In this thesis, the interactions of F...F in various complexes have been investigated. Although the interacting fluorines are completely identical, they connected by a bond path and hence a bond critical point. In the typical halogen bonds, one of the halogens plays the role of Lewis acid and the other one acts as a Lewis base. Since the charge, electrostatic potential and electron density distribution of the interacting fluorine atoms of the current work are identical, their interaction cannot be regarded as a Lewis acid-base interaction. So, the F…F interactions cannot be categorized as halogen bonds. Interacting quantum atom (IQA) analysis shows that the fluorine-fluorine interactions are repulsive in nature and destabilize the complex. Partitioning the interatomic interactions into Our IQA also show that, although the fluorine atoms are connected by bond baths, it is not responsible for the formation of their complexes. Instead, the secondary interactions (i.e. the interactions between not connected atoms) are the driving force for the complex formation. To compare the fluorine with the other halogens, the Cl...Cl and Br...Br have been also considered. Their IQA results show that, unlike to F…F interaction, chlorine-chlorine and bromine-bromine interactions are attractive. Here, the absolute value of exchange-correlation term is larger than classical repulsion. It should be mentioned the QTAIM parameters on the BCPs, predict that the F...F interactions are similar to Cl...Cl and Br...Br. Therefore, the results of this work questioned the ability of QTAIM parameters to predict chemical bond natures.
