exchange and correlation, which are known to be suppressed by $Z^{-2/3}$. We conjecture that this is the leading correction for this model. In addition, we present a different free energy functional for the TF model, and a successive functional that includes the strongly bound electrons correction. We use this corrected functional to derive a self-consistent potential and the electron density in the atom, and to calculate the corrected energy. At this stage, our model has a built-in validity limit, breaking as the L shell ionizes.