Monte Carlo simulations of ternary solid solutions of key petrological and technological importance.

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This project is focused on the development of realistic activity-composition models and the calculation of temperature-pressure-composition diagrams of multicomponent solid solution phases such as aluminosilicate and majoritic garnets, Fe3+- and K-bearing omphacitic pyroxenes and Eu-bearing powellites and carbonates. We will also develop models of temperature-dependent disorder of A1/Si and N/O in SiA1ONs - new materials with interesting technological properties. These models will permit to increase accuracy of phase equilibrium calculations in diverse research areas such as metamorphic and mantle petrology, materials design and safety prognosis of long-term nuclear waste repository. To accomplish this tasks we will develop a _exible suite of software dedicated for computer simulations and thermodynamic modelling of ternary solid solutions. The software will be build over the General Utility Lattice Program (GULP) and our own Monte Carlo code and will allow simulation of the Boltzmann distribution of exchangeable atoms in supercells of general symmetry, size and composition. Temperature-dependent thermodynamic mixing properties of solid solution phases will be obtained from the thermodynamic integration of the Monte Carlo results. In parallel with these tasks we will develop a database of transferable empirical interatomic potentials for oxides, nitrides, carbonates and molibdates with a superior accuracy compared to those currently available. Key words: Monte Carlo simulations, ternary solid solutions.