Effect of external electric field on the electronic structure of ferrite using the density functional theory simulation

In this work, the electronic structure of three ferrites, Fe2O3 (hematite), Fe3O4 (magnetite), and alpha-FeOOH (goethite), have been calculated with the density functional theory (DFT) under external electric field (E) for investigating the effect of the external electric field on the electronic structure of ferrites. It was found that the external electric field could continue to decrease the band gap by 0.36, 0.12, and 0.34 eV under an E of 0.01 V.nm(-1) through signally changing the valance band maximum. When it increased to 0.1 V.nm(-1), Fe2O3 would be broken down by the external electronic field, causing a breaking of the Fe-O bond and a delocalization among Fe atoms along the E direction. At the same time, Fe3O4 and alpha-FeOOH could maintain their crystal with some effect on the localization and energy of the electron. In addition, it showed a degeneration of the valance electron for three ferrites under the external electric field. For Fe2O3, the Hirshfeld charge of the Fe atoms was reduced while improved for the O atoms along with an increase in the external electronic field. Interestingly, the Hirshfeld charge for both Fe atoms with the form charge of +2 and +3 in Fe3O4 was not influenced by the external electronic field. As for alpha-FeOOH, the unit of FeO6 located on the edge of the chain was more sensitive than that of the body FeO6 in the chain towards the external electronic field. Meanwhile, the H atom of the terminated -OH in alpha-FeOOH exhibited a disproportionated response on the Hirshfeld charge under the external electronic field. With the spin of electrons in ferrites, increasing the external electronic field would improve the spin of electrons in Fe3O4 while reducing it in alpha-FeOOH among an E of 0.001-0.1 V.nm(-1).