Title: Structural and bonding character of potassium-doped p-terphenyl superconductors,
Abstract: Recently, there is a series of reports by Wang et al. on the
superconductivity in K-doped p-terphenyl (KxC18H14) with the transition
temperatures range from 7 to 123 Kelvin. Identifying the structural and bonding
character is the key to understand the superconducting phases and the related
properties. Therefore we carried out an extensive study on the crystal
structures with different doping levels and investigate the thermodynamic
stability, structural, electronic, and magnetic properties by the
first-principles calculations. Our calculated structures capture most features
of the experimentally observed X-ray diffraction patterns. The K doping
concentration is constrained to within the range of 2 and 3. The obtained
formation energy indicates that the system at x = 2.5 is more stable. The
strong ionic bonding interaction is found in between K atoms and organic
molecules. The charge transfer accounts for the metallic feature of the doped
materials. For a small amount of charge transferred, the tilting force between
the two successive benzenes drives the system to stabilize at the
antiferromagnetic ground state, while the system exhibits non-magnetic behavior
with increasing charge transfer. The multiformity of band structures near the
Fermi level indicates that the driving force for superconductivity is
complicated.