  Materials with optimized band gap are needed in many specialized
applications. In this work, we demonstrate that Hellmann-Feynman forces
associated with the gap states can be used to find atomic coordinates with a
desired electronic density of states. Using tight-binding models, we show that
this approach can be used to arrive at electronically designed models of
amorphous silicon and carbon. We provide a simple recipe to include a priori
electronic information in the formation of computer models of materials, and
prove that this information may have profound structural consequences. An
additional example of a graphene nanoribbon is provided to demonstrate the
applicability of this approach to engineer 2-dimensional materials. The models
are validated with plane-wave density functional calculations.
