A HEURISTIC MOLECULAR-DYNAMICS APPROACH FOR THE PREDICTION OF A MOLECULAR-CRYSTAL STRUCTURE

A general method has been developed to predict the structures of molecular crystals without any constraints on the space symmetry nor on the lattice constants. A constant-pressure molecular dynamics (MD) technique, treating the lattice constants as variables, is employed in the search of candidate structures (''shaking'' process). A heuristic MD search is proposed to reduce redundant sampling in the shaking process. The structures of the thus sampled species are further optimized in geometry by the steepest descent method (''quenching'' process). This general method was coded in a program named MDCP (Molecular Dynamics for Crystal Packing), and was applied to the prediction of the crystal structures of CO2, benzene, and pyrimidine molecules, as test examples. For CO2 and benzene crystals, the experimentally observed structures were well reproduced through our method. For pyrimidine, however, a slight difficulty was observed under the atom-atom potentials employed here, although near-miss structures were frequently encountered.