A theoretical study of neutral and reduced tetracyano-p-quinodimethane (TCNQ)

The molecular structure of neutral, anionic, and dianionic tetracyano-p-quinodimethane (TCNQ), as well as the electron affinity of TCNQ, have been studied with HF, MP2, and different density functional theory (DFT) procedures. The optimized geometries compare well with the available experimental data, although the Cequivalent toN bond distance is not correctly described at the MP2 level. The calculated parameters are rather insensitive to the basis set employed, and the addition of diffuse functions does not yield significant changes. When the extra electrons are added, the central ring of TCNQ progressively becomes more aromatic. Compared with the CCSD(T) estimate, the value of the adiabatic electron affinity is overestimated at the DFT level. The B3P86 functional leads to the largest deviations, higher than 1 eV, whereas the BLYP functional affords the best results. At the MP2 level, the value obtained after projection of the major spin contaminating component (PMP2) is in good agreement with the CCSD(T) result. Single-point PMP2 calculations over DFT-optimized geometries are suggested as a low-cost alternative strategy to study more extended systems. (C) 2004 Elsevier B.V. All rights reserved.