A shortcut to gradient-corrected magnon dispersion: exchange-only case★
Max Planck Institute for the Structure and Dynamics of Matter,
Luruper Chaussee 149,
2 Istituto Nanoscienze, Consiglio Nazionale delle Ricerche, Via Campi 213A, 41125 Modena, Italy
3 Department of Physics and Astronomy, University of Missouri, Columbia, Missouri 65211, USA
a e-mail: firstname.lastname@example.org
Received in final form: 22 May 2018
Published online: 1 August 2018
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 (~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.
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