Structural ground state exploration of Lennard-Jones-Gauss clusters from genetic algorithms.

Generally, structures described by pair potentials tend to be compact and isotropic, as in the case of the Lennard-Jones potential. However, introducing a term that produces competing length scales within the interatomic potential can lead to structures with alternative characteristics. This paper searches for and analyzes the low-energy structures for the Lennard-Jones-Gauss double well potential, a classical force-field that is relatively accurate for transition metals. In some areas of the explored parameter space, we find compact atomic structures similar to those found in the Lennard-Jones potential, however we also find regions where the low energy structure is caged or possesses a nontrivial, anisotropic point symmetry group. Metallic clusters with these characteristics possess good catalytic and optical properties, and could also be used to form quasicrystals. We explore the parameter phase space for the lowest energy structures for atomic clusters with 20 to 70 atoms within a selected range of the two parameters describing the potential. We also report some results with a finer parameter grid exploration for the region in which more diverse structures are found. For this, we report results for sizes of structures between 20 to 50 atoms. Cluster stability is also explored by investigating the appearance of imaginary vibrational modes on the low energy configurations, which can give information on if the structure can realistically exist. Parameter regions where caged structures correspond to the lowest energy configurations can be of great interest for materials and supra-chemistry design.