Colloidal clusters from a global optimization perspective

Abstract

Modern microscopy techniques opened new perspectives to look at colloidal clusters. It is now possible to visualize the colloidal particles forming the cluster, which provides relevant experimental data that can be combined with detailed information resulting from structural optimization to understand phenomena at the mesoscale. From the theoretical view point, short-ranged Morse pair potentials have been successfully applied to model interactions between colloidal particles, while the development of efficient global optimization methods has allowed one to face the difficult task of searching for the geometry of the cluster that minimizes energy. In this work, we have carried out a thorough review concerning the global optimization methods proposed in the literature. The optimization of the title systems relies on the methods especially designed to deal with atomic clusters. Studies involving the global optimization of colloidal clusters were also surveyed.We employ the evolutionary algorithm developed in our group to search low-energy structures of colloidal clusters that are modeled with short-ranged Morse potentials. To the best of our knowledge, this is the first time that such kind of global optimization algorithms are applied to colloidal clusters. The method shows to be efficient for discovering the putative global minima in the cluster size-range N≤38. The results appear to indicate that, for colloidal clusters, significant structural changes due to the variation in the range of the interaction are unlikely to occur. Also the quasi-degeneracy of both global and local minima, that is usually present in these aggregates, is not raised up by modifying the composition of the cluster or decreasing the range of the interaction between the colloidal particles. In contrast, charged particles have shown a great influence on the stable structure of the clusters.