Ni partitioning between metal and silicate melts: An exploratory ab initio molecular dynamics simulation study

Element partitioning is a key geochemical process. While partition coefficients between phases including melts have been measured in many experimental studies, new insight into the mechanisms of partitioning may be obtained by relating partitioning to melt structure. Here, we address this problem by exploring an ab initio molecular dynamics simulation approach. Combined with the thermodynamic integration method, these simulations provide a unique way to predict simultaneously thermodynamic properties related to element partitioning and information about the molecular structure of the melt. Thus, it should be possible not only to predict the partitioning of elements, but also to provide an explanation for this behavior based on atomic structures of the coexisting phases. Using this approach, we derive from first-principles the Ni partition coefficient between a metal and a silicate melt at 2500K and ambient pressure, which is at least in qualitative agreement with experiment. Structural analysis of various (Mg,Fe,Ni)2SiO4 silicate and (Fe,Ni) metal melts reveals that the Ni partitioning is mainly determined by its structural environment in the silicate melt, whereas the coordination environments of Ni and Fe are almost indistinguishable in the metal melt. Possible strategies to improve the predictive power of the proposed approach are discussed.