was applied. The structures were fully relaxed using the Heyd-Scuseria-Ernzerhof (HSE06) hybrid DFT functional, except for lattice dynamics calculations (ionic contribution to dielectric constant, polar optical phonon (POP) frequency and phonon force constants) for which the Perdew-Burke-Ernzerhof generalized gradient approximation (GGA) functional for solids (PBEsol) was used. There are no constraints imposed on the unit cell shape or size, and relaxation continued until the change in maximum force on the ions and electronic free energy did not exceed 0.0005 eV/Å and 1×10 -8 eV, respectively. Electronic structure and high-frequency dielectric constant calculations used HSE06 including spin-orbit coupling (SOC) effects.