Strong Dependence of Point Defect Properties in Metal\nHalide Perovskites on Description of van der Waals Interaction

Weaker than ionic\nand covalent bonding, van der Waals (vdW) interactions\ncan have a significant impact on structure and function of molecules\nand materials, including stabilities of conformers and phases, chemical\nreaction pathways, electro-optical response, electron-vibrational\ndynamics, etc. Metal halide perovskites (MHPs) are widely investigated\nfor their excellent optoelectronic properties, stemming largely from\nhigh defect tolerance. Although MHPs are primarily ionic compounds,\nwe demonstrate that vdW interactions contribute ∼5% to the\ntotal energy, and that static, dynamics, electronic and optical properties\nof point defects in MHPs depend significantly on the vdW interaction\nmodel used. Focusing on widely studied CsPbBr<sub>3</sub> with the\ncommon Br vacancy and interstitial defects, we compare the PBE, PBE+D3,\nPBE+TS, PBE+TS/HI and PBE+MBD-NL models and show that vdW interactions\nstrongly alter the global and local geometric structure, and change\nthe fundamental bandgap, midgap state energies and electron-vibrational\ncoupling. The vdW interaction sensitivity stems from involvement of\nheavy and highly polarizable chemical elements and the soft MHP structure.