Chemistry is a branch of physical science that studies the composition,structure,properties and change of matter.The chemical bond and reaction are core concepts of chemistry.The classifications of chemical bonds were traditionally based on the valence theory of Lewis,and are currently rely on molecular-orbital theory and valence-bond theory popularly.Electron Localization Functions(ELF)is a local quantum-mechanical functions related to the Pauli exclusion principle.Based on the ideas of Quantum Theory of Atoms in Molecules,the topological analysis of ELF provides 3 types of atrractors which correspond to bonding,non-bonding,core electron basins [1-2].