First-Principles Electronic-Structure Study for Organic Ferroelectric Tetrathiafulvalene-p-Bromanil

The electronic structure of organic ferroelectric tetrathiafulvalene-p-bromanil (TTF-BA) have been studied by first-principles calculations. It has been found that two antiferromagnetic ordered states, which are assumed to approximate a spin-singlet state, are more stable than the non-magnetic state. Estimated spontaneous polarization values are close to the experimental one. The electronic structure and the evolution of spontaneous polarization are compared with those for nonmagnetic tetrathiafulvalene-p-chloranil (TTF-CA). The relationship among magnetism, orbital hybridization and emergence of spontaneous polarization has been discussed.