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 …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

We present a parameter-free method for an accurate determination of long-range van der Waals interactions from mean-field electronic structure calculations. Our method relies on the summation of interatomic C6 coefficients, derived from the electron density of a molecule or solid and accurate reference data for the free atoms. The mean absolute error in the C6 coefficients is 5.5% when compared to accurate experimental values for 1225 intermolecular pairs, irrespective of the employed exchangecorrelation functional. We show that the effective atomic C6 coefficients depend strongly on the bonding environment of an atom in a molecule. Finally, we analyze the van der Waals radii and the damping function in the C6R � 6 correction method for density-functional theory calculations.

/pdf/accurate-molecular-van-der-waals-interactions-from-ground-4sgen01nnb.pdf

Accurate molecular van der Waals interactions from ground-state electron density and free-atom reference data

There is still an ongoing effort to search for sustainable, clean and highly efficient energy generation to satisfy the energy needs of modern society. Among various advanced technologies, electrocatalysis for the oxygen evolution reaction (OER) plays a key role and numerous new electrocatalysts have been developed to improve the efficiency of gas evolution. Along the way, enormous effort has been devoted to finding high-performance electrocatalysts, which has also stimulated the invention of new techniques to investigate the properties of materials or the fundamental mechanism of the OER. This accumulated knowledge not only establishes the foundation of the mechanism of the OER, but also points out the important criteria for a good electrocatalyst based on a variety of studies. Even though it may be difficult to include all cases, the aim of this review is to inspect the current progress and offer a comprehensive insight toward the OER. This review begins with examining the theoretical principles of electrode kinetics and some measurement criteria for achieving a fair evaluation among the catalysts. The second part of this review acquaints some materials for performing OER activity, in which the metal oxide materials build the basis of OER mechanism while non-oxide materials exhibit greatly promising performance toward overall water-splitting. Attention of this review is also paid to in situ approaches to electrocatalytic behavior during OER, and this information is crucial and can provide efficient strategies to design perfect electrocatalysts for OER. Finally, the OER mechanism from the perspective of both recent experimental and theoretical investigations is discussed, as well as probable strategies for improving OER performance with regards to future developments.

Electrocatalysis for the oxygen evolution reaction: recent development and future perspectives

An accurate description of the two-electron density, crucial for magnetic coupling in spin systems, provides in general a major challenge for density functional theory calculations. It affects, e.g., the calculated zero-field splitting (ZFS) energies of spin qubits in semiconductors that frequently deviate significantly from experiment. In the present work (i) we propose an efficient and robust strategy to correct for spin contamination in both extended periodic and finite-size systems, (ii) verify its accuracy using model high-spin molecules, and finally (iii) apply the methodology to calculate accurate ZFS of spin qubits (NV$^-$ centers, divacancies) in diamond and silicon carbide. The approach is shown to reduce the dependence on the used exchange-correlation functional to a minimum.

Spin decontamination for magnetic dipolar coupling calculations: Application to high-spin molecules and solid-state spin qubits

Annihilation of delocalized positrons: a comparison of diamond and silicon

http://homepages.uni-paderborn.de/wgs/Dpubl/SS585_191_2005.pdf

Conformation-selective adsorption of 2,3-butanediol on Si(0 0 1)

Electron paramagnetic resonance (EPR) signatures, more specifically the elements of the electronic $g$ tensor, are calculated within density functional theory for hydrogenated Si(111), Si(001), Si(113), Si(114), $\mathrm{Si}(11\overline{2})$, and Si(110) surfaces. Thereby both perturbation theory and a more sophisticated Berry phase technique are applied. Specific defects on different surface orientations are shown to reproduce the resonances at $\overline{g}=2.0043$ and $\overline{g}=2.0052$ measured for hydrogenated microcrystalline silicon: The latter value is argued here to originate from regions with low hydrogen coverage; the resonance at $\overline{g}=2.0043$ is shown to appear in positions with dihydride environment, where an H atom is directly bound to the silicon dangling-bond atoms. A third group of EPR signals with considerably larger $\overline{g}$ values between 2.006 and 2.009 is predicted for highly symmetric dangling bonds resembling single dangling-bond defects in silicon bulk material. As the exact value depends strongly on local strain, this type of defect can explain a less intense signal with large $g$ strain observed in microcrystalline as well as in amorphous material.

Electron paramagnetic resonance calculations for hydrogenated Si surfaces

Ab-initio methods are applied to investigate the electronic and optical properties of lithium niobate-tantalate mixed crystals. Thereby the GW approach based on the electronic structure obtained within density functional theory is used to obtain the electron band structure including quasi-particle effects and the linear optical response is gained form the solution of the Bethe-Salpeter equation taking excitonic and local-field effects into account. Nonlinear optical coefficients are evaluated on the level of the independent-particle approximation. It is observed that increasing the tantalum amount widens the band gap and nearly linearly affects the optical birefringence. Also some second harmonic generation coefficients vary strongly with the stoichiometry.

/pdf/linb1-xtaxo3-electronic-structure-and-optical-response-from-7sfz4bawj6.pdf

Wolf Gero Schmidt

Papers

Spin decontamination for magnetic dipolar coupling calculations: Application to high-spin molecules and solid-state spin qubits

Annihilation of delocalized positrons: a comparison of diamond and silicon

Conformation-selective adsorption of 2,3-butanediol on Si(0 0 1)

Electron paramagnetic resonance calculations for hydrogenated Si surfaces

LiNb1-xTaxO3 Electronic Structure and Optical Response from First-Principles Calculations