Driving forces of the surface reconstructions: Mo and W(001) surfaces

A comparative study regarding to a driving mechanism for the reconstructions of the (001) surface of Mo and W is reported. A clear gap opening greater than 0.6 eV upon reconstruction for W(001) is sharply contrasted to the apparently no gapping for Mo(001). On the other hand, the curvature of the two dimensional Fermi surface contours drastically changes for Mo while remains almost unaltered for W. These data suggest that the reconstructions of these surfaces are two extreme cases driven essentially by a charge density wave mechanism.