Importance of intersite Hubbard interactions in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>β</mml:mi><mml:mtext>−</mml:mtext><mml:msub><mml:mrow><mml:mi>MnO</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:math>: A first-principles <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>DFT</mml:mi><mml:mo>+</mml:mo><mml:mi>U</mml:mi><mml:mo>+</mml:mo><mml:mi>V</mml:mi></mml:mrow></mml:math> study
Ruchika Mahajan, Iurii Timrov, Nicola Marzari, Arti Kashyap
Abstract
We present a first-principles investigation of the structural, electronic, and magnetic properties of pyrolusite ($\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Mn}{\mathrm{O}}_{2}$) using conventional and extended Hubbard-corrected density-functional theory ($\mathrm{DFT}+U$ and $\mathrm{DFT}+U+V$). The onsite $U$ and intersite $V$ Hubbard parameters are computed using linear-response theory in the framework of density-functional perturbation theory. We show that while the inclusion of the onsite $U$ is crucial to describe the localized nature of the $\mathrm{Mn}(3d)$ states, the intersite $V$ is key to capture accurately the strong hybridization between neighboring $\mathrm{Mn}(3d)$ and $\mathrm{O}(2p)$ states. In this framework, we stabilize the simplified collinear antiferromagnetic (AFM) ordering (suggested by the Goodenough-Kanamori rule) that is commonly used as an approximation to the experimentally-observed noncollinear screw-type spiral magnetic ordering. A detailed investigation of the ferromagnetic and of other three collinear AFM spin configurations is also presented. The findings from Hubbard-corrected DFT are discussed using two kinds of Hubbard manifolds---nonorthogonalized and orthogonalized atomic orbitals---showing that special attention must be given to the choice of the Hubbard projectors, with orthogonalized manifolds providing more accurate results than nonorthogonalized ones within $\mathrm{DFT}+U+V$. This paper paves the way for future studies of complex transition-metal compounds containing strongly localized electrons in the presence of pronounced covalent interactions.