The character of the intermolecular interactions in Cl2-HX (X =F, Cl and Br) complexes has been investigated by means of the second-order Möller–Plesset perturbation theory (MP2) and the density functional theory (DFT) calculations. The results show that there are two types of lowest interaction potential equilibrium structures in the interactions between Cl2 and HX: X∙∙∙Cl type geometry and hy...