Modification of Cu-H bonding near a Ru(0001) surface

Surface linearized augmented plane wave (SLAPW) total energy calculations are used to study differences between Cu-H bonding on Cu(111) and on a pseudomorphic Cu monolayer on a Ru(0001) substrate. Bond lengths and vibration frequencies for {H(1 × 1)/ Cu(1 × 1) }/{Ru(0001) } versus {H(1 × 1) }/{Cu(111) } roughly obey an "effective medium" picture: the H atoms prefer to reside at a particular clean-surface charge density (0.013-0.015 au), and vibrate along the surface normal with a frequency, ω _⊥, proportional to the local, clean-surface normal charge density gradient. This results in a predicted 20% reduction of ω _⊥ on {Cu(1 × 1) }/{Ru(0001) } surface relative to ω _⊥ for Cu(111). At the same time, the weakening of the Cu-Cu bond when a Cu(111) layer is strained to fit pseudomorphically on Ru(0001) is partially compensated by the fact that the Cu-Ru bonding is stronger than Cu-Cu. Thus the binding energy of a H monolayer on {Cu(1 × 1) }/{Ru(0001) } is calculated to be only 0.05 {eV}/{H} greater than on Cu(111).