Modeling Si-O bond hydrolysis with reactive potentials
Date
2020
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Publisher
University of Delaware
Abstract
The interactions that take place at the mineral-water interface are complex and dynamic, and the molecular scale details of mineral surface reactions are not well constrained. Quantum mechanical models of silicate mineral reactivity promise certain insights but are inhibited by significant time- and length-scale limitations, and classical potential models suffer further from questions of accuracy. This study assesses the ability of several empirical reactive potentials to describe the energetics of Si – O bond hydrolysis. To achieve this aim, classical well-tempered metadynamics simulations are performed to accelerate bond dissociation events and to obtain free energy landscapes for hydrolysis predicted by three ReaxFF potentials at 200°C (Manzano et al., 2012; Pitman and van Duin, 2012; Yeon and van Duin, 2016) and a Stillinger-Weber type potential at 25°C (Mahadevan and Garofalini, 2007; Lockwood and Garofalini, 2009). Activation energies estimated for these models all fall within the range of values predicted by quantum mechanical calculations, although two models fall outside the range observed for quartz dissolution. (Lockwood and Garofalini, 2009; Pitman and van Duin, 2012). Calculated free energies of reaction for all the ReaxFF potentials compare reasonably with projected van’t Hoff estimates for the neutral hydrolysis reaction at 200°C; however, the ionized hydrolysis reaction is thermodynamically preferred. The calculated free energy of reaction for the Stillinger-Weber style potential of Garofalini and co-workers compares well with the experimental value of the ionized hydrolysis reaction at 25°C and is recommended for future simulation studies on that basis.
Description
Keywords
Mineral surface reactions, Mineral-water interface, Metadynamics