Ab initio molecular-dynamics study of structural and electronic properties of liquid MgSiO3 under pressure

The structural and electronic properties of liquid MgSiO3 under pressure are investigated by ab initio molecular-dynamics simulations. At ambient pressure, most of Si atoms have the same coordination even in the liquid state as in the crystalline phase, i.e., each Si atom is bonded to two bridging oxygen (BO), i.e., O atoms twofold-coordinated to Si, and two nonbridging oxygen (NBO), i.e., O atoms onefold-coodinated to Si. It is, however, found that the structural defects, such as fivefold-or threefold-coordinated Si atoms, are always formed with the rearrangement of Si-O covalent bonds in the atomic diffusion processes. The population analysis clarifies that maximum of the diffusivity in the pressure dependence results from the increasing of the number of defects under compression.