Anomalous multilayer relaxation of Pd{001}

A low-energy electron-diffraction intensity analysis of a clean Pd{001} surface finds the first interlayer spacing expanded by about 3% and the second interlayer spacing slightly contracted by about 1% with respect to the bulk value (1.945). These results contradict the trend usually observed or theoretically predicted on fcc {001} surfaces, where the first relaxation is a compression and the second is an expansion. Possible origins of this behavior are suggested. © 1990 The American Physical Society.