Role of Interchain Interactions in the Neutral-Ionic Phase Transition

In this paper, the role of short-range interchain interactions in the temperature-induced neutral-ionic or valence instability of four charge transfer (CT) crystals (4,4′-dimethyltetrathiafulvalene-chloranil, tetrathiafulvalene-chloranil, tetrathiafulvalene-fluoranil, and tetramethylbenzidine-tetracyanoquinodimethane) is analyzed through a topological analysis of the intermolecular electronic density. Comparing the variation in interchain interactions at the phase transition with the corresponding change of the Madelung energy and of the dimerization energy offers clues about the driving force and the mechanism of the neutral-ionic transition in the considered CT crystals.