COMPUTER-SIMULATION OF THE STRUCTURE AND STABILITY OF FORSTERITE SURFACES

The aim of this paper is to demonstrate that atomistic simulations can be used to evaluate the structure of mineral surfaces and to provide reliable data for forsterite surfaces up to a plane index of 2 using t he code METADISE. The methods used to calculate the surface structure and energy which have more commonly been used to study ceramics are br iefly explained as is a comparison with experimental data, most notabl e the crystal morphology. The predicted morphologies show that all the methods (Donnay-Harker, Attachment energies and equilibrium) show mos t of the surfaces that are expressed in observed crystals. The equilib rium morphology calculated from the relaxed surface energies is the on ly method which expresses the {201} surfaces and the {101} surfaces, w hich appear only upon relaxation. The more stable surfaces are shown t o be those which have the highest surface density and more closely res emble close packed structures with highly coordinated surface ions and silicon as far from the surface as possible. The most stable surfaces the {100} which has alternating layers of MgO and SiO2 terminating wi th an MgO layer. The structure is similar to the MgO {100} surfaces an d has a similar energy (1.28 Jm(-2) compared to 1.20). The second most stable are the {201} which have a stepped surface topology, but is al so compact with a relaxed surface energy of 1.56 Jm(-2). The results i ndicate that atomistic simulation is well suited to the prediction of surface structure and morphology although care must be taken in choosi ng potentials which model the structure and elastic properties accurat ely.