arXiv subjects

Siheon Ryee

Publications and source records attributed to Siheon Ryee.

22 records · Page 2Linked to original sources

arXiv2018

The effect of double counting, spin density, and Hund interaction in the different DFT+$U$ functionals

A systematic comparative study has been performed to better understand DFT$+U$ (density functional theory + $U$) method. We examine the effect of choosing different double counting and exchange-correlation functionals. The calculated energy distribution and the Hund-$J$ dependence of potential profile for representative configurations clearly show the different behaviors of each DFT$+U$ formalism. In particular, adopting spin-dependent exchange-correlation functionals likely leads to undesirable magnetic solution. Our analyses are further highlighted by real material examples ranging from insulating oxides (MnO and NiO) to metallic magnetic systems (SrRuO$_3$ and BaFe$_2$As$_2$). The current work sheds new light on understanding DFT$+U$ and provides a guideline to use the related methods.

cond-mat.str-el↗

arXiv2018

Comparative study of DFT+$U$ functionals for non-collinear magnetism

We performed comparative analysis for DFT+$U$ functionals to better understand their applicability to non-collinear magnetism. Taking LiNiPO$_4$ and Sr$_2$IrO$_4$ as examples, we investigated the results out of two formalisms based on charge-only density and spin density functional plus $U$ calculations. Our results show that the ground state spin order in terms of tilting angle is strongly dependent on Hund $J$. In particular, the opposite behavior of canting angles as a function of $J$ is found for LiNiPO$_4$. The dependence on the other physical parameters such as Hubbard $U$ and Slater parameterization $F^4/F^2$ is investigated. We also discuss the formal aspects of these functional dependences as well as parameter dependences. The current study provides useful information and important intuition for the first-principles calculation of non-collinear magnetic materials.

cond-mat.str-el↗

arXiv2018

Charge density functional plus $U$ theory of LaMnO$_3$: Phase diagram, electronic structure, and magnetic interaction

We perform charge density functional theory plus $U$ calculation of LaMnO$_3$. While all the previous calculations were based on spin density functionals, our result and analysis show that the use of spin-unpolarized charge-only density is crucial to correctly describe the phase diagram, electronic structure and magnetic property. Using magnetic force linear response calculation, a long-standing issue is clarified regarding the second neighbor out-of-plane interaction strength. We also estimate the orbital-resolved magnetic couplings. Remarkably, the inter-orbital $e_g$-$t_{2g}$ interaction is quite significant due to the Jahn-Teller distortion and orbital ordering.

cond-mat.str-el↗

arXiv2017

Magnetic ground state of SrRuO$_3$ thin film and applicability of standard first-principles approximations to metallic magnetism

A systematic first-principles study has been performed to understand the magnetism of thin film SrRuO$_3$ which lots of research efforts have been devoted to but no clear consensus has been reached about its ground state properties. The relative t$_{2g}$ level difference, lattice distortion as well as the layer thickness play together in determining the spin order. In particular, it is important to understand the difference between two standard approximations, namely LDA and GGA, in describing this metallic magnetism. Landau free energy analysis and the magnetization-energy-ratio plot clearly show the different tendency of favoring the magnetic moment formation, and it is magnified when applied to the thin film limit where the experimental information is severely limited. As a result, LDA gives a qualitatively different prediction from GGA in the experimentally relevant region of strain whereas both approximations give reasonable results for the bulk phase. We discuss the origin of this difference and the applicability of standard methods to the correlated oxide and the metallic magnetic systems.

cond-mat.str-el↗