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

The III–V compound semiconductors play an important role for a variety of electronic and optoelectronic devices such as high electron mobility and heterostructure bipolar transistors, diode lasers, light-emitting diodes, photodetectors, electro-optic modulators, and frequency-mixing components. Apart from the binary compounds, ternary and quaternary alloys also may be combined within a countless variety of heterostructure configurations. The efficient exploitation of this flexibility requires, however, knowledge not only of the electronic properties of single compounds and alloys and their surfaces but also information on the band alignment of the respective interfaces. This motivates this article, which addresses the stoichiometrydependent band alignment at the GaxIn1 xP=AlyIn1 yP alloy interface. This interface occurs, e.g., in heterostructure solar cells and tandem absorber structures for the direct solar-tohydrogen conversion. GaP and AlP have indirect bandgaps of 2.34–2.35 and 2.5 eV, respectively, at zero temperature. In contrast, InP is a direct-gap semiconductor with a lowtemperature bandgap of 1.42 eV. According to photoluminescence data, the Ga content of GaxIn1 xP at the direct–indirect bandgap crossover is at about x1⁄4 0.71. Measurements for AlyIn1 yP indicate the direct–indirect crossover for y1⁄4 0.41, whereas recent density functional calculations place it at y1⁄4 0.48. To the best of our knowledge, there are neither experimental nor theoretical data available on the relative positions of the valence band maxima (VBM) and conduction band minima (CBM) at the GaxIn1 xP=AlyIn1 yP alloy interface, apart from valence band offsets at the binary end points. This article aims at closing this gap by providing band alignment values for the complete composition range. We focus here on the “natural” band lineups between unstrained materials obtained from the branch-point energies of the respective materials. They are determined here within hybrid density functional theory (DFT).

https://onlinelibrary.wiley.com/doi/pdf/10.1002/pssb.202000463

Band Alignment at Ga x In 1– x P/Al y In 1– y P Alloy Interfaces from Hybrid Density Functional Theory Calculations

The growth of GaN on the LiNbO3 (0001) surface is simulated by means of first-principles total-energy calculations. Firstly the adsorption of single N and Ga monolayers is investigated and then the layer-by-layer growth of GaN on the polar substrate within different orientations is modeled. While adsorbing a N layer does not heavily affect the substrate morphology, the adsorption of a Ga layer causes a rearrangement of the atomic structure. Furthermore the N layer is more strongly bound to the substrate than the Ga layer. On the basis of our results, we propose a microscopic model for the GaN/LiNbO3 interface. The GaN and LiNbO3 (0001) planes are parallel, but rotated by 30° each other, with in-plane epitaxial relationship [100]GaN II [110]. In this way the (0001) calculated in-plane lattice mismatch between GaN and LiNbO3 is minimal and equal to 6.79% of the GaN lattice constant. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN growth on LiNbO3 (0001) – a first‐principles simulation

http://homepages.uni-paderborn.de/wgs/Dpubl/SS307-309_235_1994.pdf

Coverage-dependent bonding of Sb on GaAs (110)

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Density-functional calculations based on finite-difference discretization and multigrid acceleration are used to explore the atomic and spectroscopic properties of P-rich InP(001)(2x1) surfaces grown in gas-phase epitaxy. These surfaces have been reported to consist of a semiconducting monolayer of buckled phosphorus dimers. This apparent violation of the electron counting principle was explained by effects of strong electron correlation. Our calculations show that the (2x1) reconstruction is not at all a clean surface: it is induced by hydrogen adsorbed in an alternating sequence on the buckled P-dimers. Thus, the microscopic structure of the InP growth plane relevant to standard gas-phase epitaxy conditions is resolved and shown to obey the electron counting rule.

Wolf Gero Schmidt

Papers

Band Alignment at Ga x In 1– x P/Al y In 1– y P Alloy Interfaces from Hybrid Density Functional Theory Calculations

GaN growth on LiNbO3 (0001) – a first‐principles simulation

Coverage-dependent bonding of Sb on GaAs (110)

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Gas-Phase Epitaxy Grown InP(001) Surfaces From Real-Space Finite-Difference Calculations