Clusters, columns, and lamellae - minimum energy configurations in core softened potentials

We give evidence that particles interacting via the simple, radially symmetric square-shoulder potential can self-organize in highly complex, low-symmetry lattices, forming thereby clusters, columns, or lamellae; only at high pressure compact, high-symmetry structures are observed. Our search for these ordered equilibrium structures is based on ideas of genetic algorithms, a strategy that is characterized by a high success rate. A simple mean-field type consideration complements these findings and locates in a semi-quantitative way the cross-over between the competing structures.