Single-site orthogonalization for first-principles computations of exchange coupling constants

TL;DR

This paper introduces a single-site orthogonalization (SO) scheme for first-principles calculations of exchange coupling constants that reduces basis set dependence and improves convergence, enabling more accurate magnetic property predictions.

Contribution

The paper presents a novel SO scheme that enhances the accuracy and convergence of exchange coupling constants in first-principles calculations compared to existing methods.

Findings

SO scheme reduces basis set dependence of J_ij calculations.

SO scheme achieves convergence of J_ij for various magnetic materials.

SOS extension accurately predicts magnetic orders and Curie temperatures.

Abstract

For accurate first-principles computations of exchange coupling constants $J_{ij}$ by the Liechtenstein method with localized basis sets, we developed a scheme using the single-site orthogonalization (SO). In contrast to the non-orthogonal (NO) scheme, where the basis set is used to compute $J_{ij}$ without modification, and the L\"owdin orthogonalization (LO) scheme, the SO scheme exhibits much less dependence of $J_{ij}$ on the choice of the basis set. The SO scheme achieves convergence of $J_{ij}$ for bcc Fe, hcp Co, and fcc Ni with an increase in the number of the basis set, while the NO and LO schemes result in the fluctuation depending on the basis set. This improvement by the SO scheme is attributed to the removal of orbital overlaps with avoiding ill-defined single-site effective potentials. We further improve the SO scheme by introducing appropriate spin population, so that the SO with spin-population scaling (SOS) scheme can provide converged Curie temperatures for transition metals. Moreover, negative values of $J_{ij}$ for dhcp Nd and rhombohedral Sm obtained by the SOS scheme can coincide with the experimentally-found magnetic order that cannot be reproduced by positive sets of $J_{ij}$.