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

Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Fast parallel algorithms for short-range molecular dynamics

Objective comparisons of electrocatalyst activity and stability using standard methods under identical conditions are necessary to evaluate the viability of existing electrocatalysts for integration into solar-fuel devices as well as to help inform the development of new catalytic systems. Herein, we use a standard protocol as a primary screen for evaluating the activity, short-term (2 h) stability, and electrochemically active surface area (ECSA) of 18 electrocatalysts for the hydrogen evolution reaction (HER) and 26 electrocatalysts for the oxygen evolution reaction (OER) under conditions relevant to an integrated solar water-splitting device in aqueous acidic or alkaline solution. Our primary figure of merit is the overpotential necessary to achieve a magnitude current density of 10 mA cm–2 per geometric area, the approximate current density expected for a 10% efficient solar-to-fuels conversion device under 1 sun illumination. The specific activity per ECSA of each material is also reported. Among HER...

Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices

介绍了Kirk—Othmer Encyclopedia of Chemical Technology（化工技术百科全书）（第五版）电子图书网络版数据库，并对该数据库使用方法和检索途径作出了说明，且结合实例简单地介绍了该数据库的检索方法。

Kirk-Othmer Encyclopedia of Chemical Technology数据库介绍及实例

Bismuth vanadate (BiVO4) has a band structure that is well-suited for potential use as a photoanode in solar water splitting, but it suffers from poor electron-hole separation. Here, we demonstrate that a nanoporous morphology (specific surface area of 31.8 square meters per gram) effectively suppresses bulk carrier recombination without additional doping, manifesting an electron-hole separation yield of 0.90 at 1.23 volts (V) versus the reversible hydrogen electrode (RHE). We enhanced the propensity for surface-reaching holes to instigate water-splitting chemistry by serially applying two different oxygen evolution catalyst (OEC) layers, FeOOH and NiOOH, which reduces interface recombination at the BiVO4/OEC junction while creating a more favorable Helmholtz layer potential drop at the OEC/electrolyte junction. The resulting BiVO4/FeOOH/NiOOH photoanode achieves a photocurrent density of 2.73 milliamps per square centimenter at a potential as low as 0.6 V versus RHE.

https://science.sciencemag.org/content/sci/early/2014/02/12/science.1246913.full.pdf

Nanoporous BiVO4 Photoanodes with Dual-Layer Oxygen Evolution Catalysts for Solar Water Splitting

Positron annihilation depth profiling is applied as a sensitive probe to investigate the defect evolution of hydrogenated amorphous silicon (a-Si:H) absorber layers fabricated by the PE-CVD method with typical thicknesses of 300-500 nm. The Doppler broadening lineshape parameter S of the layers was found to depend significantly on the applied hydrogen-to-silane flow ratio during their deposition, related to hydrogen-induced changes in the microstructure and local composition at the positron trapping site. Light-soaking degradation induces a time-dependent variation in the S parameter which seems to correlate with the evolution of defect densities extracted from FT-Photocurrent Spectroscopy measurements. (© WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Positron annihilation depth‐profiling as a promising tool for the structural analysis of light‐soaked a‐Si:H absorber layers

Impact of Interface Passivation on the Band Alignment of a-Si:H(n)/c-Si(p) Heterostructure Solar Cells

A unique hybrid degradation setup for CIGS solar cells

Computer modeling is used as a tool for determining current matching in hydrogenated amorphous silicon (a-Si:H) alloy tandem cells on textured substrates. The increasing complexity of a-Si:H based solar cells requires continuous extending and testing of the computer models which are used for their simulation. To take light scattering at the textured interfaces of the cell into account the authors developed a multi-rough-interface optical model GENPRO2 which was used for calculating the absorption profiles in the solar cells. The results of a sensitivity study of the parameters of this optical model such as the scattering coefficients of the reflected and transmitted light and the dependence of scattered light on the in-going and out-going angle are presented. In order to simulate multi-junction solar cell as a complete device they implemented a novel model for tunnel/recombination junction (TRJ), which combines the trap assisted tunneling and enhanced carrier transport in the high field region of the TRJ. The current matching conditions were determined both for a-Si:H and a-SiGe:H bottom cells, while the top cell was an a-Si:H cell. They investigated the influence of light scattering at the textured interfaces and of the thickness of the intrinsic layer of the bottom cell on themore » optimal ratio (i2/i1) between the thicknesses of the bottom (i2) and top (i1) intrinsic layers in the current-matched cell. The results show that increasing amount of scattering at the textured interfaces leads to higher efficiencies and lower ratio (i2/i1) in the current-matched cell. The use of a-SiGe:H material in the bottom cell leads to higher efficiency and 3 to 4 times lower i2/i1 ratio than in case of a-Si:H/a-Si:H cells.« less

Modeling of a-Si:H Alloy Solar Cells on Textured Substrates

The charge deep-level transient spectroscopy (Q-DLTS) experiments on undoped hydrogenated amorphous silicon (a-Si:H) demonstrate that during light soaking the states in the upper part of the gap disappear, while additional states around and below midgap are created. Since no direct correlation is observed in light-induced changes of the three groups of states that we identify from the Q-DLTS signal, we believe that we deal with three different types of defects. Positively charged states above midgap are related to a complex formed by a hydrogen molecule and a dangling bond. Negatively charged states below midgap are attributed to floating bonds. Various trends in the evolution of dark conductivity due to light soaking indicate that the kinetics of light-induced changes of the three gap-state components depend on their initial energy distributions and on the spectrum and intensity of light during exposure.

Miro Zeman

Papers

Positron annihilation depth‐profiling as a promising tool for the structural analysis of light‐soaked a‐Si:H absorber layers

Impact of Interface Passivation on the Band Alignment of a-Si:H(n)/c-Si(p) Heterostructure Solar Cells

A unique hybrid degradation setup for CIGS solar cells

Modeling of a-Si:H Alloy Solar Cells on Textured Substrates

Evolution of Charged Gap Statesin a - Si:H Under Light Exposure