The phase diagram of TTF-TCNQ under pressure

It is shown that the CDW-CDW interaction between TTF and TCNQ chains in TTF-TCNQ has a drastic pressure dependence changing its sign approximately at 5 kbar. This dependence determines the form of the phase transition curves on the T-P plane which turn out to be very similar to those observed experimentally. The recent experiments of Megtert et al. which established the existence of a T-P region where both systems of chains are ordered with a transverse period equal to 2a, may be explained by means of this interchain interaction pressure dependence together with CDW-impurity interaction.