The prototype compound for the neutral-ionic phase transition, namely TTF-CA, is theoretically investigated by first-principles density functional theory calculations. The study is based on three neutron diffraction structures collected at 40, 90 and 300 K (Le Cointe et al., Phys. Rev. B 51, 3374 (1995)). By means of a topological analysis of the total charge densities, we provide a very precise picture of intra and inter-chain interactions. Moreover, our calculations reveal that the thermal lattice contraction reduces the indirect band gap of this organic semi-conductor in the neutral phase, and nearly closes it in the vicinity of the transition temperature. A possible mechanism of the neutral-ionic phase transition is discussed. The charge transfer from TTF to CA is also derived by using three different technics.
@article{arxiv.cond-mat/0210017,
title = {Neutral-ionic phase transition : a thorough ab-initio study of TTF-CA},
author = {V. Oison and C. Katan and P. Rabiller and M. Souhassou and C. Koenig},
journal= {arXiv preprint arXiv:cond-mat/0210017},
year = {2009}
}