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(ethy1enedithio)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 Å, 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.