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

We present a novel approach to solve the Bethe-Salpeter equation for the polarisation function. Rather than from the usual eigenvalue representation, the macroscopic polarisability is obtained from the solution of an initial-value problem. This allows for the first time to calculate excitonic and local-field effects in optical spectra of large and complex systems such as surfaces. As an example we investigate the optical anisotropy of the hydrogen-passivated Si(ll0) surface. It is shown that the electron-hole attraction is largely responsible for the peculiar line shape of the surface optical spectrum.

Excitonic and Local-Field Effects in Optical Spectra from Real-Space Time-Domain Calculations

We have performed total-energy pseudopotential calculations for a variety of structures for Al adsorbed on the GaAs(110) surface. For the coverage of one monolayer we find only very small differences of the adsorption energy for a number of competing structures. In contrast to recent LCAO calculations, we find all these structures to be either metallic or to have only a very small band gap. Total energy calculations are also made for a Ga-Al exchange reaction and for different structural models for half a monolayer coverage including a 2*1 reconstruction. In all cases we find the adsorption energy to be less than the cohesive energy of bulk Al in FCC structure or the energy gain due to an exchange reaction, indicating the tendency for cluster formation, as observed experimentally, or penetration into the substrate. By means of density-of-states calculations it is shown that the Schottky barrier is already formed for the ordered half-monolayer case and is completed for one monolayer of Al on GaAs. The band gap is found to open for an asymmetric dimer in a 2*1 reconstruction which may explain recent experimental observations.

https://iopscience.iop.org/article/10.1088/0953-8984/5/49/005/pdf

Chemisorption of aluminium on GaAs(110)

Rare earth induced silicide phases of submonolayer height and 5 × 2 periodicity on the Si(111) surface are investigated by density functional theory and ab initio thermodynamics. The most stable silicide thin film consists of alternating Si Seiwatz and honeycomb chains aligned along the [1\(\overline{1}\) 0] direction, with rare earth atoms in between. This thermodynamically favored model is characterized by a minor band gap reduction compared to bulk Si and explains nicely the measured scanning tunneling microscopy images.

Submonolayer Rare Earth Silicide Thin Films on the Si(111) Surface

Molecular dynamics simulations in the framework of the density functional theory are used for the first time in order to model the ferroelectric-paraelectric phase transition in LiNbO 3 . Our calculations show that the structural phase transition is not an abrupt event, but rather a continuous process occurring over about 100 K and involving different ionic species at different temperatures. Because of the different behavior of the Li and Nb sublattice, the ferroelectric transition displays both displacive and order-disorder character.

Ferroelectric phase transition in LiNbO 3 : Insights from molecular dynamics

Abstract Polarons influence decisively the performance of lithium niobate for optical applications. In this work, the formation of (defect) bound polarons in lithium niobate is studied by ab initio molecular dynamics. The calculations show a broad scatter of polaron formation times. Rising temperature increases the share of trajectories with long formation times, which leads to an overall increase of the average formation time with temperature. However, even at elevated temperatures, the average formation time does not exceed the value of 100 femtoseconds, i.e., a value close to the time measured for free, i.e., self-trapped polarons. Analyzing individual trajectories, it is found that the time required for the structural relaxation of the polarons depends sensitively on the excitation of the lithium niobate high-frequency phonon modes and their phase relation. 

/pdf/bound-polaron-formation-in-lithium-niobate-from-ab-initio-s55oloab.pdf

Wolf Gero Schmidt

Papers

Excitonic and Local-Field Effects in Optical Spectra from Real-Space Time-Domain Calculations

Chemisorption of aluminium on GaAs(110)

Submonolayer Rare Earth Silicide Thin Films on the Si(111) Surface

Ferroelectric phase transition in LiNbO 3 : Insights from molecular dynamics

Bound polaron formation in lithium niobate from ab initio molecular dynamics