We propose a new approach to the calculation of ion populations in the LTE dense plasmas in the superconfiguration approximation. The screening of plasma ions is obtained using the same free-electron chemical potential for each ion charge. This chemical potential is determined by iteration keeping the total density constant and varying the volume of each ion. In such a way our approach not only gives the charge neutrality of the plasma, but also assures that the free-electron density is equal in the vicinity of each ion. The resulting ion charge distribution is different with respect to the one obtained without imposing the constraint of equal chemical potential. For instance, the effective charge is a little bit higher, which can change the shape of the absorption spectra, especially at higher densities. Examples of absorption spectra of medium-Z plasmas in a temperature and density range close to the present opacity measurements are shown.