Conversion of magnetic freedoms into atomic configurational freedoms within the Cluster Variation Method

TL;DR

This paper extends the cluster variation method to include magnetic freedoms, allowing for the analysis of magnetic moments and spin directions, and applies it to predict the Curie temperature of nickel.

Contribution

The paper introduces a novel extension of the cluster variation method to incorporate magnetic degrees of freedom, bridging atomic displacements and magnetic moments.

Findings

Successfully applied to pure Ni

Predicted Curie temperature using electronic-structure data

Extended CVM framework for magnetic systems

Abstract

The continuous displacement cluster variation method (CDCVM) has introduced local atomic displacements into the theoretical framework of the cluster variation method (CVM) by viewing an atom displaced from a Bravais lattice point as a particular atomic species located at the lattice point. This idea of conversion from a freedom of local displacements into configurational freedom is extended in this paper to magnetic freedoms. Various magnitudes of local magnetic moments are considered, as well as two spin directions, on up-spins and down-spins. The approach is applied to pure Ni and its Curie temperature is explored with the entropy formula of the tetrahedron approximation in the CVM, using the first-nearest-neighbor pair interaction energies extracted from the total energies of various spin configurations, which are estimated from electronic-structure calculations.