Myung-Hwan Whangbo

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Quantum spin Hall (QSH) insulators exhibit a bulk insulting gap and metallic edge states characterized by nontrivial topology. We investigated the electronic structure of an isolated layer of methyl substituted germanane GeCH3 by density functional calculations (DFT), and its dynamic stability by phonon dispersion calculations. Our results show that an(More)
It is highly desirable to produce narrow-width graphene nanoribbons (GNRs) with smooth edges in large scale. In an attempt to solve this difficult problem, we examined the hydrogenation of GNRs on the basis of first principles density functional calculations. Our study shows that narrow GNRs can be readily obtained from wide GNRs by partial hydrogenation.(More)
Controlling amount of intrinsic S vacancies was achieved in ZnS spheres which were synthesized by a hydrothermal method using Zn and S powders in concentrated NaOH solution with NaBH4 added as reducing agent. These S vacancies efficiently extend absorption spectra of ZnS to visible region. Their photocatalytic activities for H2 production under visible(More)
Surface exchange and oxygen vacancy diffusion dynamics were studied in double-perovskites LnBaCo2O5.5+δ (LnBCO) single-crystalline thin films (Ln = Er, Pr; -0.5 < δ < 0.5) by carefully monitoring the resistance changes under a switching flow of oxidizing gas (O2) and reducing gas (H2) in the temperature range of 250 ~ 800 °C. A giant resistance change ΔR by(More)
In accounting for the magnetic properties of discrete and extended compounds with unpaired spins, it is crucial to know the nature of their ground and low-lying excited states. In this review we surveyed quantum mechanical descriptions on how these states are affected by spin-orbit coupling and attempted to provide a conceptual framework with which to think(More)
Triphylite-NaFePO4 is a cathode material for Na(+)-ion batteries, whereas its alternative polymorph maricite-NaFePO4 is not. These two different polymorphs exhibit widely different magnetic structures; the ordered magnetic structure of triphylite-NaFePO4 below ∼50 K is described by the propagation vector q1 = (0, 0, 0) with collinear spins, and that of(More)
First principles density functional theory calculations were carried out for the series of metal-rich compounds, LiPt(2), LiPt, and Li(2)Pt, and elemental Pt for comparison, to probe the bonding picture that captures the essence of their electronic structures. Our analysis shows that the 5d-electron configuration of Pt in these compounds is close to(More)
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