Role of double-hybrid density functionals and correlation consistent basis sets in OCS-hydrocarbon complexes

The role of five newly developed double hybrid density functionals (DHDFs) in conjunction with Dunning’s correlation consistent aug-cc-pVDZ, aug-cc-pVTZ and aug-cc-pVQZ basis sets has been investigated to describe the weak interaction of the T-shaped isomer of OCS-C2H2 and OCS-C2H4 weakly bound van der Waals (vdW) complexes. Structure, equilibrium distances, interaction, potential energy curves and binding energy or depth of the potential well of both the complexes have been studied in detail using the DHDFs theories with these basis sets. A comparison has been made between our present results and previous theoretical and experimental values. The potential energy curves are drawn to substantiate the calculated values. Calculated equilibrium distances are the same as those reported by experiments. The components of interaction energy of both the OCS-hydrocarbon complexes are also calculated using localized molecular orbital energy decomposition analysis. The results suggest that amongst the five DHDFs only the mPW2PLYP DHDF with aug-cc-pVQZ basis set gives the best results as compared to other DHDFs. The results provide an insight into the computational methods and basis sets for such weakly bound complexes. It also reveals that both method and basis set are important to obtain accurate results for such weakly bound complexes.