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

Photovoltaic (PV) windows with shading devices benefit buildings in terms of power generation, daylighting control, glare protection, etc. In order to harvest the maximum solar energy from the window area, solar tracking is applied to the PV shading elements. The complicated movement trajectories and dynamic daylighting are difficult to simulate by conventional methods. In this work, we introduce an optical simulation method of daylighting in complex building environment using DIVA and Grasshopper, which are plugins of Rhinoceros, a commercial 3D computer graphics and computer-aided design (CAD) software. An algorithmic model of the PV blinds is built by Grasshopper based on amodified model of a reference office. Then DIVA is applied to evaluate the daylighting performance of the dynamic and static PV blinds. Simulation results show that the working plane reveals higher illuminance level and lower glare level with the dynamic PV blinds than that with their static counter parts. It is demonstrated that the proposed simulation method can deal with the daylighting evaluation of complex and dynamic building environment.

Daylighting simulation and analysis of buildings with dynamic photovoltaic window shading elements

The influence of deposition parameters on the growth of a-SiGe:H alloys in a plasma CVD system

Quantum wells (QWs) are nanostructures consisting of alternating layers of a low and high band-gap semiconductor. The band gap of QWs can be tuned by changing the thickness of the low band-gap layer, due to quantum confinement effects. Although this principle is well established for crystalline materials, there is still controversy for QWs fabricated from amorphous materials: How strong are the confinement effects in amorphous QWs, where, because of the disorder, the carriers are localized to start with? We prepare an atomistic model of QWs based on a-Si:H to gain insight into this problem. The electronic structure of our atomistic QWs model is described with first-principles density functional theory, allowing us to study the confinement effects directly. We find that the quantum confinement effect is rather weak, compared to experimental results on a similar system.

/pdf/quantum-confinement-and-band-offsets-in-amorphous-silicon-3n28x8d6c7.pdf

Quantum confinement and band offsets in amorphous silicon quantum wells

Light trapping accomplished by texturing of the wafer surface has produced a significant gain in solar cell performance of crystalline silicon solar cells. However, the continuous need of cost reduction requires the use of less raw material and cost-effective processes. To meet these requirements, more advanced light trapping schemes are needed. In this work we propose an approach for maximizing light absorption in thin silicon wafers. This light-trapping approach uses low cost and industrially scalable processes such as black silicon and random pyramids. The absorption measured on a series of thin silicon wafers was compared to single pass and Yablonovitch absorption limits. The electronic properties of wafers with the proposed light-trapping approach were also investigated.

Opto-electronic evaluation of thin double-textured crystalline silicon wafers

We report on an advanced modelling approach to accurately predict the energy yield of custom environment / urban integrated photovoltaic systems (E/UIPV). Several submodels are here presented, and their mutual interaction discussed. The flexibility of our software platform allows to exhaustively simulate custom horizons in combination with rigid/flexible PV modules and in presence of albedo component. In this respect, a modelling example predicts AC-side yield with <1% error on annual basis with respect to actual data. In addition, our platform can also deal with colored/bifacial modules and soiling losses for PV energy yield potential or performance prediction.

Miro Zeman

Papers

Daylighting simulation and analysis of buildings with dynamic photovoltaic window shading elements

The influence of deposition parameters on the growth of a-SiGe:H alloys in a plasma CVD system

Quantum confinement and band offsets in amorphous silicon quantum wells

Opto-electronic evaluation of thin double-textured crystalline silicon wafers

Advanced modelling of E/UIPV systems from location to load