Structural optimization was performed prior to running AIMD for the experimentally determined crystal structure (264 atoms) with a 1 × 1 × 2 k-point mesh. The cell parameters and all atomic positions were optimized from the crystal structure until the force acting on any atom was less than 5 ×10 -3 eV/ Å, which also satisfied the error in the total energy being less than 10 -4 eV. The PBE exchange-correlation functional cannot be used to obtain the correct vdW interactions resulting from charge fluctuations. A commonly used correction for this is the dispersion-corrected DFT (DFT-D3) of Grimme et al., which has been successfully used in molecular and solid crystalline materials. Structural optimization with DFT-D3 implemented in VASP was performed for comparison with the results of the structural parameters of the PBE exchange-correlation functional.