We describe the effect of many-particle corrections to improve the electronic energy spectrum calculated in the framework of the density functional formalism (DFF). We show that it is possible to consider an n-particle diagram like a correction to the DFF results for electronic structure, if we take into account the electron-electron interaction with nonzero transmitted momentum q or energy E. A model is proposed for calculating the leading term of the self-energy expansion as a power series in interactions, i.e. , the second-order term under the conditions q=0 and E&0. This model is illustrated by calculating the electronic band structure and optical properties of antiferromagnetic chromium.The self-energy correction leads to a better agreement between the theoretical calculations and experimental measurements of electronic properties.