Halogen–Halogen Contacts in Bending Crystals: Limitations of QTAIM and NCI in Describing Sliding Energetics

The plastic bending behavior of isostructural hexachlorobenzene and hexabromobenzene crystals is governed by anisotropic intermolecular interactions, particularly halogen–halogen (Hal⋯Hal) contacts. This study critically evaluates the reliability of Quantum Theory of Atoms in Molecules (QTAIM) and Non-Covalent Interaction index analyses in capturing the energetic landscape of layer sliding along the bending (001) crystallographic plane. Energy profiles are calculated using periodic Density Functional Theory, gas-phase DFT, and the CrystalExplorer cluster-based approach. While all computational methods confirm the presence of a significant energy barrier to sliding, analysis of the interaction energy contributions computed with CrystalExplorer17 reveals that changes in the dispersion component are minimal (<2