ABINITIO CALCULATION OF CHEMISORPTION SYSTEMS - H ON PD(001) AND PD(110)

We present an ab initio density-functional calculation of the interaction of hydrogen with the Pd(001) and Pd(110) surfaces and with bulk palladium. Our results for the H-Pd system are complemented by calculations for the H-2 molecule, the bulk, and the clean (001) and (110) surfaces of Pd. In the case of H in bulk Pd, we determine the equilibrium geometry and electronic structure and discuss the nature of the Pd-H bond. For the adsorption system H/Pd(001) and H/Pd(110), we determine the preferential adsorption sites, bond lengths, and vibration frequencies of the adsorbate. We relate H-induced softening of Pd-surface-phonon frequencies to a corresponding softening of Pd-Pd interactions in the bulk hydride phase.