We studied the structural, electronic, and magnetic properties of Sm-doped Bi₂Se₃ using a GGA approximation in a frame of the fully relativistic spin-polarized Dirac linear muffin-tin orbital band-structure method. The X-ray absorption spectra (XAS) and X-ray magnetic circular dichroism at the Sm M4;5 edges were investigated theoretically from first principles. The calculated results are in good agreement with experimental data. The complex fine structure of the Sm M_4,5 XAS in Sm-doped Bi₂Se₃ was found to be not compatible with a pure Sm³⁺ valency state. The interpretation demands mixed valent states.