The structure and UV spectroscopy of benzene–water (Bz–W6) clusters using time-dependent density functional theory

Abstract

DFT and MP2 calculations are performed to obtain optimized ground state geometries and binding energies of the cage and the prism conformers of water W₆ clusters and Bz–W₆ clusters using the aug-cc-pVDZ basis set. The cage conformer of Bz–W₆ system is found to be more stable than prism conformer for all range of DFT functionals and MP2. Time dependent-DFT is then used to study UV spectroscopy of Bz, water W₆ clusters and Bz–W₆ clusters at both the MP2 and wB97XD optimized ground state geometries using the B3LYP, CAM-B3LYP and M06-2X functionals with 6-31++G(d,p) and aug-cc-pVTZ basis sets. Our results predict minor differences in the UV spectroscopy of cage and prism conformers W₆ and Bz–W₆ clusters that may be observable with high-resolution spectroscopy. The M06-2X and CAM-B3LYP functionals perform consistently with each other. Benzene-mediated excitations of the water W₆ cluster towards longer wavelengths above 170 nm are noticed in both the cage and prism geometries of Bz–W₆. Benzene is found to be influenced after interacting with the cage and prism W₆ geometries, and is seen to undergo a red shift in the main π→π* electronic transition, in which the degeneracy is slightly broken. Charge transfer (CT) states and diffuse Rydberg-type states are also found to play an important role in the spectroscopy of such systems.