Computational method for angle-resolved photoemission spectra from repeated-slab band structure calculations

A versatile method for angle-resolved photoemission spectra (ARPES) calculations is reported within the one-step model of photoemission. The initial states are obtained from a repeated-slab calculation using the projector-augmented wave (PAW) method. ARPES final states are constructed by matching the repeated-slab eigenstates of positive energy with free electron states that satisfy the time-reversed low-energy electron diffraction boundary conditions. Nonphysical solutions of the matching equations, which do not respect the flux conservation, are discarded. The method is applied to surface-normal photoemission from graphene as a function of photon energy from threshold up to 100 eV. The results are compared with independently performed multiple scattering calculations and very good agreement is obtained, provided that the photoemission matrix elements are computed with all-electron waves reconstructed from the PAW pseudowaves. However, if the pseudowaves are used directly, the relative intensity between $\ensuremath{\sigma}$- and $\ensuremath{\pi}$-band emission is wrong by an order of magnitude. The graphene ARPES intensity has a strong photon energy dependence including resonances. The normal emission spectrum from the $\ensuremath{\pi}$ band shows a hitherto unreported sharp resonance at a photon energy of 31 eV. The resonance is due to a two-dimensional interband transition and highlights the importance of matrix element effects beyond the final-state plane-wave approximation.