Fundamental Gap of Fluorographene by Many-Body GW and Diffusion Quantum Monte Carlo Methods*

Fluorographene (FG) is a promising large band gap graphene-derivative. Predictions of its fundamental gap (Δ) vs experiments vary rather significantly. We present benchmark Δ for FG from large-scale many-body GW and fixed-node diffusion Monte Carlo (FNDMC) computations. Both approaches arrive at Δ≈7.1±0.1 eV. Second part presents a possibility to compute Δ from neutral energy differences within 1-determinant Bloch-orbital-based FNDMC. We argue, why instead of the expected optical gap, such an approach results in energy differences that do not account for an electron-hole interaction and nominally correspond to Δ in the thermodynamic limit. Conditions when this case actually applies are outlined as well.