Electronic structure of7,7,8,8−tetracyano−p−quinodimethane(TCNQ)

Abstract

The electronic structure of $7,7,8,8-\mathrm{tetracyano}-p-\mathrm{quinodimethane}$(TCNQ) is calculated using a complete neglect of differential overlap (CNDO) parametrization similar to that recently introduced by Lipari and Duke for aromatic molecules. Comparison with various other theoretical methods is presented and it is shown that the present CNDO parametrization gives the best agreement with ab initio (i.e., Hartree-Fock) calculations. New ultraviolet photoemission data for solid TCNQ are presented and shown to be in good agreement with the gas-phase spectrum, in contrast to the results of others. The polarization energy of TCNQ is found to be 1.08 eV. The present CNDO parametrization gives excellent agreement with gas phase, and our solid-phase ultraviolet photoemission measurements. Furthermore, the optical spectrum is calculated and shown to be in agreement with the observed inelastic electron scattering data in the prediction of both the dipole-allowed transitions and the monopole-allowed transitions.