A theoretical investigation of electron–lattice interaction on Fe warwickites

Abstract

A theoretical electronic structure study is performed on two crystalline phases of the mixed valence, chargeordering Fe2OBO3 warwickite and on a V substituted compound,Fe1.91V0.09OBO3, known to exhibit no charge ordering or structural transitions. By using the extendedHückel method applied to the high spin band (hsb) filling scheme, calculations on bulk andon several crystal sub-units have shown that local monoclinic distortions leadto a decrease in Fe–Fe dimer interaction strength. It is suggested that changesin metal–metal interactions between two Fe sub-lattices stabilize local chargearrangements in the monoclinic phase, possibly set in through other effects such aselectrostatic long range interactions, discussed in the literature. The importance ofelectron–lattice interactions in charge localization and structural transition ofFe2OBO3 is further corroborated by calculations in the substituted compound, which show that Vacts so as to hinder inter-ribbon Fe–Fe interactions. It is also shown that the use of hsbgives very good results for the prediction of charge distribution in the pure and substitutedwarwickites.