Simulation of proton exchange at the mineral water interface

Abstract

The results of fundamental environmental and technological processes such as bio- mineralization, the production of alumina and the management of mine wastes largely depend on careful controlling of the conditions at which the relevant chemical reactions occur. A remarkable example of this is calcium carbonate where in a relatively narrow range of pH there is a delicate balance of crystal growth or complete dissolution.Despite being well known experimentally, understanding the fundamental processes governing these pH-mediated reactions from a computational perspective is extremely challenging. On one side of the spectrum there are first principles molecular simulation techniques that allow for describing chemical reactions with an explicit treatment of the electrons, but the computational cost is prohibitive making it currently impossible to describe system sizes relevant for experimental comparison for sufficiently long times to converge thermodynamic averages. On the other side there is molecular mechanics simulation methods, which allows for studying systems of relatively large length and time scales, but the assumption of predefined bonding topologies prevents the modeling of chemical reactions.Multistate methods1 provide one alternative to modeling chemical reactions using a quantum-like Hamiltonian formalism. When molecular mechanics models are chosen to evaluate the Hamiltonian matrix elements, multistate methods provide a computationally tractable simulation method compared to their electronic structure counterparts. This has the additional advantage that previously derived forcefields that were carefully calibrated to reproduce the thermodynamic properties of a molecular species can be extended to include the relevant reactivity with the addition of relatively few parameters.In this presentation we report on results of multistate simulations of proton exchange at the mineral water interface with a particular focus on the isolated ions and calcite surface.