A chemical reaction requires the activation of reactants and successful passage through transition states to products. Reactants and products are long‐lived stable (or metastable) states, whereas transition states are activated complexes that are rarely and briefly visited. This separation of timescales inherent in chemical reactions is characteristic of rare events generally, including nucleation of 1st‐order phase transitions, molecular isomerizations such as protein folding, and transport phenomena in solids and glasses.
Molecular simulation of rare events are complicated by the long waiting times for a transition to spontaneously occur. In my PhD work with Baron Peters and Joan-Emma Shea at the University of California, Santa Barbara, we developed new, simple methods for simulating rare events at the molecular level. We applied these methods to study aqueous ion-pair dissociation, vacancy diffusion in crystals, and the association of biomolecules in water.
One of my key frustrations as a PhD student was only being able to model systems at the classical level. In my postdoctoral work with Ed Maginn at the University of Notre Dame, we are integrating quantum calculations into classical simulations of condensed phases. To model CO2 reactivity in a task specific ionic liquid, we compute the change in free energy as CO2 binds to an anion via DFT and the solubility of CO2 in the ionic liquid via reaction ensemble Monte Carlo.
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