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
metals with small hole and electron pockets. If the oxidation state of M' is +3, M'Nb2Se4 phases are calculated to be one-dimensional metals. Therefore, it would be interesting to measure the resistivity anisotropy as well as the possible superlattice modulation of these compounds.Acknowledgment. This work was supported by NATO, Scientific Affairs Division, and also by DOE, Office of Basic Sciences, Division of Materials Science, under Grant DE-FG05-86ER45259. We are thankful to Dr. A. Meerschaut for references and valuable comments.
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