It has been considered that the surface atoms (ions) of the (100) face of a NaCl-type alkali halide are rumpled. In this review, it is described that the surface structure of solids can be estimated by the Kikuchi patterns of LEED in surface state resonance and of RHEED. The surface ions in MgO (001) lie in a plane in the as-cleaved face and are rumpled in the annealed face, in which the angle between the Mg-O bond direction and the (001) face is 3°