Structure and dynamics of atomic hydrogen on NiAl(110)

Motivated by recent experiments we present an extensive theoretical study of structure and dynamics of hydrogen atomically adsorbed on the NiAl(110) surface. The study is performed in the framework of ab initio density-functional theory (DFT) molecular dynamics. DFT calculations indicate that at mono-layer coverage hydrogen adsorbs in slightly asymmetric positions near the Ni-Ni bridges and reduces the surface ripple present on the clean surface. At variance with recent electron energy-loss spectra (EELS) experiments which locate the hydrogen related vibrational features at anomalously low frequencies of 49.5 meV, present simulations indicate that hydrogen exhibits frequencies in the ordinary range of similar to130 meV but this feature remains hidden to the EELS probe due to very weak dipole moment. The possible nature and origin of the 49.5-meV feature is discussed.