Chemisorption of H on Pd(111): An ab initio approach with ultrasoft pseudopotentials

An ab initio study based on local-density-functional (LDF) theory is presented for the chemisorption of hydrogen on the Pd(111) surface. Our calculation uses the Vienna ab initio molecular-dynamics program (VAMP) based on (i) finite-temperature I,DF, (ii) exact calculation of the electronic ground state and Hellmann-Feynman forces after each ionic move, and (iii) ultrasoft pseudopotentials for the electron-ion interaction. Complete geometry optimization for different adsorption sites an carried out. The energetic stability of the adsorption site correlates with the coordination number of the site. The larger the coordination number, the more stable the site. Both geometries and the electronic structure obtained from our theoretical calculations are in good agreement with experimental results.