Txt files containing the dielectric function of bulk single crystal c-axis oriented 2H-GaS (gallium sulfide) both experimental and DFT calculated values. EXPERIMENTAL GaS_bulk_experimental.txt Experimental value of the dielectric function obtain through spectroscopic ellipsometry under the isotropic assumption. DFT CALCULATED DFT calculations on bulk GaS were performed with SIESTA (https://siesta-project.org/siesta/). The two components of the dielectric tensor of GaS were calculated. in-plane component (E || c-axis): GaS_inplane_epsilon_img.dat and GaS_inplane_epsilon_real.dat out-of-plane component (E ⊥ c-axis): GaS_outofplane_epsilon_img.dat and GaS_outofplane_epsilon_real.dat