New Hexagonal Ring Model for the Reconstruction of the Si(111)-7 × 7 Surface

An entirely new, very general, atomically smooth, and optically symmetry-adapted reconstruction model for the Si(111)-7×7 surface is proposed. It consists of parallel rows of nontouching, $\pi$-bonded, hexagonal rings with center atoms and seems to be a realization of a static commensurate phase of a nonlinear lattice. An overwhelming number of experimental findings on the Si(111) surface finds an intuitive, simple, and natural explanation by the model.