Cluster expansion models for Fe–Cr alloys, the prototype materials for a fusion power plant

We compare two approaches to modelling the phase stability of iron and Fe–Cr binary alloys: Cluster expansion and magnetic cluster expansion. The first, based on a cluster expansion Hamiltonian, describes the effects of configurational disorder in an alloy on its thermodynamic properties. Cluster expansion can be used for studying alloys by both equilibrium and kinetic Monte Carlo methods. The second, recently proposed, “magnetic” cluster expansion (MCE) method extends cluster expansion treatment to magnetic degrees of freedom by including magnetic moments of individual atoms as variables. MCE has a unique capability for modelling the properties of a magnetic alloy in a broad range of compositions ranging from pure ferromagnetic Fe to antiferromagnetic Cr. We describe applications of both methods to modelling various properties of candidate fusion materials.