Why UFe_xAl_12-x phase does not crystallize with ThMn₁₂-structure type, when x = 2?

The crystallographic structure of recently reported orthorhombic UFe ₂Al₁₀ phase, which belongs to the YbFe₂Al ₁₀-structure type is different from the well known tetragonal UFe_xAl_12-x (3 < x < 8) having ThMn ₁₂-structure type. Comparative Density Functional Theory (DFT) study of the relative stability of the orthorhombic UFe₂Al₁₀ phase with respect to different models of tetragonal ThMn₁₂-type structures with the same composition is carried out to explain this unusual phenomenon. It is shown that the fine interplay between the overlapping of 3d-states of Fe and 5f-states of U in the region -2.5 ÷ -0.3 eV below the Fermi energy dictates the lower total energy of orthorhombic UFe ₂Al₁₀ phase in comparison with tetragonal UFe ₂Al₁₀ phase crystallized in ThMn₁₂ structure. On the example of UFe₂Al₁₀ it is also directly demonstrated that DFT calculations in the framework of the Full Potential + Linear Augmented Plane Wave method within the local density approximation may be used for refining the structure of complicate compounds. The calculated equilibrium volume, lattice parameters and atomic Wyckoff positions of UFe ₂Al₁₀ intermetallic compound are in very good agreement with experimental data.