Electrostatic interactions in tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ): Madelung energy and near-neighbor interactions

Abstract

The Madelung energy of tetrathiafulvalenium-tetracyanoquinodimethanide (TTF-TCNQ) has been calculated as a function of assumed charge transfer, charge distribution, and temperature, using a modified Evjen summing criterion. A large, temperature-independent, Madelung energy, EM --2.3 eV/molecule (--53 kcal/mole), was calculated for the case of delocalized unit charges on the molecules. EM alone is shown to be insufficient to stabilize charge transfer in TTF-TCNQ, and the polarization energy is shown to be the most plausible source of additional energy gain upon charge transfer. The near-neighbor Coulomb interactions are evaluated and shown to be the major source of energy gain upon charge delocalization on the molecule.

Collective mode dispersions of organic chain compounds

“…The lower orbitals participate in the intraband and interband transitions due to partial filling of corresponding bands. Extensive calculations of the stability of TTF-TCNQ show that it is not Madelung energy but dispersive forces, accounted by such orbitals, that stabilize this crystal [11][12][13][14]. Thus, motivated by the above questions, in this paper we investigate collective excitations within the model of a quasione-dimensional conductor, proposed in Ref.…”

The atom–atom approximation and the lattice energies of 2,2'-bis-1,3-dithiole (TTF), 7,7,8,8-tetracyanoquinodimethane (TCNQ) and their 1:1 complex (TTF–TCNQ)

“…HC ~s(( Metzger & Bloch (1975), first column, Table 4; (b) Epstein et al (1976), set 1, Table 3; (c) Epstein et al (1976), set 2, Table 3; (d) Epstein et al (1976), set 3, Table 3. * The numbering of atoms is as given in Fig.…”

“…2. Rcfcrences: (a) Metzger & Bioch (1975), Qm, Table 5; (b) Metzger & Bloch (1975), Qn, Table 5; (c) Metzger & Bloch (1975), fourth column, Tablc 5; (d) Epstein et al (1976), set 1, Table 2; (e) Epstein et aL (1976), set 2, Table 2. * The numbering of atoms is as given in Fig.…”

“…Interest in the calculation of the lattice energies of organic donor-acceptor crystals with high electrical conductivity is growing (Metzger & Block, 1975;Epstein, Lipari, Sandman & Nielsen, 1976;Klimenko, Krivnov, Ovchinnikov, Ukrainskii & Shvets, 1976;Scott, La Placa, Torrance, Silverman & Welber, 1977;. In addition, enthalpies of formation and sublimation have been determined experimentally (Metzger, 1977).…”

“…Among these are the classical electrostatic (Madelung) energy, the van der Waals energy, the core repulsion energy, the exchange energy caused by intermolecular electron wave-function overlap along chains, the configuration interaction energy and the energy of delocalization of electrons and holes in bands. The electrostatic energy is the only one which could be calculated rather easily by the Ewald or Evjen method (Epstein et al, 1976). The other contributions demand extensive quantum-mechanical calculations, which still have to be developed (Smit, 1978;Andr~ & Ladik, 1975;Rae, 1969).…”