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A Monte Carlo Study of Isomers and Structural Evolution in Benzene−Cyclohexane Clusters:  (C6H6)(C6H12)n, n = 3−7, 12

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journal contribution
posted on 20.12.2007, 00:00 by David C. Easter, Jessica A. Roof, Laura Jeanne Butts
Monte Carlo simulated annealing strategies, carried out on four different potential energy surfaces, are applied to benzene−cyclohexane clusters, BCn, n = 3−7, 12, to identify low-energy isomers and to trace the evolution of structures as a function of cluster size. Initial structures are first heated to ensure randomization, and subsequent annealing yields optimized rigid, low-energy clusters. Five major structural isomers are identified for BC3:  one assumes the form of a symmetric, modified sandwich; the remaining four lack general symmetry, assuming distorted tetrahedral arrangements. For BC4 and larger clusters, the number of low-temperature isomers is large. It is, nevertheless, feasible to classify isomers into groups based on structural similarities. The evolution of BCn structures as a function of cluster size is observed to follow one of two primary paths:  The first maximizes benzene−cyclohexane interactions and places benzene in or near the BCn cluster center; the competing path maximizes cyclohexane−cyclohexane interactions and distances benzene from the cluster's center of mass. Results for BC3 and BC4 are discussed with reference to experimental results and models previously applied to interpret benzene−argon cluster spectra.