Ab initio calculation of spin fluctuation spectra using time dependent density functional perturbation theory, planewaves, and pseudopotentials

TL;DR

This paper introduces a new computational method for calculating spin fluctuation spectra using time-dependent density functional perturbation theory with planewaves and pseudopotentials, validated on transition metals.

Contribution

The authors develop and implement a self-consistent approach to compute dynamic spin susceptibility using the Sternheimer equation within the adiabatic local density approximation.

Findings

Accurate magnon dispersion relations for Fe and Ni.

Cr spin susceptibility indicates incommensurate spin density wave tendency.

Method aligns well with experimental observations.

Abstract

We present an implementation of time-dependent density functional perturbation theory for spin fluctuations, based on planewaves and pseudopotentials. We compute the dynamic spin susceptibility self-consistently by solving the time-dependent Sternheimer equation, within the adiabatic local density approximation to the exchange and correlation kernel. We demonstrate our implementation by calculating the spin susceptibility of representative elemental transition metals, namely bcc Fe, fcc Ni and bcc Cr. The calculated magnon dispersion relations of Fe and Ni are in agreement with previous work. The calculated spin susceptibility of Cr exhibits a soft-paramagnon instability, indicating the tendency of the Cr spins to condense in a incommensurate spin density wave phase, in agreement with experiment.