Strongly corelated electronic structure systems (SCSEs) have attracted much attention of researchers of academia and industry for a long time, because they exhibit unique and unusual properties never seen in other materials, such as High-Tc superconductivity, Seebeck effect, and magnetism. These unique and unusual properties of SCESs originate from their localized and corelated d and f electrons. Thus, to theoretically investigate SCESs, the first principles study of their d and f electrons is essential. The density functional (DFT) method based on the Kohn-Sham ansatz is inadequate and the DFT+U method is necessary, for the purpose. The DFT+U method describes the itinerant s and p electrons of SCESs by the DFT method and the localized and correlated d and f electrons of them by an approximate Hartree-Fock method, which considers the Hubbard-type on-site Coulomb and exchange interactions between d and f electrons. The DFT+U method uses parameters, U and J or Ueff (U-J). to describe the interactions between these electrons. The parameters of a SCES are usually determined, empirically, by finding those reproducing the lattice constant of the SCES but this approach does not work for a new SCES, for which experimental data are not available. A first principles calculation of these parameters is needed in this case. To make it possible, we have developed a method of calculating the effective Hubbard on-site interaction parameter (Ueff) used in the rotationally invariant density functional +U (DFT+U) theory of Dudarev et al.1 The method is based on the variation principle and can be used for the Ueff determination of several SCESs including rare-earth magnets. The DFT+U method of Dudarev et.al. becomes to satisfy the variation principles, completely, when it is used with the Ueff determined by our method. In this presentation, we explain the theoretical detail of our method and demonstrate its effectiveness, showing calculation results of Ueffs of some simple SCESs, namely neodymium sesquioxide (Nd2O3) and orthogonal iron oxide (FeO).

First principles calculation method of Hubbard-on-site interaction parameter

ACS Spring Meeting 2021

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