Comparison of semi-empirical and ab initio calculations of the mixing properties of MO-M ' O solid solutions

Theoretical predictions of the mixing properties of solid solutions can be made, in principle, via three different approaches: through the use of phen omenological, semi-classical atomistic, and ab initio techniques. Compariso n of the results, obtained by application of all of the above-mentioned way s, 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 in ferred that the predicted mixing energies for the whole range of compositio ns are generally in reasonable agreement with each other and with available experimental measurements for the systems under consideration. However, cl oser inspection shows marked systematic differences between the values of m ixing energy and the structure relaxation parameters predicted with the use of different methods. In particular, this is due to the use of rather smal l and ordered unit cells for the atomistic and ab initio calculations. This allows one to make approximate estimates of disordering energies and propo se some ways to improve the theoretical simulation of the solid solutions' mixing properties. (C) 2000 Academic Press.