Simulation of Chemical Reactions with Low Barriers

The techniques used by Edberg et al. 2 and Brown and Clarke are particularly useful in the study of processes in neat liquids. Statistically valid results are much more readily obtained because all the molecules where dynamics are being run can potentially undergo the relatively rare reactive event. Thus, the number of interesting events that occurs within a given simulation 

In the molecular dynamics simulations of the isomerization process, Marks et al. used 8 Ar atoms in a spherical vessel of varying size, thereby examining a large density range 10 ps of microcanonical molecular dynamics 

The reader should note that the techniques used for low barrier reactions have so far been applied only to isomerizations. The reason for this is quite simple for bimolecular reactions, one has to consider a competitive process, the diffusion of the reactants away from each other. For many reactions, this is a more likely event than climbing the barrier, and therefore interesting reactive events occur with a much smaller frequency. The techniques for simulating rare events that we shall describe in the next section bypass both this problem and the difficulty of dealing with high barriers. However, for isomerizations with barriers less than 5kT or so, the techniques we have described in this section have proven valuable in understanding the reaction process. 

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