See
(1) "The ELF Topological Analysis Contribution to Conceptual Chemistry and Phenomenological Models" in book "The Quantum Theory of Atoms in Molecules: From Solid State to DNA and Drug Design"
(2) Struct Bond (2016) 170: 213–248
My work "Revealing Molecular Electronic Structure via Analysis of Valence Electron Density" (http://www.whxb.pku.edu.cn/EN/10.3866/PKU.WHXB201709252) also contains application example of topology analysis of ELF.

Hi everyone! Please recommend literature that reviews the topological analysis of the ELF, LOL and Laplacian functions. The meaning of the critical points (3;+1), (3;-1) and (3;+3) in the context of these functions is not entirely clear