The pressure effect on silicon self-diffusion in the perovskite was investigated. The viscosity variation of MgSiO3 perovskite in the lower mantle was derived using the Nabarro-Herring model. In the molecular dynamics calculation, spontaneous jumping of atoms by self-diffusion was reproduced without using artificial forces, and the consistency of migration enthalpy with experimental data was improved. The results showed that the migration enthalpy increased monotonically with increasing pressure. The viscosity of MgSiO3 perovskite in the lower mantle increased monotonically with increasing depth. The obtained depth profile was distinguishable from that of MgO periclase and could be used to determine which mineral dominated lower-mantle rheology. Depending upon the assumed shape of the depth profile for lower mantle viscosity, the predominant mineral was considered to be MgSiO3 perovskite for the monotonic shape case or MgO periclase for the hill shape case that had the highest-viscosity zone in the middle of the lower mantle.

Silicon Self-Diffusion of MgSiO3 Perovskite by Molecular Dynamics and Its Implication for Lower Mantle Rheology. Ito, Y., Toriumi, M.: Journal of Geophysical Research B, 2010, 115[12], B12205