Quantifying charge ordering by density functional theory: Fe3O4 and CaFeO3

We demonstrate that charge ordering can be quantitatively predicted by analyzing the Born effective charge (BEC), resolving the long-standing discrepancy between first-principles charge analysis and the nominal concepts of charge disproportionation in Fe3O4 and CaFeO3. In particular, the BEC differences between the disproportionated Fe ions are calculated to be similar to 2e, being in excellent agreement with the nominal charge separation in CaFeO3 while suggesting the charge disproportionation in Fe3O4 is understood by the charge separation similar to 2e instead of the nominal separation of similar to 1e. (C) 2014 Elsevier B.V. All rights reserved.