Organic molecular crystals in electric fields

We present ab initio density functional (DFT) calculations of the electronic properties of organic molecular crystals surfaces in an electric field. We investigate the electronic structure of small slabs of benzene (six layers) and anthracene (four layers) and study their changes due to electric fields perpendicular to the slab surfaces. For extreme fields, charge transfer between the two surfaces could occur in the simulation. We found that benzene and anthracene show a different behavior due to the different electron affinity. While in anthracene two charged layers form at the two surfaces, one of electron type and the other of hole type, electrons from benzene slab are pulled out to vacuum due to negligible or negative electron affinity.