Geochemical reaction mechanism discovery from molecular simulation

Methods to explore reactions using computer simulation are becoming increasingly quantitative, versatile and robust. In this review, a rationale for how molecular simulation can help build better geochemical kinetics models is first given. Some common methods are summarised that geochemists use to simulate reaction mechanisms, specifically classical molecular dynamics and quantum chemical methods and their strengths and weaknesses are also discussed. Useful tools such as umbrella sampling and metadynamics that enable one to explore reactions are discussed. Several case studies wherein geochemists have used these tools to understand reaction mechanisms are presented, including water exchange and sorption on aqueous species and mineral surfaces, surface charging, crystal growth and dissolution, and electron transfer. The effect that molecular simulation has had on our understanding of geochemical reactivity is highlighted in each case. In the future, it is anticipated that molecular simulation of geochemical reaction mechanisms will become more commonplace as a tool to validate and interpret experimental data, and provide a check on the plausibility of geochemical kinetic models.