題目：Reaction Coordinate Identification and Rates of Methane Hydrate Nucleation from Molecular Dynamics Simulations
Understanding the molecular mechanism of clathrate hydrate formation has been a challenging and fundamental research topic for many years. Recently, molecular simulations of clathrate hydrates have significantly advanced our understanding of the kinetics and pathway for hydrate nucleation from solution. The simulations reveal the formation of clathrate structures from multi-phase systems. Here we extract mechanistic details to define a reaction coordinate associated with specific molecular events that precede nucleation, reach a critical size, and result in growth. After defining this reaction coordinate for methane hydrate, advanced sampling methods are used to calculate a kinetically meaningful free energy pathway. Specifically, we will discuss the “Mutually Coordinated Guest” order parameter, its usage to estimate a hydrate nucleus critical size, testing of the order parameter via pB histogram shooting, and equilibrium path sampling calculations to determine the reaction coordinate and free energy change along the reaction coordinate. Optimization and use of a reaction coordinate is essential for the quantification of clathrate hydrate nucleation and growth. With a proven RC in hand for methane hydrate, a path forward is available for work involving heterogeneous nucleation, ethane hydrate nucleation, or inhibited systems at moderate conditions.