Kwang S. Kim

Bio: Kwang S. Kim is an academic researcher from Ulsan National Institute of Science and Technology. The author has contributed to research in topics: Ab initio & Graphene. The author has an hindex of 97, co-authored 642 publications receiving 62053 citations. Previous affiliations of Kwang S. Kim include Asia Pacific Center for Theoretical Physics & IBM.

Compositional and Dimensional Control of 2D and Quasi-2D Lead Halide Perovskites in Water

Abstract: Blue light emitting two dimensional (2D) and quasi-2D layered halide perovskites (LHPs) are gaining attention in solid-state lighting applications but their fragile stability in humid condition is one of the most pressing issues for their practical applications. Though water is much greener and cost effective, organic solvents must be used during synthesis as well as the device fabrication process for these LHPs due to their water-sensitivity/instability and consequently, water-stable blue-light emitting 2D and quasi-2D LHPs have not been documented yet. Here, water-mediated facile and cost-effective syntheses, characterizations, and optical properties of 16 organic–inorganic hybrid compounds are reported including 2D (A′)2PbX4 (A′ = butylammonium, X = Cl/Br/I) (8 compounds), 3D perovskites (4), and quasi-2D (A′)pAx−1BxX3x+1 LHPs (A = methylammonium) (4) in water. Here, both composition and dimension of LHPs are tuned in water, which has never been explored yet. Furthermore, the dual emissive nature is observed in quasi-2D perovskites, where the intensity of two photoluminescence (PL) peaks are governed by 2D and 3D inorganic layers. The Pb(OH)2-coated 2D and quasi-2D perovskites are highly stable in water even after several months. In addition, single particle imaging is performed to correlate structural–optical property of these LHPs.

Linear monatomic wires stabilized by alloying: Ab initio density functional calculations

Abstract: Using ab initio density functional calculations, we find that the monatomic AuZn and AuMg alloy wires have a truly linear structure as stable as the zig--zag one which is prone to form two-dimensional structures. The energy barrier between these two phases is about 0.7 eV for AuZn wire and 0.5 eV for AuMg wire. The injection of s electrons into the gold wire by zinc or magnesium lifts the Fermi level and the resulting $s--p$ hybridization yields an energy minima for the linear structure, which is further stablized by the polarization effect arisen from the enhanced atomic charges.

Tunable Photoluminescence across the Visible Spectrum and Photocatalytic Activity of Mixed-Valence Rhenium Oxide Nanoparticles

Abstract: Materials exhibiting excitation-wavelength-dependent photoluminescence, PL, are useful in a range of biomedical and optoelectronic applications. This paper describes a nanoparticulate material whose PL is tunable across the entire visible range and is achieved without adjusting particle size, any post-synthetic doping, or surface modification. A straightforward thermal decomposition of rhenium (VII) oxide precursor yields nanoparticles that comprise Re atoms at different oxidation states. Studies of time-resolved emission spectra and DFT calculations both indicate that tunable PL of such mixed-valence particles originates from the presence of multiple emissive states that become “active” at different excitation wavelengths. In addition, the nanoparticles exhibit photocatalytic activity that, under visible-light irradiation, is superior to that of TiO2 nanomaterials.

Direct emission from quartet excited states triggered by upconversion phenomena in solid-phase synthesized fluorescent lead-free organic–inorganic hybrid compounds

Abstract: We report, for the first time, the solid-phase gram-scale synthesis of two lead-free, zero-dimensional (0D) fluorescent organic–inorganic hybrid compounds, [Bu4N]2[MnBr4] (1) and [Ph4P]2[MnBr4] (2), achieved by grinding the organic and inorganic precursor salts. The solid-phase synthetic route has several advantages for modulating molecular dimensionalities. During grinding, organic cations and Mn2+ cations are co-crystallized together in the solid-state, forming a 0D assembly at the molecular level where each individual metal center is surrounded by organic cations. Both compounds exhibit an emission peak at 520 nm and a photoluminescence (PL) quantum yield (QY) of 47%. Here, we also report, for the first time, the upconversion phenomena which trigger different emission energies occurring in different quartet states of Mn, 4T1(4G), 4T2(4G), 4A1(4G), 4E(4G), 4T2(4D), 4E(4D), and 4T1(4P). These optical properties are unusual phenomena which break Kasha's rule of emission. Single particle imaging and low-temperature PL measurement are performed to obtain a deeper insight into these ground products. These results pave a new path to develop highly fluorescent non-toxic hybrid compounds with remarkable optical properties.

I and i

Abstract: There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality. Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials

Abstract: QUANTUM ESPRESSO is an integrated suite of computer codes for electronic-structure calculations and materials modeling, based on density-functional theory, plane waves, and pseudopotentials (norm-conserving, ultrasoft, and projector-augmented wave). The acronym ESPRESSO stands for opEn Source Package for Research in Electronic Structure, Simulation, and Optimization. It is freely available to researchers around the world under the terms of the GNU General Public License. QUANTUM ESPRESSO builds upon newly-restructured electronic-structure codes that have been developed and tested by some of the original authors of novel electronic-structure algorithms and applied in the last twenty years by some of the leading materials modeling groups worldwide. Innovation and efficiency are still its main focus, with special attention paid to massively parallel architectures, and a great effort being devoted to user friendliness. QUANTUM ESPRESSO is evolving towards a distribution of independent and interoperable codes in the spirit of an open-source project, where researchers active in the field of electronic-structure calculations are encouraged to participate in the project by contributing their own codes or by implementing their own ideas into existing codes.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。