Electronic and optical properties of chair-like and boat-like graphane

We have studied two favorable conformations of graphane, the chair-like graphane and boat-like graphane. In the chair-like, the H atoms attached to the C atoms alternate on both sides of the sheet while in the boat-like, the C bonded H atoms alternate in pair. Both conformations of graphane have a 2D puckered honeycomb like structure with one hydrogen atom bonded covalently ( sp(3)) to each carbon atom. The chair-like belongs to the P (3) over bar m1 (164) space group and the boat-like belongs to the Pmmn (59) space group. We have used the state-of-the-art full potential linear augmented plane wave (FPLAPW) method with different possible approximations for the exchange-correlation (XC) potential. The XC potential was described by the local density approximation (LDA) of Ceperley-Alder (CA), the generalized gradient approximation (GGA) of Perdew-Becke-Ernzerhof (PBE) and the Engel-Vosko generalized gradient approximation (EVGGA). The calculated partial density of states for both configurations, show that there exists a strong hybridization between C and H orbitals which confirms the existence of the covalent bonds. The electronic charge density distribution of both configurations (chair-like and boat-like) has been calculated, the charge accumulates along C-C and C-H bonds. According to the electronegativity values of C (2.55) and H (2.1), it is clear that there is strong covalent bonding between C and H atoms. The linear optical properties give a deep insight into the electronic structure. The calculated values of the energy gap and the bond lengths show good agreement with previous results.