Modelling of XPS of hydrosilylated graphene

For the modelling of XPS, we chose a 7 × 7 × 1 graphene supercell with Et₃SiH attached onto it, dissociated into a triethylsilyl group and an H atom bonded to opposite sides of the graphene sheet. We have used plane-wave based DFT code VASP⁶⁶ to optimize the structure. The PBE⁶⁷ exchange-correlation potential has been used within generalized gradient approximation. The structures were optimized using the conjugate gradient method with forces calculated from the Hellman–Feynman theorem. The energy and the Hellman–Feynman force thresholds are kept at 10⁻⁵ eV and 10⁻² eV Å⁻¹, respectively. For geometry optimization, a 5 × 5 × 1 Monkhorst–Pack k grid is used. This optimized structure was used to calculate XPS with the DFT using the PAW⁵⁴-based GPAW⁵⁵ code. To compute the binding energy measured by XPS, we computed the total energy difference between the ground state and the Si2p core-ionized state.