Abstract <p>This work presents a thorough analysis of the electronic, optical, and thermodynamic characteristics of ferromagnetic manganese selenide (MnSe) in both zinc-blende and rock-salt phases. Utilizing plane wave pseudo-potential calculations within the framework of spin-polarized density functional theory, our analysis offers a comprehensive evaluation. The calculated lattice parameters demonstrate a high level of concordance with available experimental data. Our findings indicate that MnSe compounds are semiconductors, as determined by their electronic band structures and density of states. Significant observations include the reduction in magnetic moments under increasing pressure, up to 10 GPa. Furthermore, we provide a detailed analysis of energy-dependent linear optical functions, including the complex dielectric function, complex refractive index, and reflectivity, and discuss their implications. Along with providing forecasts and in-depth discussions, our work clarifies the dependency of several thermodynamic variables on temperature and pressure for the compounds under investigation, including the bulk modulus, heat capacity, and thermal expansion coefficient.</p>