DFT study of honeycomb Sb layers on the Ag(111) surface

Abstract

The electronic structure of the Sb layer on Ag(111), recently reported to have a flat (√3 × √3) honeycomb structure similar to that of graphene [Y. Shao et al., Nano Lett. (2018) 18:2133–9], is studied by means of relativistic DFT calculations. In accordance with earlier results, a flat free Sb monolayer is found to be metastable, as follows from the existence of an imaginary phonon mode. The layer spontaneously reconstructs into a buckled honeycomb structure, which leads to the metal-to-nonmetal transition. It is suggested therefore that the formation of a flat Sb honeycomb layer becomes possible just because of the substrate-induced tensile strain, which results in the stabilization of the structure. The binding (adsorption) energy per Sb atom for the honeycomb structure is found to be rather strong, 4.61 eV, which can be explained by a significant lateral attraction between Sb adatoms. The formation of the honeycomb structure and its stability are studied by performed Monte Carlo simulations within the lattice-gas model either with account for trio interactions, or with some effective energy parameters. The SOC only slightly changes the band structure of the system, but, due to pronounced downward shift of the cone-like band in vicinity of K point, leads to the second surface band crossing EF. A detailed analysis of the localization of the wave functions indicates that the bands crossing EF loose the surface weight away from K point, so that they are not localized in the Sb adlayer in the net Brillouin zone.