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.

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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

The polymerization of tetraazaperopyrene (TAPP) molecules on a Cu(111) substrate, as observed in recent STM experiments, has been investigated in detail by first principles calculations. Tautomerization is the first step required for the formation of molecular dimers and polymers. The substrate is found to catalyze this tautomerization.

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Copper Substrate Catalyzes Tetraazaperopyrene Polymerization

The electronic and optical properties of the mixed-crystal system lithium niobate-tantalate has been calculated from first principles. Based on density functional theory we calculate the electronic properties including quasiparticle effects within the GW approach. The optical response including electron-hole attraction effects is obtained from the solution of the Bethe-Salpeter equation. While the band gap increase with increasing tantalum content and shows some bowing, a nearly linear dependence of the optical birefringence on the stochiometry is calculated.

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Lithium niobate-tantalate mixed crystals electronic and optical properties calculated from first principles

In the presentation of our results in Sec. III D, the numerical values of the ordinary (n⊥) and the extraordinary (n‖) refractive index were inadvertently reversed, affecting the discussion in the main text as well as the figures. Consequently, whenever we refer to our results for the ordinary refractive index or n⊥ in the original article, the extraordinary refractive index n‖ is actually meant, and vice versa. In the revised versions of Figs. 7 and 8 included here, the labels n⊥ and n‖ are now exchanged. Furthermore, we have taken this opportunity to incorporate improved convergence offsets in Fig. 7 that follow the procedure described at the beginning of Sec. III D and slightly raise the numerical values of the refractive indices compared to the original version. While the error does not affect the conclusions drawn from our results, the dependence of the refractive indices on the titanium concentration in Fig. 8 must be reinterpreted. We find that both the ordinary and extraordinary refractive index are approximately linear functions of the Ti concentration. Minor deviations from the linearity are due to the presence of pairs of Ti atoms situated closely along the crystal c axis in our structural models. Our calculations thus confirm the experimental finding [1,2] that, within the range of the investigated concentrations, the extraordinary refractive index is more strongly affected by Ti indiffusion than the ordinary refractive index. The experimentally observed concave behavior of the ordinary refractive index cannot be reproduced in our simulations due to the finite size of the supercells that can be treated with the required level of accuracy. Indeed, doping concentrations lower than 1.85 mol%, achieved using the larger 3×3×3 supercell, are currently not accessible. Moreover, other defect configurations, such as the substitution of NbLi antisites or NbNb by titanium atoms [3], might in fact be responsible for the experimentally observed deviation from the linear behavior.

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Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)]

The optical spectrum of water is not well-understood. For example, the main absorption peak shifts upwards by 1.3 eV upon condensation of gas-phase water monomers, which is contrary to the behaviour expected from aggregation-induced broadening of molecular levels. We investigate theoretically the effects of electron-electron and electron-hole correlation, finding that condensation leads to delocalisation of the exciton onto nearby hydrogen-bonded molecules. This reduces its binding energy and has a dramatic impact on the line shape. The calculated spectrum is in excellent agreement with experiment.

Anomalous Water Optical Absorption: Large-Scale First-Principles Simulations

: The adsorption of cyclic (alkyl) (amino) carbenes on the monohydride Si(001) surface is explored within density-functional theory. Two different adsorption mechanisms are investigated: the carbene insertion in Si − H bonds and the binding to a surface defect with missing hydrogen. The relative stability of these configurations depends on the hydrogen chemical potential, i.e., the surface preparation conditions as well as on the molecular side groups. The latter are also found to decisively influence the molecular diffusion. Some adsorption configurations are found to give rise to electronic states within the silicon bulk band gap. A sizable reduction of the work function is found upon molecular adsorption.

Wolf Gero Schmidt

Papers

Copper Substrate Catalyzes Tetraazaperopyrene Polymerization

Lithium niobate-tantalate mixed crystals electronic and optical properties calculated from first principles

Erratum: Optical properties of titanium-doped lithium niobate from time-dependent density-functional theory [Phys. Rev. Materials 1, 034401 (2017)]

Anomalous Water Optical Absorption: Large-Scale First-Principles Simulations

Adsorption of Cyclic (Alkyl) (Amino) Carbenes on Monohydride Si(001) Surfaces: Interface Bonding and Electronic Properties