Comment on "Charge order in Fe2 OBO3: An LSDA+U study"

Abstract

In a recently published paper, Leonov present an LSDA+U study of the low temperature monoclinic structure of the iron oxoborate (Fe2 OBO3). 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 Fe3 O4. 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, Fe3 O4 and Fe2 OBO3, 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 Fe2 OBO3 does not show charge ordering. © 2006 The American Physical Society.