This proposal is a low-cost/high-gain first step in an ambitious project: namely, to develop a combined neutron scattering and electronic structure calculation approach as a means of understanding and exploiting the relationship between local structure and electronic structure in functional materials. We will measure total neutron scattering data for two compounds ¿ a-Si and superconducting YBa2Cu3O6.9 ¿ and use these data in two ways. First, to develop an electronic structure + RMC refinement strategy that will enable the generation of experimentally-driven atomistic configurations simultaneously consistent with diffraction and with known features of the electronic structure. And, second, to perform large-scale electronic structure calculations on RMC models of key crystalline materials to determine how the electronic structure is affected by including two-body structural correlations.