A model for the computer simulation of chemical reactions in the condensed phase

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Abstract
Molecular dynamics calculations have been performed on small numbers of atoms (4-64), contained within a deformable boundary, with a view to developing a model suitable for simulating chemical reactions in the condensed phase. To determine how realistic the model is, a series of standard thermodynamic quantities have been evaluated. Velocity distributions have been determined during the course of individual simulations as a function of temperature and number of atoms. For 16 atoms or more, these distributions compare very favourably with a Maxwellian distribution. An effective pressure has been calculated by two methods, one using a virial of the internal forces and another in which the forces exerted by an external container have been calculated. In the case of the latter there is a lengthy induction period before the pressure stabilizes. For 64 argon atoms at 100 K, a calculated PV curve shows evidence of condensation. For the same number of atoms at 200 K, the PV curve fits a van der Waals expression whose constants are close to experimental values. The model has been tested on the formation and decomposition of Xe2 in an argon heat bath, and the calculated equilibrium constant for Xe dimerization compares favourably with that deduced from statistical mechanics.

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