Magnetism and Charge ordering in TMTTF$_2$-PF$_6$ organic crystals
  Using a combination of Density Functional Theory, mean-field analysis and exact diagonalization calculations we reveal the emergence of a dimerized charge ordered state in TMTTF$_2$-PF$_6$ organic crystal. The interplay between charge and spin order leads to a rich phase diagram. Coexistence of charge ordering with a structural dimerization results in a ferroelectric phase, which has been observed experimentally. The tendency to the dimerization is magnetically driven revealing TMTTF$_2$-PF$_6$ as a multiferroic material. 
Gianluca Giovannetti, Sanjeev Kumar, Jean-Paul Pouget, Massimo Capone
cond-mat.str-el cond-mat.mtrl-sci