Computer simulation of the structure and stability of forsterite surfaces

Abstract

 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 the code METADISE. The methods used to calculate the surface structure and energy which have more commonly been used to study ceramics are briefly explained as is a comparison with experimental data, most notable the crystal morphology. The predicted morphologies show that all the methods (Donnay-Harker, Attachment energies and equilibrium) show most of the surfaces that are expressed in observed crystals. The equilibrium morphology calculated from the relaxed surface energies is the only method which expresses the {201} surfaces and the {101} surfaces, which appear only upon relaxation. The more stable surfaces are shown to be those which have the highest surface density and more closely resemble 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 with an MgO layer. The structure is similar to the MgO {100} surfaces and 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 also compact with a relaxed surface energy of 1.56 Jm⁻². The results indicate that atomistic simulation is well suited to the prediction of surface structure and morphology although care must be taken in choosing potentials which model the structure and elastic properties accurately.