First-principles study of the electronic and magnetic structure of c(2 x 2) sulfur chemisorbed above Fe(001).

Abstract

We have performed the first, first-principles study of the adsorption of sulfur above a magnetic, Fe surface. Our results, derived from the all-electron, film full-potential linearized augmented-plane-wave method applied to a seven-layer Fe film with and without c(2\ifmmode\times\else\texttimes\fi{}2) layers of S positioned next to the two surface Fe [Fe(S)] layers, include determinations of the equilibrium sulfur height (${H}_{\mathrm{eq}}$) and vibrational frequency, as well as the associated electronic and magnetic structures. We find excellent agreement between our calculated value (1.12 A\r{}) of ${H}_{\mathrm{eq}}$ with the earlier result [1.09(5) A\r{}] derived by Legg, Jona, Jepsen, and Marcus from a dynamical low-energy electron diffraction intensity analysis. The adsorption induces antibonding minority surface states immediately above and below ${E}_{F}$ which play an important role both in reducing the magnetic moment of the Fe(S) atom (by \ensuremath{\sim}20%) and in the rather small calculated increase (0.85 eV) in work function. These states should be clearly resolvable in both integrated and angle-resolved, spin-polarized photoemission and inverse-photoemission experiments. We present additional predictions, including the adsorption-induced changes in the hyperfine fields and in the angle-resolved, spin-polarized surface state spectra, and relate our findings to questions associated with the sulfur-induced poisoning of an iron catalyst.