First principles calculations of surface phonons on Rh(111)

Surface phonons on the high symmetry points of the Rh(111)-surface have been determined using first principles local density functional (LDF) calculations with two different pseudopotentials, once with a planewave and once with a mixed basis-set. Use of the Hellmann-Feynman theorem allowed the calculation of forces and thus the determination of force constants. Due to the lack of experimental or theoretical data for the bulk phonon spectrum, calculations for the bulk properties have also been performed. Both calculations for the bulk phonon spectrum are in excellent agreement with a recently performed experimental study including all observed phonon anomalies. These data do not support the assumption made by Toennies, that the spectrum of a hydrogenated Rh(111) surface would correspond to that of the truncated bulk. The interplanar force constants at the surface have been found to differ rather strongly from the bulk force constants (more than in Pd or Pt, for example), resulting in a very significant influence on the surface phonon frequencies at the zone boundary.