Antiferromagnetism in Potassium-Doped Polycyclic Aromatic Hydrocarbons

First-principles density functional calculations are performed to investigate the magnetic characteristics in K-doped polycyclic aromatic hydrocarbons (PAHs) including phenanthrene, picene, 1,2:5,6-dibenzanthracene, 7-phenacene, and 1,2;8,9-dibenzopentacene. With the help of lowest energy crystal structures, the calculated total energies indicate that all five K-doped PAHs are stabilized in an antiferromagnetic ground state, with antiparallel spins between two molecular layers. The magnetic moment in these K-doped PAHs is increased with the increase of benzene rings number, while it is not sensitive to the arrangement of benzene rings. The enhancement of the magnetic moment is caused by a stronger spin splitting near the Fermi level and an increase of magnetic C atoms induced by K atoms with the increase of molecular size. Our results also indicate that the magnetism strongly depends on the crystal structure.