Model of the neutral-ionic phase transformation

A model is presented describing how an organic solid transforms between a neutral and an ionic ground state. Whereas for a one-dimensional stack this transition is expected to be first order, the Coulomb interactions between stacks can cause the phase transition to occur over a broad temperature range by stabilizing an intermediate region in between the neutral and ionic phases, in which both neutral and ionized species coexist, as observed in tetrathiafulvalene-chloranil. © 1981 The American Physical Society.