The role of electron-phonon coupling on optoelectronic properties of crystalline naphthalene from first principles*

Organic molecular crystals, periodic arrays of non-covalently bound molecules held together by electrostatic and dispersion forces, are chemically diverse platforms for fundamental studies and use in optoelectronic applications. Using density functional perturbation theory, we compute the finite-temperature electronic structure of naphthalene, a prototypical molecular crystal. Due to electron-phonon interactions, the direct gap decreases by 0.2 eV at room temperature. We also compute the corresponding broadening and lifetimes of single-particle excitations relevant to transport properties. To account for the dispersive forces that play a large role in these systems, we use van der Waals density functionals to calculate the crystal structure and phonon dispersion. We compare our calculations to experiments and discuss the consequences on optoelectronic properties of naphthalene and other organic crystals.