Quantifying the Impact of Halogenation on Intermolecular Interactions and Binding Modes of Aromatic Molecules

Halogenationof aromatic molecules is frequently used to modulateintermolecular interactions with ramifications for optoelectronicand mechanical properties. In this work, we accurately quantify andunderstand the nature of intermolecular interactions in perhalogenatedbenzene (PHB) clusters. Using benchmark binding energies from thefixed-node diffusion Monte Carlo (FN-DMC) method, we show that generalizedKohn-Sham semicanonical projected random phase approximation(GKS-spRPA) plus approximate exchange kernel (AKX) provides reliableinteraction energies with mean absolute error (MAE) of 0.23 kcal/mol.Using the GKS-spRPA+AXK method, we quantify the interaction energiesof several binding modes of PHB clusters ((C6X6)( n ); X = F, Cl, Br, I; n = 2, 3). For a given binding mode, the interaction energies increase3-4 times from X = F to X = I; the X-X binding modeshave energies in the range of 2-4 kcal/mol, while the & pi;-& pi;binding mode has interaction energies in the range of 4-12kcal/mol. SAPT-DFT-based energy decomposition analysis is then usedto show that the equilibrium geometries are dictated primarily bythe dispersion and exchange interactions. Finally, we test the accuracyof several dispersion-corrected density functional approximationsand show that only the r2SCAN-D4 method has a low MAE and correctlong-range behavior, which makes it suitable for large-scale simulationsand for developing structure-function relationships of halogenatedaromatic systems.