Abstract
We develop a variational approach to an extended Holstein model, comprising both local and nonlocal electron-phonon coupling. The approach is based on the minimization of a Bogoliubov bound to the Helmholtz free energy. The ambivalent character of nonlocal coupling, which both promotes and hinders transport, is clearly observed. Furthermore, a salient feature of our results is that the local and nonlocal couplings can compensate each other, leading to a reduction of polaronic effects and a quasi-free character of the excitation. Our findings have implications for organic crystals of -conjugated molecules, where this electron-phonon coupling mechanism plays an important role.
- Received 10 July 2003
DOI:https://doi.org/10.1103/PhysRevB.69.144302
©2004 American Physical Society