Electronic properties of oligoacenes from first principles

We present the electronic band structures and dielectric tensors for a series of crystalline linear oligoacenes—i.e., naphthalene, anthracene, tetracene, and pentacene—calculated within the density functional framework. The band dispersions, the effective charge carrier masses, and the optical response are discussed as a function of the oligomer length compared to previously reported calculations. The total band dispersions of the two topmost valence and lowest conduction bands are between 0.14 and $0.52\mathrm{eV}$, which, however, are strongly anisotropic. Regarding the charge transport properties, the band dispersions are large enough for bandlike transport only along crystalline directions within the herringbone plane. Except for naphthalene, the conduction bands are more dispersive than the valence bands. This indicates that the electron transport is favored compared to hole migration. The revised stable pentacene single-crystal structure exhibits the largest conduction-band dispersions among the series. Consequently the effective electron masses in pentacene are only $0.8m_0$, whereas the hole masses are in the order of $1.3m_0$. The electronic and optical gaps and thus the onset of the optical response decrease almost linearly, when going from naphthalene to pentacene.