The structural investigation on small methane clusters described by two different potentials

Structures of molecular clusters have not been well elucidated. In the present study, a fundamental cluster (CH4)n (n ⩽ 40) was theoretically investigated with two potentials; one is a well-known potential called OPLS and the other is a Morse potential obtained from ab initio calculations of the methane dimer. The global minima of methane clusters were searched with the heuristic method combined with geometrical perturbations. The local structure analysis of the global-minimum geometries of the clusters shows that they contain spherical geometries where 12–16 molecules surround a molecule. The structural growth sequences of the OPLS and Morse-potential-based clusters were examined with rotational constants of them and core structures formed by interior molecules. The global-minimum geometries of most of the OPLS clusters with n ⩽ 30 are similar to those of the corresponding Morse-potential-based clusters.