The density functional theory (DFT) calculations were performed with the VASP software package using projector augmented plane wave method (PAW) pseduopotentials . The planewave energy cutoff was set to 530 eV. [46] The systems were iteratively relaxed until forces fell below 0.01 eV/ Å. The Brillouin zone was sampled with a Γ-centered Monkhorst-Pack k-point grid with a k-spacing of (1/15) Å-1 , which converged the lattice constants of HdabcoReO 4 to below 0.02 Å. Half this -spacing was used for obtaining elastic and piezoelectric coefficients using density functional perturbation theory (DFPT) . DFPT calculations provide piezoelectric coefficients e ij which links polarization and strain, as follows