The paper by Liechtenstein, Anisimov, and Zaanen explores the role of orbital polarization in density-functional theory (DFT) for strongly interacting electron systems, particularly Mott-Hubbard insulators. They argue that orbital polarization should be treated on par with spin polarization and charge density. Using a basis-set independent generalization of the LDA+U functional, they demonstrate that orbital ordering is essential for accurately describing the crystal structure and exchange interaction parameters of the Mott-Hubbard insulator KCuF3. The authors highlight that the failure of local density approximation (LDA) in describing Mott-Hubbard insulators is due to the neglect of orbital polarization. They propose a minimal generalization of LDA+U that incorporates orbital ordering and treats both spin and orbital polarizations similarly to spin density. This functional is shown to be successful in describing various insulating 3d oxides and doped Mott-Hubbard insulators. In the context of KCuF3, the authors find that LDA fails to reproduce the observed lattice deformation, while the LDA+U functional correctly predicts the quadrupolar distortion and 1D antiferromagnetic ordering. They attribute these results to the inclusion of orbital-dependent interaction terms in the functional. The study emphasizes the importance of orbital polarization in understanding the electronic and structural properties of Mott-Hubbard insulators.The paper by Liechtenstein, Anisimov, and Zaanen explores the role of orbital polarization in density-functional theory (DFT) for strongly interacting electron systems, particularly Mott-Hubbard insulators. They argue that orbital polarization should be treated on par with spin polarization and charge density. Using a basis-set independent generalization of the LDA+U functional, they demonstrate that orbital ordering is essential for accurately describing the crystal structure and exchange interaction parameters of the Mott-Hubbard insulator KCuF3. The authors highlight that the failure of local density approximation (LDA) in describing Mott-Hubbard insulators is due to the neglect of orbital polarization. They propose a minimal generalization of LDA+U that incorporates orbital ordering and treats both spin and orbital polarizations similarly to spin density. This functional is shown to be successful in describing various insulating 3d oxides and doped Mott-Hubbard insulators. In the context of KCuF3, the authors find that LDA fails to reproduce the observed lattice deformation, while the LDA+U functional correctly predicts the quadrupolar distortion and 1D antiferromagnetic ordering. They attribute these results to the inclusion of orbital-dependent interaction terms in the functional. The study emphasizes the importance of orbital polarization in understanding the electronic and structural properties of Mott-Hubbard insulators.