Ab-initio and semiempirical electronic structural studies on bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET)

We report electronic structure calculations for the organic molecule bis(ethylenedithio)tetrathiafulvalene (BEDT-TTF or ET), associated with the highest T_c 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 A and 1° 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.