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

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.