Ab initio simulations of cation ordering in oxides: application to spinel

At high temperature, MgAl2O4 spinel is stabilized by disorder of Mg and Al between octahedral and tetrahedral sites. Recent neutron experiments cover only a limited temperature range and are not sufficient to discriminate bet ween analytic models. Electronic structure calculations have been used to p arametrize on-site and short-ranged cluster potentials from a small number of disordered configuations. These potentials were then used in Monte Carlo simulations at finite temperatures to predict disordering thermodynamics b eyond the range of experimental measurements. Within the temperature range of the experiment, good agreement is obtained for the degree of order