Polymorphism, phonon dynamics and carrier-phonon coupling in pentacene

TL;DR

This study investigates the crystal structure, phonon dynamics, and carrier-phonon interactions in pentacene, revealing two crystalline phases distinguishable by Raman spectroscopy and analyzing their thermodynamic stability and charge transport properties.

Contribution

It provides a detailed computational analysis of pentacene's phases, phonon behavior, and carrier coupling, highlighting differences between phases and their spectroscopic signatures.

Findings

Two crystalline phases of pentacene exist with similar stability.

No temperature-induced phase transition observed.

Carrier-phonon coupling to low-frequency phonons characterized.

Abstract

The crystal structure and phonon dynamics of pentacene is computed with the Quasi Harmonic Lattice Dynamics (QHLD) method, based on atom-atom potential. We show that two crystalline phases of pentacene exist, rather similar in thermodynamic stability and in molecular density. The two phases can be easily distinguished by Raman spectroscopy in the 10-100 cm-1 spectral region. We have not found any temperature induced phase transition, whereas a sluggish phase change to the denser phase is induced by pressure. The bandwidths of the two phases are slightly different. The charge carrier coupling to low-frequency phonons is calculated.