A shortcut to gradient-corrected magnon dispersion: exchange-only case

TL;DR

This paper introduces a simple gradient correction method at the exchange-only level to improve ab initio calculations of magnon dispersion, significantly reducing overestimated magnon stiffness in ferromagnetic materials like cobalt and nickel.

Contribution

It proposes a straightforward gradient correction approach to enhance the accuracy of magnon dispersion calculations beyond the ALDA approximation.

Findings

Gradient correction reduces magnon stiffness by about 30%.

Improves agreement between theoretical and observed magnon stiffness in cobalt and nickel.

Correction consistently decreases magnon stiffness across studied materials.

Abstract

Ab initio calculations of the magnon dispersion in ferromagnetic materials typically rely on the adiabatic local density approximation (ALDA) in which the effective exchange-correlation field is everywhere parallel to the magnetization. These calculations, however, tend to overestimate the "magnon stiffness", defined as the curvature of the magnon frequency vs. wave vector relation evaluated at zero wave vector. Here we suggest a simple procedure to improve the magnon dispersion by taking into account gradient corrections to the ALDA at the exchange-only level. We find that this gradient correction always reduces the magnon stiffness. The surprisingly large size of these corrections ($\sim 30\%$) greatly improves the agreement between the calculated and the observed magnon stiffness for cobalt and nickel, which are known to be overestimated within the ALDA.