First-principles calculations of the energy dependent absorption coefficients are presented in this work in order to understand the optical properties of some materials characterized for an intermediate band (IB) with metallic behavior: Ga32P31Cr and Ga31P32Cr. The calculations are based on local spin density approximation and the pseudopotential method using a localized basis set. The resulting optical spectra is analyzed and broken down into the contributions of the different bands and spin components. The results of the electronic properties show that one of the spin components presents an IB, and the absorption coefficients indicate an increase in the absorption sub-gap as a consequence of the optical transitions between the valence and the IB. (c) 2005 Elsevier B.V. All rights reserved.