On the band electronic structure of X [M (dmit)2]2 (X = TTF, (CH3)4N ; M = Ni, Pd) molecular conductors and superconductors

Abstract

The tight binding band electronic structures of the molecular conductors X[M(dmit)2]2 (X = TTF, (CH3)4N ; M = Ni, Pd) are reported. In the cases of TTF(Ni(dmit)2] 2, α- and α'-TTF [Pd(dmit)2]2, it is shown that both the LUMO (lowest unoccupied molecular orbital) and HOMO (highest occupied molecular orbital) bands of the acceptor are partially filled. Our calculations show that these phases are quasi-1D metals. The wave vectors of the experimentally observed CDW (charge density wave) instabilities are discussed on the basis of these results. The crucial role of dimerization within the acceptor stacks is emphasized. In dimerized systems like (CH 3)4N[Ni(dmit)2]2 and δ-TTF[Pd(dmit) 2]2 only one band of the acceptor is partially filled according to our calculations. It is suggested that the metal-semiconductor transition at 120 K of the latter phase could be due to nesting of the Fermi surface.