Atomistic computer modeling of the local structure and properties of mixing of the solid solution grossular-uvarovite
The original method of atomistic computer modeling of solid solutions was applied for the study of mixing properties and local structure in the isomorphic system of garnets of row grossular Са 3Al 2[SiO 4] 3 — uvarovite Са 3Cr 2[SiO 4] 3. Parameters of interatomic potentials for the extreme members of the row have been optimized using experimental data on the structural, elastic and thermodynamic characteristics of these minerals. Optimized system of potentials properly described elastic, structural and thermodynamic properties of grossular and uvarovite and evaluate energy of point defects in the crystal structures. Calculations of the properties of mixing and the local structure for seven different compositions of the solid solution were carried out on the supercomputer SKIF «Chebyshev» MSU in the supercell 2×2×4 structure type garnet containing 2560 atoms. Mixing properties such as the enthalpy of mixing, the interaction parameters, the excess volume of mixing, the deviations from additivity of bulk modulus, vibrational and configuration contribution to the entropy of mixing were identified. It is possible to estimate the field of stability of the solid solution grossular — uvarovite. Histograms of interatomic distances M–O (M = Ca, Al, Cr, Si) and O–O in supercell were constructed and values of parameter of relaxation and changes in volume of the octahedra CrO 6 and AlO 6 were assessed. Simulation data are in good agreement with the available experimental information on this system and significantly complement it.