Limits and accuracy of valence force field models for InxGa1-xN alloys

Formation energies, equilibrium geometries, and elastic properties of ordered In_xGa_1-xN structures have been calculated employing density funcional theory. Based on these results, limits and accuracy of several valence force field (VFF) models are compared. While these empirical models have been shown to work reasonably well to describe zincblende III/V semiconductors we find significant deviations for group III nitrides (GaN, InN) and their alloys. We therefore propose a new model that correctly takes into account the long-range electrostatic interactions. Although only the elastic constants of the binary zincblende compounds and the formation energy difference to wurtzite are used as input, the model correctly describes the formation energies and structure of wurtzite binary compounds and ternary alloys.