MARVIN - A NEW COMPUTER CODE FOR STUDYING SURFACES AND INTERFACES AND ITS APPLICATION TO CALCULATING THE CRYSTAL MORPHOLOGIES OF CORUNDUM AND ZIRCON

A new computer code (MARVIN), employing two-dimensional (2D) periodic boundary conditions, has been developed for the simulation of surfaces and interfaces. The models and methodologies incorporated within the program are discussed. The utility of the program in calculating crystal morphologies is explored using alpha-Al2O3 and zircon as examples. The important aspects of these calculations are that they include the use of covalent-type force fields in the latter potential model and that the effects of surface relaxation on the growth morphology are calculated for the first time. It is demonstrated that relaxation has a much larger effect on the equilibrium morphology than the growth morphology, but it can still be significant on the latter. A previously derived relationship between the growth and equilibrium morphologies is shown not to hold for relaxed systems. The growth morphologies are found to be in better agreement with experiment than the equilibrium morphologies since the latter overestimates the importance of high-index faces, especially after relaxation. Finally, the calculated surface relaxation for the basal plane of alpha-Al2O3 is found to be in complete agreement with Hartree-Fock ab initio calculations, verifying that the bulk potentials transfer to this surface.