Organic metals. Molecular coordination along the stacking direction of a conducting organic compound: TTF-TCNQ (tetrathiafulvalene- tetracyanoquinodimethane)

Abstract

CNDO/2 molecular orbital calculations have been performed on ionized TCNQ and TTF dimers for different values of relative displacement of the monomers. The intermolecular separation is held fixed. The total energy of the TCNQ dimer goes through two minima, one when the monomers are exactly over each other (eclipsed geometry) and one for which the monomers are slipped with respect to each other (slipped geometry) as observed in TTF-TCNQ. The total energy of the TTF dimer exhibits a minimum for the eclipsed geometry only. The qualitative agreement with previous extended Huckel results highlights the close screening of the core-core interaction by the electrons. The implications of the different geometries with respect to electronic banding of the affinity and ionization levels in segregated stack structures is discussed. © 1979 American Institute of Physics.