© 2022 Elsevier LtdThe main objective of this work is to highlight several physical behaviors of two new compounds (MgS2 and MgSe2) in the cubic structure of the Pa-3 space group, particularly their mechanical and dynamical stabilities, their electronic behaviors and to provide a detailed analysis of bonding between the different atoms and the identification of weak interactions that occur between unbonded atoms. The found results have shown that the two studied compounds are mechanically and dynamically stable, which confirms their presence in the Pa-3 space group structure. The values of the lattice parameter of both compounds are close to the theoretical comparison ones. 3D directional analysis of several mechanical quantities (E, G and υ) has shown that both compounds are elastically anisotropic. The study of the electronic properties has been carried out by TB-mBJ potential, which accurately estimates the band gap energy. The found results have shown that the value of the direct band-gap is close to that of the indirect one, which highlights the optoelectronic importance of these two new compounds. QTAIM analysis has shown that S-S and Se-Se bonds have a strong covalent character, while Mg-S and Mg-Se are ionic. Using the NCI method, weak interactions analysis has made it possible to locate all weak/strong interactions that exist in the structure of the two studied compounds and to identify their attractive/repulsive natures.