The Hessian biased force field for silicon nitride ceramics: Predictions of thermodynamic and mechanical properties for α- And β-Si ₃N₄

A force field (MSXX) for molecular dynamics simulations of silicon nitride is derived using the Hessian biased technique from ab initio calculations on N(SiH₃)₃ and Si(NH₂)₄ clusters. This is used to model the nitrogen and silicon centers of the α and β forms of crystalline Si₃N₄ for prediction of crystal structures, lattice expansion parameters, elastic constants, phonon states, and thermodynamic properties. Experimental measurements on many of these important physical constants are lacking, so that these calculations provide the first reliable data on such fundamental properties of silicon nitride. This MSXX force field is expected to be useful for molecular dynamics simulations of dislocations and grain boundaries and for studying the reconstruction and energetics of clean, reduced, and oxidized surfaces.