We have carried out equilibrium molecular dynamics simulations of MgOSiO2 mixtures with compositions continuously ranging from 20 to 80 mol.% MgO using Born-Mayer-type pairwise interaction potentials. Enthalpies of mixing, self-diffusion and mutual diffusion coefficients, shear viscosities, radial distribution functions and infrared absorption spectra were calculated. Self-diffusion coefficients determined at various pressures and temperatures ranging from 3500 to 5000 K increase significantly with greater amounts of MgO. The compositional increase of the mutual diffusion coefficient is less pronounced. The calculated compositional dependence of shear viscosity differs significantly from that expected from Stokes-Einstein or Eyring relationships. Computed radial distribution functions, velocity autocorrelation functions, and infrared absorption spectra allow for the monitoring of changes in melt structure with varying composition.
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We are indebted to Professor Bernard J. Wood for suggesting the idea of investigating mixtures of varying compositions. We thank Alain Trial and Frank Spera for helpful comments on diffusion. The authors profited from stimulating discussions with Dr. Mikhail Ya. Frenkel. This research has been supported by the National Science Foundation and the Army Research Office contract number DAALO3-89-C-0038 with the University of Minnesota Army High Performance Computing Research Center. J.R.R. is grateful for the support of a High Performance Computing Fellowship from the Army High Performance Computing Research Center.