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

Abstract

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 Br 2 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 Br 2 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 Br 2 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.

Interaction energy of Cl2 and Br2 with H2O: Exchange, dispersion and density the crucial ingredients

“…In previous work, we choose ω-B97X-D/aVTZ as a consistently good DFA for describing the interaction energy and the spectroscopic behavior of dihalogens inside clathrate cages. 15 In reproducing these smaller complexes, we confirm that its description of interaction energies and PES provides consistent results, albeit not perfect.…”

“…More recently, we have analyzed the performance of different DFA in describing this singular interaction aiming to study the spectroscopic properties of crystalline halogen hydrates systems beyond the single clathrate cage. Our first attempt was not very encouraging; however, a more detailed study suggested a couple of functionals as promising candidates for predicting the UV–vis transitions using the time‐dependent DFT 15 . However, since the correct description of the hydrate requires not only an accurate prediction of the vertical transitions but also the interaction with the cages and the dynamics of the guest inside, we were interested in confirming if, as the saying goes, we were getting the correct answer for the right reason.…”

“…Our first attempt was not very encouraging; however, a more detailed study suggested a couple of functionals as promising candidates for predicting the UV-vis transitions using the time-dependent DFT. 15 However, since the correct description of the hydrate requires not only an accurate prediction of the vertical transitions but also the interaction with the cages and the dynamics of the guest inside, we were interested in confirming if, as the saying goes, we were getting the correct answer for the right reason. This work aims to identify the best suited DFA for the study of halogens in aqueous environments and in the process understand the reasons behind the quality of the performance of some DFT approximations (DFA) in predicting the two individual interactions occurring between dihalogens and a water molecule: the halogen bond (XB), X-X -OH 2 , and the hydrogen-halogen interaction (HX), X-X -HOH.…”