Surface structure of Rh(001) and p (1 x 1) H on Rh(001): An unresolved discrepancy between experiment and theory

Low-energy-electron diffraction intensity measurements and analysis are used to obtain multilayer surface relaxation of clean and hydrogen-saturated Rh(001). Results averaged over three data sets show the first interlayer spacing of clean Rh(001) to be expanded (+1.0%+/-0.6%) relative to the bulk spacing (1.902 Angstrom) and the second interlayer spacing to be contracted (-0.7%+/-0.5%). Chemisorbed hydrogen atoms are found to reside at fourfold hollow sites 0.88+/-0.05 Angstrom above the 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 between calculated and measured multilayer relaxation of Rh(001). [S0163-1829(98)04407-5].