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.

Large-scale polyol synthesis of single-crystal bismuth nanowires and the role of NaOH in the synthesis process.

Abstract: A modified polyol process is introduced for the production of single-crystal bismuth (Bi) nanowires with uniform diameters along each wire in relatively high yield. The appropriate amount of NaOH in the solution reacts with Bi(3+) to form water-soluble complexing ions BiO(2)(-). The tiny Bi nanoparticles formed at the initial stage could serve as seeds for the subsequent growth of Bi nanostructures in the refluxing process with the aid of PVP. We find that the amount of NaOH determines the reduction rate of BiO(2)(-), which influences the morphologies of the synthesized Bi nanostructures. High reduction rates result in nanowires and nanoparticles, while low reduction rates result in nanoplates.

Charge-transfer-to-solvent-driven dissolution dynamics of I- (H2O)2-5 upon excitation: excited-state ab initio molecular dynamics simulations

Abstract: In contrast to the extensive theoretical investigation of the solvation phenomena, the dissolution phenomena have hardly been investigated theoretically. Upon the excitation of hydrated halides, which are important substances in atmospheric chemistry, an excess electron transfers from the anionic precursor (halide anion) to the solvent and is stabilized by the water cluster. This results in the dissociation of hydrated halides into halide radicals and electron-water clusters. Here we demonstrate the charge-transfer-to-solvent (CTTS)-driven femtosecond-scale dissolution dynamics for I-(H2O)n=2-5 clusters using excited state (ES) ab initio molecular dynamics (AIMD) simulations employing the complete-active-space self-consistent-field (CASSCF) method. This study shows that after the iodine radical is released from I-(H2O)n=2-5, a simple population decay is observed for small clusters (2

Rashba–Dresselhaus Effect in Inorganic/Organic Lead Iodide Perovskite Interfaces

Abstract: Despite the imperative importance in solar cell efficiency, the intriguing phenomena at the interface between perovskite solar cell and adjacent carrier transfer layers are hardly uncovered. Here we show that PbI2/AI-terminated lead iodide perovskite (APbI3; A = Cs+/ methylammonium (MA)) interfaced with the charge transport medium of graphene or TiO2 exhibits a sizable/robust Rashba–Dresselhaus (RD) effect using density functional theory and ab initio molecular dynamics (AIMD) simulations above the cubic-phase temperature. At the PbI2-terminated graphene/CsPbI3(001) interface, ferroelectric distortion toward graphene facilitates an inversion breaking field. At the MAI-terminated TiO2/MAPbI3(001) interface, the enrooted alignment of MA+ toward TiO2 by short-strong hydrogen bonding and concomitant PbI3 distortion preserve the RD interactions even above 330 K. The robust RD effect at the interface even at high temperatures, unlike in bulk, changes the direct-type band to indirect-type to suppress recombinati...

La-doped BaSnO3 electron transport layer for perovskite solar cells

Abstract: Due to the photoinstability and large hysteresis of the TiO2 electron transport layer (ETL) in perovskite solar cells (PSCs), the search for novel electron transport materials has emerged. Herein, using first principles calculations, we unveiled the key factor for the ideal band alignment between La-doped BaSnO3 (LBSO) and methyl ammonium (MA) lead iodide perovskite (MAPbI3). The (PbI2-, MAI-terminated)CH3NH3PbI3/(SnO2-, BaO-terminated)LaxBa(1−x)SnO3 interface formed a stable “all-perovskite” heterostructure with large binding energy. The selective band alignment of the conduction band was easily manipulated by La-doping on the Ba site due to the band gap renormalization (or shrinkage) caused by doped electrons and La3+ dopant. In addition, the MAI-terminated MAPbI3/LBSO interface exhibited proton transfer (BaO-terminated) and strong hydrogen bonding (SnO2-terminated) between MA and oxygen anion. LBSO presenting high mobility, photostability, and structural stability would help develop the next generation ETL materials for PSCs.

Van der Waals isomers and ionic reactivity of the cluster system para-chlorofluorobenzene/methanol

Abstract: This combined experimental and computational study is aimed at elucidating the structure and reactivity of heterogeneous molecular clusters. We report results for the system para-chlorofluorobenzene/methanol (pClFB/MeOH). Particularly, three different van der Waals (vdW) isomers of the neutral (1:1) aggregate (π,σF,σCl) have been assigned by comparison of experimental infrared frequencies in the O–H and C–H stretch regions measured by IR/R2PI depletion spectroscopy with calculated frequencies at MP2/6-31+G(d) and B3LYP/6-31+G(d) level. The isomers are weakly hydrogen-bonded complexes with methanol’s OH group coordinated toward the aromatic π-electron cloud, the fluorine or the chlorine substituent, respectively. This assignment is corroborated by the UV and IR spectra of the corresponding monosubstituted benzene/methanol complexes. After resonant photoionization of pClFB⋅(MeOH)n, for n=1 besides vdW fragmentation, no chemical reactivity was observed for any isomer. The investigation of aggregates with n⩾5 indicated a substitution reaction taking place to produce chloroanisole+, emphasizing the importance of neutral precursor cluster size over cluster structure for intracluster ion–molecule reactions.

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。