Molecular dynamics simulations of interdiffusion in MgSiO3-Mg2SiO4 melts

Molecular dynamics simulations based on ab initio interatomic potentials have been performed to study the kinetics and mechanisms of interdiffusion in MgSiO₃ and Mg₂SiO₄ melts. Diffusion coefficients in the presence of a concentration gradient are lower than self-diffusion coefficients due to the requirements of local charge-balance within the system. Extrapolations of Mg²⁺ diffusion coefficients obtained at high temperatures (5000 to 3000 K) into geologically relevant temperatures (1500 to 2500 K) are reasonably accurate compared to experimental Mg²⁺ diffusion coefficients in a compositionally similar system. A significant system-size effect is also observed on the rates of diffusion obtained from the molecular dynamics simulations. Diffusion mechanisms involve movement of individual Mg²⁺ and O^2- ions and anionic SiO_n]^(4–2n) complexes for both self-diffusion and interdiffusion.