Reliability and applicability of magnetic force linear response theory: Numerical parameters, predictability, and orbital resolution

TL;DR

This paper evaluates the reliability of magnetic force linear response theory for calculating spin interactions, examining parameter dependence, extending the method to orbital resolution, and applying it to Fe-based superconductors to reveal orbital-specific interactions.

Contribution

It demonstrates the small parameter dependence of the method, extends it to orbital resolution, and applies it to Fe-based superconductors to analyze orbital-resolved magnetic interactions.

Findings

Parameter dependence is minimal compared to other methods.

The method provides reasonable estimates for localized moments even without ground state info.

Orbital-resolved interactions differ between pnictides and chalcogenides.

Abstract

We investigated the reliability and applicability of so-called magnetic force linear response method to calculate spin-spin interaction strengths from first-principles. We examined the dependence on the numerical parameters including the number of basis orbitals and their cutoff radii within non-orthogonal LCPAO (linear combination of pseudo-atomic orbitals) formalism. It is shown that the parameter dependence and the ambiguity caused by these choices are small enough in comparison to the other computation approach and experiments. Further, we tried to pursue the possible extension of this technique to a wider range of applications. We showed that magnetic force theorem can provide the reasonable estimation especially for the case of strongly localized moments even when the ground state configuration is unknown or the total energy value is not accessible. The formalism is extended to carry the orbital resolution from which the matrix form of the magnetic coupling constant is calculated. From the applications to Fe-based superconductors including LaFeAsO, NaFeAs, BaFe$_2$As$_2$ and FeTe, the distinctive characteristics of orbital-resolved interactions are clearly noticed in between single-stripe pnictides and double-stripe chalcogenides.