Comparative studies of the electronic structure of LiFePO4, FePO4, Li3PO4, LiMnPO4, LiCoPO4, and LiNiPO4

We report a comparative study of the electronic structures of LiFePO4, FePO4, Li3PO4, LiMnPO4, LiCoPO4, and LiNiPO4. We used the spin-polarized ab initio orthogonalized linear combinations of atomic orbitals method for the calculation. Li3PO4 is a large-band gap insulator with a band gap of 5.75 eV. For other crystals containing the 3d-transition metals (TM), the localized 3d bands of the TM fall within the large insulting gap. In the cases of FePO4 and LiMnPO4, the band gaps between the occupied majority spin band and the unoccupied minority spin band are of the order of 0.27 and 1.91 eV, respectively. For LiFePO4 and LiCoPO4, our calculation shows that they are 100% spin-polarized half metals. In the case of LiNiPO4, the Fermi level is in the small gap separating t2g and eg minority bands. These results are discussed in the context of the number of 3d electrons in the TM series and the possibility of strong electron correlation effects in these crystals.