Comment on “ Charge order in Fe 2 OBO 3 : An LSDA + U study ”

In a recently published paper Phys. Rev. B 72, 014407 2005 , Leonov et al. present an LSDA+U study of the low temperature monoclinic structure of the iron oxoborate Fe2OBO3 . They report on Fe2+-Fe3+ charge ordering without taking into account recent resonant x-ray scattering experiments, which demonstrate the lack of charge ordering in a closely related oxide such as Fe3O4. They propose that the charge ordering occurs between equivalent crystallographic sites. First, this result, apart from surprising, is at odds with basic concepts in condensed matter. Second, we argue on the reliability of this theoretical approach, showing that a strong discrepancy is obtained for the calculated total and d-projected charges at Fe atoms with formally the same valence state and local environment between two closed related compounds, Fe3O4 and Fe2OBO3, using the same theoretical method. Finally, we reconsider the reported theoretical calculations on the basis of a rigorous definition of the concepts of charge and orbital ordering and we show that Fe2OBO3 does not show charge ordering.