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 (${\mathrm{TCNQF}}_4$) are calculated self-consistently from first principles using Car-Parrinello techniques. The calculated electronic charge transfer from the DMQtT molecule to the ${\mathrm{TCNQF}}_4$ 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 ${\mathrm{TCNQF}}_4$ molecule becomes more aromatic. The electronic structure around the Fermi level is characterized by one-dimensional charge transfer states.