Structural Characterization and Band Electronic Structure of α-(BEDT-TTF)2I3 below its 135 K Phase Transition

Abstract The nature of the 135 K metal-insulator (MI) transition in α-(BEDT-TTF)2l3, abbreviated α-(ET)2l3, was examined by determining the crystal structures above (298 K) and below (120 K) the phase transition and also by calculating the band electronic structures at both temperatures. This study demonstrates that both the crystal and band electronic structures of α-(ET)2l3 change only slightly upon passing through the MI transition. Within each sheetlike network of ET radical cations, the magnitudes of interactions between adjacent pairs of ET molecules (i-j) above and below the MI transition temperature (T MI) were evaluated by calculating their interaction energies, β ij = ⟨Ψ, H off|Ψ⟩, where Ψ1); and Ψ1 are the HOMO's of ET molecules i and j, respectively. The band electronic structures calculated by using single-zeta Slater type orbitals show that α-(ET)2l3 is a semiconductor with band gaps of 13 meV (298 K) and 35 meV (120 K). Thus, within the one-electron model, the apparently metallic properties...