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Connectivity-based parallel replica dynamics method for simulating chemically reactive systems using ReaxFF reactive force field method

Kaushik Joshi (Penn State University), Adri van Duin (Pennsylvania State University), Sumathy Raman (ExxonMobil)

From Atomistics to Reality: Spanning Scales in Simulations and Experiments Symposium A

Mon 9:00 - 10:30

CIT 165

Many chemical reactions have relatively high activation energies putting them beyond the time-scale of the conventional molecular dynamics (MD) algorithms at modest temperatures. One way of tackling this time-scale issue is to perform the MD simulations at elevated temperatures using the reactive force field methods such as ReaxFF [1]. However, elevated temperatures favor entropically favored reactions thereby changing the product distribution compared to low temperature chemistry. In order to capture the low temperature chemistry in atomic scale simulations, we implemented parallel replica dynamics (PRD) method [2] together with reactive force field and developed a new “event detection scheme” that allows us to simulate longer timescales, essentially up to a microsecond. In the newly developed event detection scheme, events are identified using a near-neighbor list accounting for a change in connectivity to any atom. The presentation will cover the implementation and results from the PRD simulations on pyrolysis of n-heptene and kerogen fragment at different densities and highlight the challenges in achieving high parallelization efficiency with PRD and opportunities for its improvement. [1] van Duin, A. C. T., Dasgupta, S., Lorant, F., and Goddard, W. A., 2001 “ReaxFF: A reactive force field for hydrocarbons”, Journal of Physical Chemistry A, 105, 9396-9409. [2] Voter, A., 1998, “Parallel replica method for dynamics of infrequent events”, Physical Review B, 57, 985