Assessing the suitability of the Thomas-Fermi-von Weizs\"acker density functional for itinerant magnetism

TL;DR

This paper evaluates the Thomas-Fermi-von Weizsacker density functional's effectiveness in modeling itinerant magnetism, revealing significant limitations compared to Kohn-Sham DFT.

Contribution

It demonstrates the inadequacy of the TFW functional for accurately describing itinerant magnetic properties in metals.

Findings

Orbital-free results poorly match Kohn-Sham predictions.

Using TFW density with Kohn-Sham functional gives qualitative but limited quantitative agreement.

Fundamental limitations of TFW for itinerant magnetism are identified.

Abstract

We assess the ability of the Thomas--Fermi--von Weizsacker (TFW) functional within orbital-free density functional theory (DFT) to describe itinerant magnetism. Magnetic stability is evaluated through the susceptibility obtained from the second derivative of the total energy with respect to the net magnetization. Calculations are performed for the paramagnetic metals Al and Pd and the canonical ferromagnets Fe, Co, and Ni, with the results benchmarked against Kohn--Sham DFT. The orbital-free results show poor agreement with the Kohn--Sham predictions, failing to capture even the qualitative trends. Using the orbital-free ground-state density with the Kohn--Sham functional in a non-self-consistent calculation yields reasonable qualitative agreement, although the quantitative agreement remains limited. These results highlight fundamental limitations of the TFW functional for describing itinerant magnetism.