Theoretical study of the charge transfer in the organic crystal of dimethylquaterthiophene and tetrafluoro-tetracyanoquinodimethane

The electronic and geometrical structures of the organic charge-transfer crystal of dimethylquaterthiophene (DMQtT) and tetrafluorotetracyanoquinodimethane (TCNQF(4)) are calculated self-consistently from first principles using Car-Parrinello techniques. The calculated electronic charge transfer from the DMQtT molecule to the TCNQF(4) molecule is 0.46e +/- 0.05e. This charge transfer is accompanied by a structural change in which the DMQtT molecule adopts a more quinoid geometry (compared to the aromatic structure of the neutral DMQtT molecule) and the TCNQF(4) molecule becomes more aromatic. The electronic structure around the Fermi level is characterized by one-dimensional charge transfer states.