Atomic diffusion in covalent liquids under pressure from ab initio molecular dynamics

The microscopic mechanisms of atomic diffusion in liquid GeO2 and SrGeO3 are investigated by ab initio molecular-dynamics simulations. We clarify the differences of diffusion mechanism between liquid GeO2 and SrGeO3. In both liquids, non-bridging oxygen double bonded to only one germanate plays a key role in the atomic diffusion mechanism. It is found that, in liquid SrGeO3 which has non-bridging oxygen in the equilibrium state at ambient pressure, atomic diffusion is possible without generating overcoordinated atoms at ambient pressure, while the over coordinated atoms are always needed for the formation of non-bridging oxygens in liquid GeO2. When the pressure increases, only liquid GeO2 has a diffusion maximum, which is given by, the atomic diffusion with concerted reaction gives the dif fusion maximum