An improvement of cluster variation method entropy functional for bcc alloys

The entropy functional in the tetrahedron approximation of the cluster variation method (CVM) for the body-centered cubic structure has been modified to yield accurate consolute temperature for a phase separating system. The improvement is achieved by a change in the multiplicity of the basic tetrahedron cluster and approximately accounts for truncation errors in the entropy functional of CVM owing to finite size of the basic cluster. We demonstrate that the phase diagram, thermodynamic properties and short range order parameters show improved agreement with more accurate results, without involving additional computational burden. Hence, the modified entropy functional could be used as a standard for CVM.