Results are presented for a theoretical model, known as the ion model (IM), recently elaborated to calculate the radiative opacity of a hot dense plasma. The density functional theory is used to obtain the general set of self-consistent field equations that describe the state of the whole ensemble of plasma atoms and ions. Theoretical features of the Hartree–Fock–Slater model, the detail configuration account, and the IM are considered. The IM is used for optimal selections of compound chemical compositions for laser and heavy ion target designs.