Monte Carlo Simulations of Mg(A1)O Solid Solutions Based on Crystal Chemical Rules

A new computational approach to modeling crystal structures based on the bond valence method is presented. The Monte Carlo technique is used to determine the atomic structure of perfect and defective crystals in accordance with crystal chemical valence sum and bond network rules. Using this method, the calculated MgO (001) surface relaxation was less than 1% of the interlayer spacing, a value that is consistent with experimental data and the results of other computational studies. The effects of Schottky defects and Al(II1) impurities on the atomic relaxations at the MgO surface were determined in separate simulations. A Mg(A1)O solid solution with a Mg:A1 ratio of 51, similar in composition to experimentally prepared calcined hydrotalcites, was also simulated, both in bulk form and with free surfaces. In agreement with experiment, simulation results indicated that Al(II1) segregates to the surface. Further analyses of the simulation results are discussed with respect to surface reactivity, surface structure, and defect formation.