Charge order in Fe2OBO3: An LSDA+U study

Charge ordering in the low-temperature monoclinic structure of iron oxoborate Fe2OBO3 is investigated using the local spin density approximation LSDA+ U method. While the difference between t2g minority occupancies of Fe 2+ and Fe 3+ cations is large and gives direct evidence for charge ordering, the static “screening” is so effective that the total 3d charge separation is rather small. The occupied Fe 2+ and Fe 3+ cations are ordered alternately within the chain which is infinite along the a direction. The charge order obtained by LSDA+ U is consistent with observed enlargement of the angle. An analysis of the exchange interaction parameters demonstrates the predominance of the interribbon exchange interactions which determine the whole L-type ferrimagnetic spin structure.