Polaron Band Structure and Carrier Mobility in Crystals of Diatomic Molecules and Aromatic Hydrocarbons

Abstract

The theory developed in two previous papers is applied to crystals of hydrogen, oxygen, nitrogen, chlorine, iodine, helium, anthracene, naphthalene, and pyrene. The interaction of charge carriers with intramolecular vibrations is calculated and compared with electronic bandwidths. It is shown that the conventional band scheme, wherein electronic and nuclear wavefunctions are assumed separable for the crystal as a whole, is generally inadequate. For most of the systems studied vibronic interactions reduce the quasifree electron and hole bandwidths by a factor of 2 to 10, but in some cases the reduction is so large that the carriers can be considered localized for practical purposes. As a result halogen crystals will behave like p‐type materials, whereas solid helium will be essentially n‐type. The agreement between calculated band structures and measured mobilities in iodine, anthracene, and naphthalene is considerably improved by taking vibronic interactions into account. Without these interactions carrier mean free paths of the order of the lattice spacings are obtained, so that a conventional electronic band calculation produces inconsistent results.