Theory of the Neutral-Ionic Transition in TTF-Chloranil

概要

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A new mechanism of the neutral-ionic transition in TTF-chloranil is presented,through which we derive the temperature-induced. transition as a statisticalmechanically cooperative phenomenon, without supposing the lattice thermal confraction. We take into account the coulomb interaction up to second nearest-neighbors within a chain, the spin degeneracy of the ionic molecular state, as well asthe quantum-mechanical charge transfer. In addition, the inter-chain coulomb interaction is considered in the mean field approximation. The free energy approximately calculated as a function of the degree of ionicity shows that at low temperatures theionic phase becomes lower owing to a large splitting of the spin degeneracy caused bya strong mixing of the neutral and tonic states, whereas at room temperature theneutral phase is lower owing to the electrostatic energy balance.
社団法人日本物理学会の論文
1987-09-15