Crystal structure and electronic states of tripotassium picene

The crystal structure of potassium-doped picene with an exact stoichiometry (K3C22H14, K(3)picene from here onwards) has been theoretically determined within density functional theory allowing complete variational freedom of the crystal structure parameters and the molecular atomic positions. A modified herringbone lattice is obtained in which potassium atoms are intercalated between two paired picene molecules displaying the two possible orientations in the crystal. Along the c-axis, organic molecules alternate with chains formed by three potassium atoms. The electronic structure of the doped material resembles pristine picene, except that now the bottom of the conduction band is occupied by six electrons coming from the ionized K atoms (six per unit cell). Wavefunctions remain based mainly on picene molecular orbitals getting their dispersion from intralayer edge-to-face CH/pi bonding, while eigenenergies have been modified by the change in the electrostatic potential. The small dispersion along the c-axis is assigned to small H-H overlap. From the calculated electronic density of states, we expect metallic behavior for potassium-doped picene.