title: Ba2phenanthrene is the main component in the Ba-doped phenanthrene superconductor.
abstract: We have systematically investigated the crystal structure of Ba-doped phenanthrene with various Ba doping levels by the first-principles calculations combined with the X-ray diffraction (XRD) spectra simulations. Although the experimental stoichiometry ratio of Ba atom and phenanthrene molecule is 1.5:1, the simulated XRD spectra, space group symmetry and optimized lattice parameters of Ba1.5phenanthrene are not consistent with the experimental ones, while the results for Ba2phenanthrene are in good agreement with the measurements. The strength difference of a few XRD peaks can be explained by the existence of pristine phenanthrene. Our findings suggest that instead of uniform Ba1.5phenanthrene, there coexist Ba2phenanthrene and undoped phenanthrene in the superconducting sample. The electronic calculations indicate that Ba2phenanthrene is a semiconductor with a small energy gap less than 0.05 eV.
authors.affiliation: Beijing Computational Science Research Center, Beijing 100084, China.
authors.forename: Xun-Wang
authors.initials: XW
authors.lastname: Yan
authors.affiliation: Beijing Computational Science Research Center, Beijing 100084, China.
authors.forename: Zhongbing
authors.initials: Z
authors.lastname: Huang
authors.affiliation: Beijing Computational Science Research Center, Beijing 100084, China.
authors.forename: Hai-Qing
authors.initials: HQ
authors.lastname: Lin