First-principles density functional theory for the structural, electronic, and phonon calculations of Ca-doped bilayer graphene.

Density functional theory is adopted for the electronic structure and phonon calculation of Ca-doped bilayer graphene. The AA and AB stacking configurations are simulated, and the atoms are relaxed so that the atomic forces working on them are close to zero (5.0 x 10^-3 eV/°A). In the final relaxation, the symmetry of C8CaC8 is D2h for AA stacking and CS for AB stacking. The formation energy of AA stacking (1.72 eV) is much lower than that of AB stacking (8.07 eV). According to the electronic structure calculations, the Dirac point shifts down from the Fermi level, indicating that the Ca atom behaves as an n-type dopant. The calculated Fermi velocities for pristine bilayer graphene are 7.69x105 (AA stacking) and 7.75 x 10⁵ m/s (AB stacking). Those for Ca-doped bilayer graphene are 7.29 x 10⁵ (AA stacking) and 7.22 x 10⁵ m/s (AB stacking). Phonon calculations revealed that considering the vibrational effect, the defect concentration is 1.4x10¹⁶ cm^-3 in the AA stacking system. Meanwhile, concentration is deficient in the AB stacking system due to the asymmetric defect configuration. [ABSTRACT FROM AUTHOR]