Nonlocal electron-phonon coupling in the pentacene crystal: beyond the Γ-point approximation

Area of Science:

• Organic molecular semiconductors
• Condensed matter physics
• Charge transport phenomena

Background:

• Increasing interest in nonlocal (Peierls-type) electron-phonon mechanisms for organic semiconductor charge transport.
• Literature predominantly relies on Γ-point phonon modes for estimating nonlocal coupling constants.

Purpose of the Study:

• Investigate the influence of phonon dispersion across the entire Brillouin zone on nonlocal electron-phonon couplings.
• Provide a more accurate assessment of coupling constants in pentacene crystals.

Main Methods:

• Utilized a supercell approach to obtain phonon modes.
• Analyzed phonon modes spanning the entire Brillouin zone, not just the Γ point.
• Calculated variance of transfer integrals at room temperature.

Main Results:

• Nonlocal couplings are substantially underestimated when only considering Γ-point phonons.
• Transfer integral variance underestimated by up to 40% for herringbone dimers and over 80% for cofacial dimers.
• Nonlocal coupling is slightly larger for holes than electrons.

Conclusions:

• Phonon dispersion significantly impacts nonlocal electron-phonon couplings in pentacene.
• Γ-point approximations lead to considerable underestimation of charge transport properties.
• Accurate modeling requires treating acoustic and optical phonon interactions on equal footing.