Comparison of Semi-Empirical and Ab Initio Calculations of the Mixing Properties of MO–MO Solid Solutions

Theoretical predictions of the mixing properties of solid solutions can be made, in principle, via three different approaches: through the use of phenomenological, semi-classical atomistic, and ab initio techniques. Comparison of the results, obtained by application of all of the above-mentioned ways, is carried out for an example of the oxide solid solutions with the NaCl-type structure: CaO-MgO, CaO-MnO, MnO-NiO, and MgO-MnO. From this it is inferred that the predicted mixing energies for the whole range of compositions are generally in reasonable agreement with each other and with available experimental measurements for the systems under consideration. However, closer inspection shows marked systematic differences between the values of mixing energy and the structure relaxation parameters predicted with the use of different methods. In particular, this is due to the use of rather small and ordered unit cells for the atomistic and ab initio calculations. This allows one to make approximate estimates of disordering energies and propose some ways to improve the theoretical simulation of the solid solutionsʹ mixing properties.