Reactive Force Field Modeling of Silicate Sorption on the Hematite r-plane
Brenhin Keller, Princeton University
Passivation of iron oxide and oxyhydroxide surfaces by silicate sorption has implications for our understanding of processes such as the mobility of heavy metals in acid mine drainage and the corrosion of ferrous metals. However, due to the high activation energy for silicate sorption, individual sorption events are rare on timescales accessible by ab initio molecular dynamics, impeding computational studies. We have approached the problem using a LAMMPS ReaxFF reactive force field umbrella sampling approach for the case of silicate sorption on the hematite r-plane – a naturally occurring iron oxide surface with well-understood surface chemistry. Unlike classical molecular dynamics, reactive force field MD allows for the simulation of bond breaking and formation, but with dramatically reduced computational requirements compared to full ab initio quantum methods such as Car-Parrinello MD. Further mitigating the computational challenges of rare-event sampling, we have used a directed sampling method - umbrella sampling - which facilitates the calculation of relative free energy curves along a specified reaction coordinate and is enabled by the open-source COLVARS package. The results allow for comparison of the free energy landscape of silicate sorption for different reaction mechanisms with varying surface configurations, providing insight into the mechanism and dynamics of sorption.
Abstract Author(s): C. Brenhin Keller, Adam F Wallace, and Glenn A. Waychunas