The calculations are performed in Vienna Ab initio Simulation Package (VASP) thus the inputs and outputs files are in VASP format. Parts of the calculations concerning the Bethe-Salpeter equation use our own code that is not published. The data for publication is structured as follows: There are two main directories: (1) 1_Data_Sets_In_Paper contains the figures and grace files (which contain explicit data sets). The grace files can be opened using the xmgrace software, and arrays of data sets can be exported to txt files using xmgrace export functionality. (2) 2_VASP_and_BSE_IO contains the inputs for the VASP calculations performed in this work. Details will be discussed in the following section. DISCLAIMER: For the energy ranges discussed in the paper and presented in figures, optical spectra have been carefully calculated and converged. Outside of these energy ranges, however, there is no guarantee of the physicality of the results. Please be mindful of this when downloading data from the xmgrace files, and consult with the figures in the paper for the relevant energy range where results are physically meaningful. For further questions, please contact the authors. VASP_and_BSE_IO: Contains the explicit files related to VASP and the BSE code used in this study. POSCAR is the atomic structure, INCAR are setting for electronic structure calculations, and KPOINTS define the kmesh use to integrate over the Brillouin zone. Transmatrix files contain the transition dipole matrix elements between bands as a function of k-point. Details on file format can be found in the VASP manual at: https://cms f.mpi.univie.ac.at/vasp/vasp/vasp.html. (1): 1_Atomic_Structure contains, for each phase, the calculated ground state electronic structure needed to reproduce the results in this study. The DATA_X files (X indicates the phase) contain the energy v.s. volume curves used to confirm the stable ground state volume. (2): 2_Band_Structures contains the relevant files (VASP POSCAR, KPOINTS, INCAR) and band data to reproduce the band structures for each phase in this study. (3): 3_Density_of_States contains relevant files (VASP POSCAR, KPOINTS, INCAR) to reproduce the DOS for each phase in this study. (4): 4_GW0 contains the relevant files (VASP POSCAR, KPOINTS, INCAR) and QP eigenvalues to reproduce the prediction of the GW0 QP band gap for each phase found in this study. (5): 5_Optical_Spectra_and_BSE: This directory contains all relevant files to reproduce the optical response for each phase in this study. The two sub directories are detailed below. For others interested in reproducing the BSE results found herin, you will need to contact the authors for details in the code and implementation. (5a): shifted_kmesh: Coarse k-point meshes with random shifts are used to calculate optical spectra over a wide energy range. This directory contains three sub directories (C_SPEC_IO, T_SPEC_IO, and O_SPEC_IO, where C=cubic, T=tetragonal, and O=orthorhombic). The T and O directories only contains the SOC spectra IO, without BSE. The C_SPEC_IO contains SOC, EL, and FC directories. The SOC directory contains files to calculate the PBE+dGW0+SOC spectra without exciton effects on the shifted kmesh. The EL directory contains the IO for BSE+dGW0+SOC containing exciton effects and with interband electronic screening of the electron-hole Coulomb interaction only. The SPEC_OPP and SPEC_PAR files contain the spin conserving and spin-flip transitions spectra under SOC, respectively. The BSE folders contain IO for the BSE code used in this study. The FC directory contains the IO for BSE+dGW0+SOC containing exciton effects and with interband electronic screening PLUS Thomas-Fermi screening by additional free-electrons in the CB of the electron-hole Coulomb interaction. Similarly, it contains BSE run files (in the Wpar, Wopp, Vpar, Vopp, and CSC directories), and spectra output in the SPEC directories. Free electron concentrations are indicated by the presence of an FCX string in the file name, where X gives the free electron concentration in the CBM in cm^-3. (5b): hybrid_kmesh contains calculations using the hybrid k-point mesh technique to carefully sample the Brillouin zone around the band extrema. From hybrid mesh calculations we predict the converged exciton binding energies and the carefully sampled optical spectra around optical onset. Burstein-Moss shifts and band gap renormalization are also calculated on these grids. Similar to 5a, it contains C, T, and O subdirectories, where the O and T directories only include PBE+dGW0+SOC calculations. The C_IO directory contains both PBE+dGW0+SOC and BSE+dGW0+SOC calculations, and are arranged in the same structure as discussed in 5a.