Density Functional Study on the Fundamental and Valence Excited States of Dibromine in T, P, and H Clathrate Cages

This work evaluates the performance of different DFT models in the accurate prediction of the guest-host intermolecular potentials for the ground and excited states of Br₂ in the tetrakaidecahedral (T), pentakaidecahedral (P), and hexakaidecahedral (H) clathrate cages. Of a set of density functionals, we found that PBE0-D3 and wb97XD provide a physically sound and quantitatively correct description of the interaction and transition energies of low-lying valence excited states of Br₂ inside these clathrate cages. The importance of correctly modeling dispersive interactions is also analyzed. This study provides the first detailed potential energy surface of the ground and excited states of Br₂ in the largest H cage. Comparisons with the LCC2 method and experimental electronic shifts probe the reliability of PBE0-D3 and wb97XD to describe weak intermolecular forces in the ground and excited states.