Ab initio study of the (2 x 2) phase of barium on graphene

We present a first-principles density functional theory study on the structural, electronic and dynamical properties of a novel barium doped graphene phase. Low energy electron diffraction of barium doped graphene presents clear evidence of (2 x 2) spots induced by barium adatoms with BaC8 stoichiometry. First principles calculations reveals that the phase is thermodynamically stable but unstable to segregation towards the competitive BaC6 monolayer phase. The calculation of phonon spectrum confirms the dynamical stability of the BaC8 phase indicating its metastability, probably stabilized by doping and strain conditions due to the substrate. Barium induces a relevant doping of the graphene pi states and new barium-derived hole Fermi surface at the M-point of the (2 x 2) Brillouin zone. In view of possible superconducting phase induced by foreign dopants in graphene, we studied the electron-phonon coupling of this novel (2 x 2) obtaining lambda = 0.26, which excludes the stabilization of a superconducting phase.