Charge transfer variation caused by symmetry breaking in a mixed-stack organic compound: TTF-2, 5Cl(2)BQ

In the 'neutral-to-ionic' transition presented by some mixed-stack organic compounds, the inter-molecular charge-transfer variation at the critical pr essure or temperature results both from the loss of inversion symmetry and the lattice contraction. We present here a three-dimensional ab initio stud y of the electronic ground state of one of these charge-transfer salts: tet rathiafulvalene-2, 5-dichloro-p-benzoquinone, and discuss the relative impo rtance of the intra- and inter-chain quantum interactions. Within a tight-b inding scheme fitted to the self-consistent results, we show that the weak molecular distortions due to the symmetry-breaking part of the 'neutral-to- ionic' transformation induce a non-negligible contribution to the total cha rge-transfer variation.