In spite of the very large number of experiments (low-energy electron diffraction, Auger electron spectroscopy, UPS, MeV He+ scattering, work function, field-ion microscopy) carried out on W (100), no structural model consistent with all the data was proposed yet: in particular, the question of the reconstruction thermally induced when the sample was cooled below room temperature remains a puzzling problem. Furthermore, from a theoretical point of view, no definitive answer was given. Actually, either the mechanism invoked for the reconstruction was too weak, or some contributions were omitted or calculated without sufficient care. The authors compute here the surface energy of W (100) taking into account the band term treated in the tight binding approximation, a pair-wise repulsive potential of the Born-Mayer type and the electronic correlation contribution obtained from a perturbation treatment of the Hubbard model in the band limit. This energy was then fully minimised with respect to all coordinates of surface atoms, keeping all atoms neutral for any displacement. They find that the unreconstructed surface was the most stable at 0K and discuss this unexpected result. A similar calculation for Ta (100) led to opposite conclusions.

A Theoretical Inquiry into the Question of W and Ta (100) Atomic Structures. G.Treglia, M. C.Desjonqueres, D.Spanjaard: Journal of Physics C, 1983, 16[12], 2407-19