Electronic and spectroscopic properties of the hydrogen-terminated Si(111) surface fromab initiocalculations

We report on a detailed, theoretical study of the electronic and spectroscopic properties of the hydrogen-terminated Si(111) surface. We computed band structures and scanning tunneling microscopy (STM) images, and we analyzed the performance of density-functional theory within the local-density approximation (LDA), and of many-body perturbation theory (at the GW level) in interpreting and rationalizing experimental results. We discuss numerical approximations involved in the implementation of the two theoretical approaches, and the need to control them with extreme care, to reach a robust assessment of the theory. We find that although at the LDA level severe discrepancies with experiment are present, in the description of the surface electronic states, the STM images computed using GW and LDA band structures are qualitatively the same. Computed constant height STM images in close proximity of the surface exhibit bright, round spots on top of H atoms while low-temperature measurements show triangular spots. Our results suggest that to reproduce these triangular shapes, one may need to explicitly consider tip-surface interactions and that the tip-sample distance may as well play a role in determining experimental images. Computed current-voltage characteristics are in qualitative agreement with experiment.