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 adsorption of single hydrogen atoms and hydroxyl radicals (OH) at the polar (0001) surface is simulated by means of first-principles total energy calculations, in order to investigate the influence of ferroelectric poling on the surface physics and chemistry of LiNbO3. H and OH are found to adsorb at a similar site both at the positive and at the negative (0001) surface. Despite this, the adsorption energy is for both adsorbates strongly polarization dependent, with adsorption energy differences as high as 2 eV. This striking contrast is traced back to electrostatic effects, which lead to a different bonding scenario at the two LN(0001) sides. The polar radical OH lies relatively flat on the positive surface, with the adsorbate oxygen forming a covalent bond with the surface oxygen. At the negative face, OH adsorbs roughly perpendicular and the adsorbate oxygen forms a bond of covalent nature with the surface cations. The adsorbate dipole moment is directed against the spontaneous polarization of the substrate. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Adsorption of OH and H at the LiNbO3(0001) surface

Atomic length-scale order characteristics of binary and ternary amorphous oxides are presented within the framework of ab initio theory. A combined numerically efficient density functional based tight-binding molecular dynamics and density functional theory approach is applied to model the amorphous (a) phases of SiO2 and TiO2 as well as the amorphous phase of atomically mixed TixSi1?xO2 hybrid-oxide alloys over the entire composition range. Short and mid-range order in the disordered material phases are characterized by bond length and bond-angle statistics, pair distribution function analysis, coordination number and coordination polyhedra statistics, as well as ring statistics. The present study provides fundamental insights into the order characteristics of the amorphous hybrid-oxide frameworks formed by versatile types of TiOn and SiOm coordination polyhedra. In a-SiO2 the fourfold crystal coordination of Si ions is almost completely preserved and the atomic structure is widely dominated by ring-like mid-range order characteristics. In contrast, the structural disorder of a-TiO2 arises from short-range disorder in the local coordination environment of the Ti ion. The coordination number analysis indicates a large amount of over and under-coordinated Ti ions (coordination defects) in a-TiO2. Aside from the ubiquitous distortions of the crystal-like coordinated polyhedra, even the basic coordination-polyhedra geometry type changes for a significant fraction of TiO6 units (geometry defects). The combined effects of topological and chemical disorder in a-TixSi1?xO2 alloys lead to a continuos increase in both the Si as well as the Ti coordination number with the chemical composition x. The important roles of intermediate fivefold coordination states of Ti and Si cations are highlighted for ternary a-TixSi1?xO2 as well as for binary a-TiO2. The continuous decrease in ring size with increasing Ti content reflects the progressive loss of mid-range order structure characteristics and the competing roles of network forming and network modifying SiOm and TiOn units in the mixed hybrid oxides.

The atomic structure of ternary amorphous TixSi1−xO2 hybrid oxides

We present first principles density functional theory calculations of three molecules, DEB and BuCYA, on a Au(111) surface. These molecules differ only in their side chains and have been observed to self-assemble in an ordered structure in the case of DEB but in a disordered structure in the case of BuCYA. Our calculations reveal the reason for this different behavior and explain recent STM-observations. The detailed analysis of the energetics underlines the importance of long-range dispersive interactions, which we find crucial to reproduce the experimental results.

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Wolf Gero Schmidt

Papers

Adsorption of OH and H at the LiNbO3(0001) surface

The atomic structure of ternary amorphous TixSi1−xO2 hybrid oxides

Role of Dihydrogen Bonds for the Stabilization of Self-Assembled Molecular Nanostructures

Water adsorbate influence on the Cu(110) surface optical response

3d core-level shifts at {Se}/{GaAs(110) }