Reverse Monte Carlo Modeling of local structure using short-range and medium-range order parameters

An expansion of a pair-correlation function is introduced to express medium-rage order (MRO). The approximated correlation function is extended from conventional short-range order (SRO) parameters. SRO parameters are obtained by the conditional average of a pair-correlation function. It is demonstrated that the model can reconstruct SRO and MRO of atomic arrangements from an initial random state by Monte Carlo (MC) method. MRO parameters control cluster formations such as heterogeneous microstructures. On an approach of atomic pair- and triplet-interactions, approximated many-body interactions are estimated in the simulations. Moreover, the MC simulations are applied to ordering process on cooling in AgxTiS2 regarded as a typical two-dimensional material. Furthermore, cluster developments are visualized by the reverse MC method.