Reactive canonical Monte Carlo

Abstract

A new simulation technique is developed for calculating the properties of chemically reactive and associating (hydrogen bonding, charge transfer) systems. We call this new method reactive canonical Monte Carlo (RCMC). In contrast to previous methods for treating chemical reactions, this algorithm is applicable to reactions involving a change in mole number. Stoichiometrically balanced reactions are attempted in the forward and reverse directions to achieve chemical equilibrium. The transition probabilities do not depend on the chemical potentials or chemical potential differences of any of the components. We also extend RCMC to work in concert with the isothermal-isobaric ensemble for simulating chemical reactions at constant pressure, and with the Gibbs ensemble for simultaneous calculation of phase and chemical equilibria. Association is treated as a chemical reaction in the RCMC formalism. Results are presented for dimerization of simple model associating fluids. In contrast to previous methods, the reactive Gibbs ensemble can be used to calculate phase equilibrium for associating fluids with very strong bonding sites. RCMC simulations are performed for nitric oxide dimerization and results are compared with available experimental data in the liquid phase. Agreement with experiment is excellent. Results for a vapour phase simulation are also in remarkable agreement with estimates based on second virial coefficient data.