First-principles study on the geometries and electronic structures of clean and hydrogen-adsorbed NbC(1 1 1) surface

The clean and hydrogen-adsorbed NbC(1 1 1) surfaces are investigated using the first-principles method. For the clean surface, the structural optimization shows that the spacing between the first and second layer is contracted obviously, and the electronic structure of relaxed surface are compared with the ideal surface. Five hydrogen-adsorption models are studied and the results indicate that the hydrogen atom prefers to be adsorbed on the threefold hollow site in which the third layer Nb atom sits directly below it. The H 1s-induced state is determined in the calculated band structure and the reason why this state cannot be observed in the ARPES is also presented in this work.