Abstract: The geometries and electronic structures of the (111) surfaces of some transition-metal carbides MC(M=Ti, Zr, V, Nb) have been investigated by using the first-principle methods. The results indicate that, compared to the ideal surface, the first layer (metal layer) and second layer (carbon layer) shift inwards and outwards respectively, and as a result, the space between the first and second layer is contracted. The results of the band structure calculation show that the main components of the surface state in DOS located near or crossed by EF are dxz/dyz orbitals of the surface metal atoms, and the influence of the surface relaxation on this state has been studied. In addition, discussions about the surface core-level shifts and the surface work functions are also presented.

Key words: Transition-metal carbides, Surface relaxation, Band structures, 　Surface state