Global optimization of clusters of rigid molecules using the artificial bee colony algorithm.

The global optimization of molecular clusters is an important topic encountered in many fields of chemistry. In our previous work (Phys. Chem. Chem. Phys., 2015, 17, 24173), we successfully applied the recently introduced artificial bee colony (ABC) algorithm to the global optimization of atomic clusters and introduced the corresponding software "ABCluster". In the present work, ABCluster was extended to the optimization of clusters of rigid molecules. Here "rigid" means that all internal degrees of freedom of the constituent molecules are frozen. The algorithm was benchmarked by TIP4P water clusters (H2O)N (N ≤ 20), for which all global minima were successfully located. It was further applied to various clusters of different chemical nature: 10 microhydration clusters, 4 methanol microsolvation clusters, 4 nonpolar clusters and 2 ion-aromatic clusters. In all the cases we obtained results consistent with previous experimental or theoretical studies.