Temperature Extrapolation of Molecular Dynamics Simulations of Complex Chemistry to Microsecond Timescales using Kinetic Models: Applications to Hydrocarbon Pyrolysis

Molecular Dynamics (MD) simulations are a key tool to understand the mechanism of complex chemical system and observe their outcomes in different conditions. However, such simulations are computationally expensive, which limits their timescales to the nanoseconds. This limitation is inconsequential at high temperatures, where equilibrium is reached quickly, but it is limiting at low temperatures as the complex system cannot be equilibrated within the timescale of MD simulations. In this article we develop a method to construct kinetic models of hydrocarbon pyrolysis using the information from the high-temperature high-reactivity regime. We then extrapolate this model to low temperatures, which allows for microsecond-long simulations to be performed. It is demonstrated that this approach lead to the accurate prediction of the evolution of small molecules, as well as the size and composition of long carbon chains for a wide range of temperatures and compositions. The temperature range for which the extrapolation is robust can easily be improved by adding more simulations to the training data. When compared to experimental results our kinetic model leads to similar compositional trends while allowing for more detailed kinetic and mechanistic insights.