The BOLS-NEP theory reconciling the attributes of undercoordinated adatoms, defects, surfaces and nanostructures

Abstract

This article describes a theory unifying the unusual performance of the undercoordinated adatoms, point defects, terrace edges, surfaces, and nanostructures of various shapes. The ideas of bond order-length-strength correlation and the associated nonbonding electron polarization (BOLS-NEP) feature that bonds between undercoordinated atoms contract spontaneously. Bond contraction raises the local density of charge and energy. Bond strength gain deepens the interatomic potential well to trap the core and bonding electrons deeply. In turn, the locally and densely entrapped electrons polarize those partially occupying the valence band and above pertaining to the lower-coordinated atoms. The BOLS-NEP theory reconciles the unusual behaviors of undercoordinated systems and the size dependency of nanostructures in their lattice oscillating dynamics, mechanical strength, thermal stability, photon emissivity, chemical reactivity, dielectric permeability, associated with generation of polarized Dirac fermions, serving as carriers for extraordinary catalysis, hydrophobicity, fluidity, lubricity, as well as monolayer high-T C superconductivity and topological insulator conductivity. • Atomic undercoordination shortens the local bonds and modifies the electron occupancy. • Nanocrystals prefer a core-shelled structure with a skin of two atomic layers thick. • Atomic cohesive energy dictates the thermal stability and the critical energy for phase transition. • Competition between energy density and cohesive energy transforms the Hall-Petch relationship. • Polarization dictates the catalysis, hydrophobicity, and monolayer high-T c superconductivity.