First-principle theory on the relaxation configurations and electronic structures of Si(001) surface

For further studing the surface absorption and surface reaction for Si(001), the Si(001) surface was studied by using the first-principle method, and the equilibrium structure has been obtained by optimizing the structure; meanwhile, based on the optimum structure, the effects of variable vacuum layer thickness and slab thickness on the surface energies and surface atomic displacements were also studied. It shows that vacuum layer thickness and slab thickness have great influence on the surface energies and surface atomic displacements, respectively; if the slab thicknesses is at least 8 atom layers and the vacuum layer thickness is more than 1 nm, surface energies and surface atomic displacements tend to become convergent. In contrast with an ideal surface, the electronic structure of Si(001) surface and bonding characteristics change greatly under the influence of the surface relaxation. After the relaxation, system energy touches its minimum, and the structure becomes more stable.