We report electronic structure calculations for the organic molecule bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET), associated with the highest T, organic superconductors. The experimental structures exhibit considerable disorder in the outer rings and concomitant uncertainty in the structures. We find that Hartree-Fock (6-31G** basis set) calculations leads to results within 0.01 Angstrom and 1 degrees of experiment for the ordered regions allowing us to predict structures for the disordered regions expected to have this accuracy. We report optimized geometries and atomic charges for ET, ET(+), and ET(+1/2) that should be useful for atomistic simulations.