We systematically investigate the crystal structure of Ba-doped phenanthrenewith various Ba doping levels by the first principle calculation methodcombining with the X-ray diffraction (XRD) spectra simulation. The optimizedlattice parameters and the simulated XRD spectra of Ba$_2$phenanthrene are ingood agreement with the experiment ones, and the strength difference of a fewof XRD peaks can be explained by the existence of undoped phenanthrene in theexperimental sample. Although the stoichiometry ratio of Ba atom andphenanthrene molecule is 1.5:1, the simulated XRD spectra, space group symmetryand the optimized lattice parameters of Ba$_{1.5}$phenanthrene are notconsistent to the measured values. The sample of Ba-doped phenanthrene isdeduced to be the mixture of Ba$_2$phenanthrene and some amount of undopedphenanthrene, instead of uniform Ba$1.5$phenanthrene. Our calculations indicatethat Ba$_2$phenanthrene is a semiconductor with a small energy gap less than0.05 eV. Our findings provide the fundamental information of crystal structureand electronic properties of Ba-doped phenanthrene superconductor.
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