Reserving discrepancies between LEED and STM through ab initio calculations: Surface and bonding of sulfur on Mo(110)

The adsorption of sulfur at 0.5 ML in both c(2 x 2) and [(2)((2) over bar)( 1)(1)] configurations on the Mo(110) surface is studied using the density-f unctional, pseudopotential method with a plane-wave basis and a seven-layer slab geometry in conjunction with scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED) experiments. The sulfur adatoms are placed in different possible binding sites in order to determine the most f avorable adsorption site. The [(2)((2) over bar)(1)(1)] overlayer is more s table than the c(2 x 2) by 0.31 eV, in agreement with experiment. The great er stability of the [(2)((2) over bar)(1)(1)] structure is attributed to di fferences in metal-metal bonding. Sulfur is predicted to adsorb at a low-sy mmetry position near the long-bridge site; the long-bridge site is slightly less favorable in energy. Simulated STM images of the sulfur-covered surfa ce are constructed, and found to model well the experimental images. We fin d that the bright areas in the calculated STM images do not necessarily cor respond to the position of the sulfur atoms, which explains the difference between the LEED pattern and the experimentally observed STM images. [S0163 -1829(99)02340-1].