In the first section of this thesis, the distribution of the Laplacian of electron density has been used to investigate the nature of tetrel bonds. Tetrel bonds are usually categorized as ?-hole interactio however, there are some evidence that indicate the failure of sigma-hole for describing these non-covalent interactions. Indeed, our NEDA, IQA and IQF calculations indicate that the classical electrostatic interactions play a secondary role in the formation of tetrel bonds. Accordingly, the ?-hole concept which is defined based on the classical electrostatic potential fails to interpret the nature of these bonds. Instead, the lump-hole concept uses the full quantum potential and provide a useful tool for describing tetrel bonds. According to this concept, a tetrel bond could be described as an interaction between a region with positive values of Laplacian of electron density (hole) in valance shell of charge concentration (VSCC) of tetrel center and a region of negative Laplacian (lump) in VSCC of Lewis base. In the second section, the nature of pnicogen bonds have been investigated with IQA, IQF and NEDA energy decomposition methods. According to results, the classical electrostatic potential plays a minor role in the stability and formation of these bonds. Similar to tetrel bonds, ?-hole concept is not useful for describing pnicogen bonds.
