Reactive symbol sequences for a model of hydrogen combustion

Abstract

Transient, macroscopic states of chemical disequilibrium are born out of the microscopic dynamics of molecules. As a reaction mixture evolves, the temporal patterns of chemical species encodes some of this dynamical information, while their statistics are a manifestation of the bulk kinetics. Here, we define a chemically-informed symbolic dynamics as a coarse-grained representation of classical molecular dynamics, and analyze the sequences of chemical species for a model of hydrogen combustion. We use reactive molecular dynamics simulations to generate the sequences and derive probability distributions for sequence observables: the reaction time scales and the chain length - the total number of reactions between initiation of a reactant and termination at products. The time scales and likelihood of the sequences depend strongly on the chain length, temperature, and density. Temperature suppresses the uncertainty in chain length for hydrogen sequences, but enhances the uncertainty in oxygen sequence chain lengths. This method of analyzing a surrogate chemical symbolic dynamics reduces the complexity of the chemistry from the atomistic to the molecular level and has the potential for extension to more complicated reaction systems.

Benchmarking the Performance of the ReaxFF Reactive Force Field on Hydrogen Combustion Systems

“…While these results appear to be a condemnation of ReaxFF methods for these systems, studies by both the developers ,− ,,,,,− ,,− ,− and users − ,,,,,− ,,, have demonstrated the utility of ReaxFF as an exploratory tool for atomistic simulation. We also acknowledge the difficulty of parameter training for the ReaxFF system.…”

“…While these results appear to be a condemnation of ReaxFF methods for these systems, studies by both the developers 39,[51][52][53][54][55]57,58,61,63,[67][68][69][70][71][72]74,[76][77][78][79][80][81][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97] and users [31][32][33][34]56,59,60,62,[64][65][66]73,75,…”

“…A more complete review of the history, current standings, and challenges of modeling H 2 combustion is given in the discussion of their work. 30 Three of us [31][32][33][34][35][36] have recently developed and applied a method of reactive symbol sequences to the study of hydrogen combustion as an alternative route to analyze chemical kinetics. This framework avoids the ideas of elementary reactions and rate coefficients, both of which can be strongly dependent on modeling assumptions.…”

Photophysical Properties of Nitrated and Halogenated Phosphorus Tritolylcorrole Complexes: Insights from Theory

“…No symmetry constraints were imposed during the geometry optimizations. On the basis of our previous experience of the photophysical properties of similar systems [ 33 , 34 , 35 , 36 ], ground and excited state optimization were performed by using the B3LYP [ 37 , 38 ] exchange and correlation functional coupled with the 6-31G* basis sets for all the atoms excepts for iodine for which the SDD pseudopotential [ 39 ] was employed.…”

Initiation mechanisms and kinetic analysis of the isothermal decomposition of poly(α-methylstyrene): a ReaxFF molecular dynamics study

“…In particular, the ReaxFF reactive force eld, originally developed by van Duin and colleagues in 2001, has been successfully utilized for modeling a wide variety of chemical reactions including explosion of high-energy materials, combustion of fuel, and thermal decomposition of polymers. 7,[17][18][19][20][21][22][23][24][25] Compared with the high computational cost of quantum chemistry methods, it is signicantly reduced in reactive MD simulations. However, under realistic experimental conditions, thermal decomposition reactions are observed within hours or even days, which is many orders of magnitude larger than the typical MD time scales.…”