Anomalous surface relaxation in hcp transition metals

First-principles total-energy calculations indicate anomalously large surface relaxations for groups IVA and VIIA hcp metals. In addition, for group VIIA elements the magnitude of the layer relaxation exhibits an unusually slow decay with the distance from the surface. We argue that the above phenomena can be traced back to the peculiar Fermi surface of groups IVA and VIIA hcp metals. Namely, the anomalous surface relaxation appears as a consequence of low-energy excitations with near 2k(F) wave vectors, which is also reflected by the flat and degenerate d bands located close to the Fermi level in the L-A-H plane of the hcp Brillouin zone.