Density functional theory study of alkali doped picene

We employ density functional theory methods to determine the equilibrium structures of $A_x$picene where $A={\rm Na}$, K, Rb, Cs and $x=1,2,3$. We find that alkali doping with one, two and three alkali ions per picene molecule leads to subsequent filling of the LUMO and LUMO+1 derived bands of picene, leading to quarter, half and three quarter filled systems. We analyse the electronic structures using tight binding methods to derive the kinetic energy part of the underlying Hubbard Hamiltonian. As the interaction strength $U$ on the picene molecules is expected to be large compared to the band width, we also employ manybody methods on the resulting Hamiltonian. We compare our results to photoemission experiments.