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.

Disulfuric acid dissociated by two water molecules: ab initio and density functional theory calculations.

Abstract: We have studied geometries, energies and vibrational spectra of disulfuric acid (H2S2O7) and its anion (HS2O7(-)) hydrated by a few water molecules, using density functional theory (M062X) and ab initio theory (SCS-MP2 and CCSD(T)). The most noteworthy result is found in H2S2O7(H2O)2 in which the lowest energy conformer shows deprotonated H2S2O7. Thus, H2S2O7 requires only two water molecules, the fewest number of water molecules for deprotonation among various hydrated monomeric acids reported so far. Even the second deprotonation of the first deprotonated species HS2O7(-) needs only four water molecules. The deprotonation is supported by vibration spectra, in which acid O-H stretching peaks disappear and specific three O-H stretching peaks for H3O(+) (eigen structure) appear. We have also kept track of variations in several geometrical parameters, atomic charges, and hybrid orbital characters upon addition of water. As the number of water molecules added increases, the S-O bond weakens in the case of H2S2O7, but strengthens in the case of HS2O7(-). It implies that the decomposition leading to H2SO4 and SO3 hardly occurs prior to the 2nd deprotonation at low temperatures.

Anharmonicity-Driven Rashba Cohelical Excitons Break Quantum Efficiency Limitation

Abstract: Closed-shell light-emitting diodes (LEDs) suffer from the internal quantum efficiency (IQE) limitation imposed by optically inactive triplet excitons. Here, an unrevealed emission mechanism of lead halide perovskites (LHPs) APbX3 (A = Cs/CN2 H5 ; X = Cl/Br/I) that circumvents the efficiency limit of closed-shell LEDs is explored. Though efficient emission is prohibited by optically inactive J = 0 in inversion symmetric LHPs, the anharmonicity arising from stereochemistry of Pb and resonant orbital-bonding network along the imaginary A+… X- (T1u ) transverse optical (TO) modes, breaks inversion symmetry, introducing disorder and Rashba-Dresselhaus spin-orbit coupling (RD-SOC). This results in bright cohelical and dark antihelical excitons. Many-body theory and first-principles calculations show that the optically active cohelical exciton is the lowest excited state in organic/inorganic LHPs. Thus, RD-SOC can drive to achieve the ideal 50% IQE by utilizing anharmonicity, much over the 25% IQE limitation for closed-shell LEDs.

Observation of Mg-induced structural and electronic properties of graphene

Abstract: We report the formation of superstructures induced by Mg adatoms on a single layer graphene (SLG) formed on Ni(111) substrate, where a strong metallic parabolic band is found near the Fermi level at the Γ-point of the Brillouin zone. Our valence band and core level data obtained by using synchrotron photons indicate that Mg adatoms intercalate initially to lift the SLG from the Ni substrate to produce a well-defined π-band of SLG, and then the parabolic band appears upon adding extra Mg atoms on the Mg-intercalated SLG. Our scanning tunneling microscopy images from these systems show the presence of superstructures, a 2√3 × 2√3 phase for the intercalated Mg layer below the SLG and then a √7 × √7 phase for the Mg overlayer formed on the Mg-intercalated SLG. We discuss the physical implications of these superstructures and the associated parabolic band in terms of a possible graphene-based two-dimensional superconductivity.

Energetics and pattern analysis of crystals of proflavine deoxydinucleoside phosphate complex

Abstract: Emploi de la methode de Monte Carlo suivant metropoles et de potentiels d'interaction de paires atome-atome ab initio pour l'etude du reseau des molecules d'eau autour du complexe 2:1 proflavine: desoxycytidylyl-3,5' guanosine. Bon accord avec les donnees structurales obtenues par diffraction de rayons X

Signature of a quantum dimensional transition in the spin- 1 2 antiferromagnetic Heisenberg model on a square lattice and space reduction in the matrix product state

Abstract: We study the spin-$\frac{1}{2}$ antiferromagnetic Heisenberg model on an $\ensuremath{\infty}\ifmmode\times\else\texttimes\fi{}N$ square lattice for even $N$'s up to 14. Previously, the nonlinear sigma model perturbatively predicted that its spin-rotational symmetry breaks asymptotically with $N\ensuremath{\rightarrow}\ensuremath{\infty}$, i.e., when it becomes two dimensional (2D). However, we identify a critical width ${N}_{c}=10$ for which this symmetry breaks spontaneously. It shows the signature of a dimensional transition from one dimensional (1D) including quasi-1D to 2D. The finite-size effect differs from that of the $N\ifmmode\times\else\texttimes\fi{}N$ lattice. The ground-state (GS) energy per site approaches the thermodynamic limit value, in agreement with the previously accepted value, by one order of $1/N$ faster than when using $N\ifmmode\times\else\texttimes\fi{}N$ lattices in the literature. Methodwise, we build and variationally solve a matrix product state (MPS) on a chain, converting the $N$ sites in each rung into an effective site. We show that the area law of entanglement entropy does not apply when $N$ increases in our method and the reduced density matrix of each effective site has a saturating number of dominant diagonal elements with increasing $N$. These two characteristics make the MPS rank needed to obtain a desired energy accuracy quickly saturate when $N$ is large, making our algorithm efficient for large $N$'s. Furthermore, the latter enables space reduction in MPS. Within the framework of MPS, we prove a theorem that the spin-spin correlation at infinite separation is the square of staggered magnetization and demonstrate that the eigenvalue structure of a building MPS unit of $\ensuremath{\langle}g|g\ensuremath{\rangle},|g\ensuremath{\rangle}$ being the GS is responsible for order, disorder, and quasi-long-range order.

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。