The spontaneous contraction only happens to bonds within the outermost two atomic spacings for a plane surface and could be more for nanocrystals to form the electron double layer . The NEP endows the undercoordinated atoms with exotic properties such as the single-atom catalytic activity and reactivity , edge superconductivity conductivity of topological insulators , and the high-TC superconductivity of monolayer , and the one-dimensional cuprite oxides. Bond contraction in the skin of 2.13 bond length stems from the size dependency of known properties such as bandgap, dielectric constant, mechanical strength, thermal stability, and magnetism . The H-O bond of fewer-coordinated water molecules follows the BOLS predicted trend, which elongates and polarizes the O:H nonbonding electrons.