The atomic structures and electronic properties of potassium-doped phenanthrene from a first-principles study

Abstract

The atomic structures and electronic properties of potassium-doped phenanthrene (PHA) with various doping levels have been investigated using first principles calculations based on van der Waals density functional theory (DFT). Our results show that the possible stoichiometric content of potassium in K_xPHA compounds is x = 1 or x = 2, corresponding to the structural phases K₁-A, K₁-B or K₂-A. The formation energy of the K₂-A phase is −0.32 eV per K atom, which is comparable to the energy of KC₈. These K₃PHA phases, mentioned in previous reports, have a positive formation energy larger than +0.24 eV per K atom, which should not exist in samples. K₂PHA in the K₂-A phase is a metal with three bands crossing the Fermi level, and the Fermi surface sheet along Γ–Z has a cylinder shape associated with the two-dimensional nature of the electronic states. Our calculations suggest that the K₂-A phase is the most stable and reasonable structure in K-doped PHA compounds.