Static and dynamical calculations on crystalline TTF-CA

P.LEVY AND H.BONADEO

CHEMICAL PHYSICS

ELSEVIER SCIENCE BV

Lugar: New York; Año: 1990 vol. 144 p. 377 - 381

0301-0104

AbstractStatic and dynamical properties of the neutral phase of the crystalline charge transfer complex tetrathiafulvalene-chloranyl (TTF-CA) are studied in relation to the neutral-ionic phase transition. Intermolecular interactions are represented by an atomatom model (AA) to which charge-charge (QQ) interactions are added. It isfound that upon relaxation of the structure towards minimum energy, no substantial modifications of the unit cell are found when using AA, and that although when QQ is added a noticeable expansion in the direction of the b axis and a contraction in the a axis is observed, there is no tendency of the structure to collapse. Dynamical calculations show that QQ interactions have a negligible effect on calculated vibrational frequencies. It is concluded that the phase transition is not essentially due to electrostatic interactions. Dispersion curves and calculated frequencies at high symmetry points of the Brillouin zone are presented. It is found that the dynamics of the system is essentially three dimensional.