Instantaneous structure of an MgSiO₃ melt simulated by molecular dynamics

A series of molecular dynamics (MD) calculations¹ has been carried out to visualize the atomic configuration in MgSiO₃ melt and glass. The 'computer-generated' configuration seemed to be realistic. At zero pressure the Si-O-Si angle distribution gave a clear peak at ∼145°in agreement with the result of ordinary X-ray study on vitreous SiO₂ (ref. 2). Coordination of O around Mg was irregular, because the whole structure is dominated by packing of the rather regular SiO₄ tetrahedra which are linked together by sharing O atoms at corners. The 'melt' also showed a partial conversion from a 4- to 6-coordination state on 'compression' within a reasonable density range, accompanied by a steady decrease in the Si-O-Si angles. The MD calculation, which is simply the numerical integration of the classical newtonian equations of motion for many particles in a hypothetical periodic space, has been successfully applied to various molten ionic salt systems¹. Following Woodcock et al's³ first application of MD to vitreous SiO₂, we decided to extend the MD calculation to systems of geochemical importance and report our results here.