SURFACE-STRUCTURE OF RH(001) AND P(1X1)H ON RH(001) - AN UNRESOLVED DISCREPANCY BETWEEN EXPERIMENT AND THEORY

Low-energy-electron diffraction intensity measurements and analysis ar e used to obtain multilayer surface relaxation of clean and hydrogen-s aturated Rh(001). Results averaged over three data sets show the first interlayer spacing of clean Rh(001) to be expanded (+1.0%+/-0.6%) rel ative to the bulk spacing (1.902 Angstrom) and the second interlayer s pacing to be contracted (-0.7%+/-0.5%). Chemisorbed hydrogen atoms are found to reside at fourfold hollow sites 0.88+/-0.05 Angstrom above t he Rh(001) surface, and to modify significantly the first (+4.1+/-1.0% ) and second (-2.2%+/-1.0%) interlayer spacing relative to bulk values . These results confirm the existence of systematic differences betwee n calculated and measured multilayer relaxation of Rh(001). [S0163-182 9(98)04407-5].