EQUILIBRIUM GEOMETRY AND ELECTRONIC-STRUCTURE OF THE LOW-TEMPERATURE W(001) SURFACE

The multilayer reconstruction of the W(001) surface at low temperature and the multilayer relaxation of the unreconstructed surface are investigated using first-principles total-energy and force calculations. The fully relaxed ideal surface is determined to be unstable by 110 meV per surface atom, which agrees qualitatively with results of previous studies where multilayer relaxation and reconstruction were not taken into account and supports the conclusion that the high-temperature phase is disordered. The lateral displacement of the second-layer atoms is about 18% that of the first-layer atoms and the first interlayer distance is contracted by about 6% from the bulk value in the reconstructed surface. The lateral displacements compare well with a recent x-ray-diffraction experiment. The electronic structure and the surface-state dispersions for the equilibrium reconstructed geometry are examined in detail.