Ab initio study of high pressure liquid silica: electrical conductivity and structure.

Abstract:

The transport properties of silicate liquids are important for understanding the thermal evolution of giant impact targets, magma oceans, and the possibility of silicate dynamos in the early Earth and in other rocky planets. However, little is known about the electrical conductivity of silicate liquids over the relevant pressure-temperature regime. Here, we focus on silica as one of the most abundant components and a model system for understanding transport properties in silicates. We perform first principles molecular dynamics simulations over the pressure-temperature encompassing that of the early Earth, and compute the electrical conductivity via the Green-Kubo formula. The electrical conductivity of the liquid substantially exceeds that of crystalline phases at all conditions. We find that along isotherms the conductivity of silica liquid reaches a maximum near 40 percent compression, remarkably similar to the compression at which 5-fold Si-O coordination is most abundant. The conductivity decreases upon further compression. The conductivity increases rapidly with increasing temperature at all pressures. We explore the underlying physical mechanisms of the computed variations of conductivity with pressure and temperature and discuss the implications of our results for magnetic field generation in basal magma oceans.