Finding the atomic configuration with a required physical property in multi-atom structures

In many problems in molecular and solid state structures one seeks to determine the energy- minimizing decoration of sites with different atom types. In other problems, one is interested in finding a decoration with a target physical property ( e. g. alloy band gap) within a certain range. In both cases, the sheer size of the configurational space can be horrendous. We present two approaches which identify either the minimum- energy configuration or configurations with a target property for a fixed underlying Bravais lattice. We compare their efficiency at locating the deepest minimum energy configuration of face centered cubic Au - Pd alloy. We show that a global- search genetic- algorithm approach with diversity- enhancing constraints and reciprocal- space mating can efficiently find the global optimum, whereas the local- search virtual- atom approach presented here is more efficient at finding structures with a target property.