This computational experiment introduces undergraduate chemistry students to one of the areas of active research, study of gas-phase molecular clusters. Since students are familiar with the molecular mechanics method using PCMODEL from previous courses, it is used, in this experiment, to determine the minimum energy structures and binding energies of water-methanol and water-water clusters. Some of the cluster properties are known to exhibit a non-uniform dependence on cluster size, termed as "magic number" effects. The binding energy differences between successive clusters is known to be one such property and is used in this study to identify magic number clusters. The results obtained in this study using PCMODEL are compared with experimental results on methanol-water clusters, and with previous theoretical calculations on water clusters, which used an intermolecular potential based on ab initio calculations. The present results are in good agreement with these previous calculations thereby showing that the molecular mechanics force field is well parametrized for this system.
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Citation
Kahn, D.; Viswanathan, R. J. Chem. Educ.1997 74 982.
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