Hybrid functional studies on the optical and electronic properties of graphane and silicane

• Optical and electronic properties of graphane and silicane are studied with the first-principles method.
• Hybrid functional gives a wider valence band and an upward shift of the conduction bands.
• HSE06 functional predicted a more accurate band gap than the PBE one.
• Differences of the dielectric functions between graphane and silicane are noticed.

The optical and electronic properties of graphane and silicane are studied by a first-principles method based on density functional theory, employing both the hybrid (HSE06) and the Perdew–Burke–Ernzerhof (PBE) functionals. Our HSE06 results show that graphane has a direct band gap of 4.49 eV, while silicane has an indirect band gap of 2.94 eV. In graphane, the imaginary part of dielectric function ε2(ω)ε2(ω) has two peaks at 7.70 and 15.03 eV for E||z, while for E||x, there are three peaks lying at 11.56, 13.25 and 14.33 eV. In silicane, ε2(ω)ε2(ω) has a main peak at 8.68 eV for E||z, while there are two peaks at 4.56 and 8.55 eV for E||x. In graphane, the peaks in ε2(ω)ε2(ω) are mainly due to the transitions from C 2p and H 1s states to C 2s and 2p ones; while in silicane, the peaks are primarily originated from the transitions from Si 3p and H 1s states to Si 3s and 3p as well as H 1s states.