The inverse hand-structure problem of finding an atomic configuration withgiven electronic properties

Modern crystal-growth techniques, such as molecular beam epitaxy or metal-o rganic chemical-vapour deposition, are capable of producing prescribed crys tal structures, sometimes even in defiance of equilibrium, bulk thermodynam ics. These techniques open up the possibility of exploring different atomic arrangements in search of a configuration that possesses given electronic and optical properties'. Unfortunately, the number of possible combinations is so vast, and the electronic properties are so sensitive to the details of the crystal structure, that simple trial-and-error methods (such as thos e used in combinatorial synthesis(2)) are unlikely to be successful. Here w e describe a theoretical method that addresses the problem of finding the a tomic configuration of a complex, multi-component system having a target el ectronic-structure property. As an example, we predict that the configurati on of an Al0.25Ga0.75As alloy having the largest Optical bandgap is a (GaAs )(2)(AlAs)(1)(GaAs)(4)(AlAs)(1) superlattice oriented in the [201] directio n.