  We investigate the influence of slab thickness on the electronic structure of
the Si(100)-p(2x2) surface in density functional theory (DFT) calculations,
considering both density of states and band structure. Our calculations, with
slab thicknesses of up to 78 atomic layers, reveal that the slab thickness
profoundly affects the surface band structure, particularly the dangling bond
states of the silicon dimers near the Fermi level. We find that, to precisely
reproduce the surface bands, the slab thickness needs to be large enough to
completely converge the bulk bands in the slab. In case of the Si(100) surface,
the dispersion features of the surface bands, such as the band shape and width,
converge when the slab thickness is larger than 30 layers. Complete convergence
of both the surface and bulk bands in the slab is only achieved when the slab
thickness is greater than 60 layers.
