Hydrogen adsorption on Ru(001) surface from density-functional periodic calculations

A systematic investigation of hydrogen on Ru(0 0 1) surface has been carried out by means of periodic DFT calculations. The calculated vibrational frequencies of 1109 and 785 cm(-1) for H adsorbed in (root 3 x root 3)R30 degrees and 1173 and 905 cm(-1) for H adsorbed in (1 x 1) pattern were attributed to perpendicular and doubly degenerated parallel vibrations of H atoms, respectively. At intermediate coverage three loss peaks of 1138, 904 and 798 cm(-1) were obtained and attributed to symmetric, asymmetric and asymmetric stretching modes. This finding does not support earlier experimental investigations, but agrees well with recent HREELS analysis. Several models for the turn-around in work function change at half saturation coverage, such as adsorption site variation, bond length variation and surface buckling, were not confirmed by our calculations and a new explanation was provided. (C) 2005 Elsevier B.V. All rights reserved.