Visualization Analysis of Covalent and Noncovalent Interactions in Real Space

Understanding the types and locations of interactions between atoms or molecules within a chemical system is a fundamental concern in chemistry. In the field of theoretical and computational chemistry, wavefunction analysis offers various methods based on functions defined in 3D real space, enabling the visual representation of both covalent and noncovalent interactions. These methods provide researchers with an intuitive understanding of molecular interactions and are gaining increasing attention. This review systematically introduces various widely adopted and distinctive visualization methods, such as the noncovalent interaction (NCI) method, the independent gradient model based on Hirshfeld partition of molecular density (IGMH), the interaction region indicator (IRI), the electrostatic potential (ESP), the electron localization function (ELF), and deformation density. Additionally, numerous application examples are provided to help readers recognize the significant practical value of these methods. Also the computer program Multiwfn, which effectively implemented all the introduced methods, is briefly mentioned.