In the inner shells of atoms, lone pair regions, and covalent bond regions, electron localization is significantly higher than in surrounding areas, making it more difficult for electrons in these regions to delocalize. The ELF, proposed by Becke and Edgecombe in 1990, is a three-dimensional real-space function specifically designed to show electron localization in different regions of a chemical system. ELF is dimensionless, with a range of [0,1]. The closer the value is to 1, the stronger the electron localization at the corresponding position. ELF = 0.5 indicates electron localization similar to that of a non-interacting uniform electron gas. When plotting ELF, the focus is usually on regions where ELF > 0.5. In the valence region, if the ELF between two atoms is significantly greater than 0.5, it typically suggests a prominent covalent interaction between them, while regions with high ELF that do not appear between bonding atoms usually correspond to lone pairs or confined electrons. This section will not provide a detailed introduction to the background theory of ELF or a comprehensive overview of its wide applications. Interested readers are referred to the relevant reviews. The main aim of this section is to