Orientational Peierls Transition in Quasi One-Dimensional Organic Solids

Abstract

A simple model of a stack of planar molecular ions is considered in tight-binding approximation. I show that the modulation of the transfer integral of the extended $\pi$-electron wave functions of two adjacent molecular ions by a rotational degree of freedom and the softening of the corresponding zone boundary libron $q_L=\pm \frac{\pi }{z_0}$ leads to an orientational Peierls transition. The possible relevance to the metal-insulator transition in tetrathiafulvalene tetracyanoquinodimethane is stressed.