Continuous Displacement Cluster Variation Method in Fourier Space

Abstract

The diffuse scattering spectra originated from both short range order and local atomic displacements for a binary alloy in a two dimensional square lattice are calculated within the realm of Continuous Displacement Cluster Variation Method (CDCVM). The key ingredient of the present scheme is to regard a displaced atom as a distinguished species and to reduce the displacement spectrum to the Short Range Order Diffuse Intensity (SROI) for a multicomponent alloy. The peak of the diffuse intensity appears at the wave vector (1/2, 1/2). By comparing with the SROI calculated by the conventional Cluster Variation Method (CVM), it is realized that the majority of the intensity originates from the contribution of short range order configurational fluctuation. The topology of the intensity distribution of the present result is similar to that derived by the conventional CVM, however the magnitude of the peak intensity differs. This is due to the fact that the directionalily of the atomic displacement is averaged out and is renormalized in the present calculation.