한명준 교수

We report an implementation of the $\mathrm{LDA}+U$ method based on the state-of-the-art linear combination of pseudo-atomic orbital (LCPAO) method, which is suitable for large-scale $\mathrm{O}(N)$ electronic structure calculations based on the density functional theory. By introducing a dual representation of the occupation number matrix instead of the on-site or full representations, the $\mathrm{LDA}+U$ formalism is refined to be consistent with a nonorthogonal LCPAO basis in regard to the s

Using first-principles density functional theory calculations combined with insight from a tight-binding representation, dynamical mean field theory, and linear response theory, we have extensively investigated the electronic structures and magnetic interactions of nine ferropnictides representing three different structural classes. The calculated magnetic interactions are found to be short range, and the nearest (J_{1a}) and next-nearest (J2) exchange constants follow the universal trend of J_{

Dynamical mean-field methods are used to calculate the phase diagram, many-body density of states, relative orbital occupancy, and Fermi-surface shape for a realistic model of LaNiO(3)-based superlattices. The model is derived from density-functional band calculations and includes oxygen orbitals. The combination of the on-site Hunds interaction and charge transfer between the transition metal and the oxygen orbitals is found to reduce the orbital polarization far below the levels predicted eith

To understand newly discovered superconductivity in Fe-based systems, we investigate the electronic structure and magnetic properties of Fe_{1+x}Te using first-principles density functional calculations. While the undoped FeTe has the same Fermi surface nested at (pi,pi) as in Fe arsenides, doping by approximately 0.5 electrons reveals a novel square-type Fermi surface showing a strong (pi,0) nesting and leading to a different magnetic structure. Our result strongly supports the same mechanism o

We report our first-principles calculations on multiferroic $\mathrm{Ga}\mathrm{Fe}{\mathrm{O}}_{3}$. The total energy results for different spin and structural configurations reveal that the ground state of $\mathrm{Ga}\mathrm{Fe}{\mathrm{O}}_{3}$ in its ideal structure is antiferromagnetic but it is likely to have a possible site disorder of Fe and Ga atoms between octahedral Ga sites and Fe sites, which is consistent with previous experimental observations. Examining the exchange interactions

The application of modern layer-by-layer growth techniques to transition-metal oxide materials raises the possibility of creating new classes of materials with rationally designed correlated electron properties. An important step toward this goal is the demonstration that electronic structure can be controlled by atomic composition. In compounds with partially occupied transition-metal $d$ shells, one important aspect of the electronic structure is the relative occupancy of different $d$ orbital

We report our first principles calculation studies of electronic structure and magnetic properties of the ${\mathrm{Mn}}_{n}$ $(n=4,12)$ single-molecule magnet, i.e., $[{\mathrm{Mn}}_{4}{\mathrm{O}}_{3}\mathrm{Cl}{(\mathrm{OAc})}_{3}{(\mathrm{dbm})}_{3}]$ $(\mathrm{dbmH}=\text{dibenzoyl}\text{\ensuremath{-}}\text{methane})$ and $[{\mathrm{Mn}}_{12}{\mathrm{O}}_{12}{({\mathrm{CH}}_{3}\mathrm{COO})}_{16}{({\mathrm{H}}_{2}\mathrm{O})}_{4}]$ molecules. For the calculations, we used the localized pse

Recent experimental findings of two dimensional ferromagnetism in Fe3GeTe2, whose critical temperature can reach room temperature by gating, has attracted great research interest. Here we performed elaborate ab initio studies using density functional theory, dynamical mean-field theory and magnetic force response theory. In contrast to the conventional wisdom, it is unambiguously shown that Fe3GeTe2 is not ferromagnetic but is antiferromagnetic, carrying zero net moment in its stoichiometric pha

Abstract Lattice distortion, spin interaction, and dimensional crossover in transition metal dichalcogenides (TMDs) have led to intriguing quantum phases such as charge density waves (CDWs) and 2D magnetism. However, the combined effect of many factors in TMDs, such as spin–orbit, electron–phonon, and electron–electron interactions, stabilizes a single quantum phase at a given temperature and pressure, which restricts original device operations with various quantum phases. Here, nontrivial polym

First-principles calculations predict that rotating one layer by 180° over the other layer can switch the interlayer magnetic order in bilayer CrI 3 , demonstrating stacking rotation as an effective strategy to manipulate the magnetism in 2D magnets.

Abstract Combining magnetism with band topology provides various novel phases that are otherwise impossible. Among several cases, noncollinear metallic antiferromagnets can reveal particularly rich topological physics due to their diverse magnetic ground states. However, there are only a few experimental studies due to the lack of suitable materials, especially with triangular lattice antiferromagnets. Here, we report that metallic triangular antiferromagnet Co 1/3 TaS 2 exhibits a substantial a

To investigate the electronic structure and magnetic properties of manganese oxide clusters, we carried out first-principles electronic structure calculations for small MnO clusters. Among various structural and magnetic configurations of the clusters, the bulklike [111]-antiferromagnetic ordering is found to be favored energetically, while the surface atoms of the clusters exhibit interesting electronic and magnetic characteristics which are different from their bulk ones. The distinct features

Abstract Herein, the synthesis of novel, highly luminescent, and nearly monodisperse zero‐dimensional (0D) cesium lanthanide chloride (Cs 3 LnCl 6 ; Ln = Y, Ce, Gd, Er, Tm, Yb) colloidal nanocrystals (NCs) is reported for the first time. The Cs 3 LnCl 6 NCs are synthesized using a heating‐up method and exhibit highly uniform size and shape. The monoclinic‐phase Cs 3 LnCl 6 NCs contain completely isolated [LnCl 6 ] 3− octahedral units, resulting in 0D ternary metal halide structures. Therefore, t

Abstract Magnetism in two-dimensional (2D) van der Waals (vdW) materials has lately attracted considerable attention from the point of view of both fundamental science and device applications. Obviously, establishing a detailed and solid understanding of their magnetism is the key first step toward various applications. Although Fe 3 GeTe 2 is a representative ferromagnetic (FM) metal in this family, many aspects of its magnetic and electronic behaviors still remain elusive. Here, we report our