  Surface reconstruction plays a vital role in determining the surface
electronic structure and chemistry of semiconductors and metal oxides. However,
it has been commonly believed that surface reconstruction does not occur in van
der Waals layered materials, as they do not undergo significant bond breaking
during surface formation. In this study, we present evidence that charge
density wave (CDW) order in these materials can, in fact, cause CDW surface
reconstruction through interlayer coupling. Using density functional theory
calculations on the 1T-TaS2 surface, we reveal that CDW reconstruction,
involving concerted small atomic displacements in the subsurface layer, results
in a significant modification of the surface electronic structure, transforming
it from a Mott insulator to a band insulator. This new form of surface
reconstruction explains several previously unexplained observations on the
1T-TaS2 surface and has important implications for interpreting surface
phenomena in CDW-ordered layered materials.
