Global minimum geometries of acetylene clusters (HCCH)n with n < or = 55 obtained by a heuristic method combined with geometrical perturbations.

Geometry optimization of acetylene clusters (HCCH)(n) in the range of n < or = 55 was carried out with a recently proposed intermolecular potential consisting of Morse potentials, damped dispersion terms, and damped Coulomb terms. The heuristic method developed by the present author was used in the optimization: optimal geometries were searched by using geometry perturbations and subsequent local optimizations. The calculations were repeated until the global minimum was found for each cluster at least three times. The obtained results were analyzed to examine structural evolution of the clusters. The geometries of the clusters with n > or = 25 were similar to the geometry in the cubic crystal of acetylene whereas smaller clusters take icosahedron-based geometries.