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

The effects of hot axisymmetric compression to break down the primary carbide network of the H23 tool steels were studied. This current study only focused on one strain rate of 0.01 s -1 . The samples were deformed at 3 different temperatures (1000, 1050 and 1100 o C) with solutioning temperatures 1100 and 1250 o C, respectively. Afterwards, the samples were cooled by water quenching. The techniques used in this current study for investigation were the optical and electron microscopes and Vickers hardness test. The results show that hot axisymmetric compression had broken down the primary carbide network in the direction perpendicular to the compression axis and the carbides became finer. Although the highest hardness (274 HV) was achieved after solutioning at 1250 o C, followed by deformation at 1000 o C, however the microstructure analysis indicated that the optimum hot axisymmetric compression condition was solutioning at 1250 o C and deformation at 1000 o C.

Advanced Materials Research

Novel methods and mechanisms for graphene fabrication are of great importance in the development of materials science. Herein, a facile method to directly convert carbonaceous salts into high‐quality freestanding graphene via a simple one‐step redox reaction, is reported. The redox couple can be a combination of sodium borohydride (reductant) and sodium carbonate (oxidant), which can readily react with each other when evenly mixed/calcined and yield gram‐scale, high‐quality, contamination‐free, micron‐sized, freestanding graphene. More importantly, this method is applicable to a variety of input reductants and oxidants that are low cost and easily accessible. An in‐depth investigation reveals that the carbonaceous oxidants can not only provide reduced carbon mass for graphene formation but also act as a self‐template to guide the polymerization of carbon atoms following the pattern of the monolayer, six‐carbon rings. In addition, the direct formation of graphene exhibits theoretically lower energy barriers than that of other allotropes such as fullerene and carbon nanotube. This facile, low‐cost, scalable, and applicable method for mass production of high‐quality graphene is expected to revolutionize graphene fabrication technology and boost its practical application to the industry level.

Reducing Carbonaceous Salts for Facile Fabrication of Monolayer Graphene

The electrochemical ammonia synthesis is an environmentally friendly method for ammonia production; however, it is still impeded by the bottleneck of N2 activation and challenging hydrogen evolution reaction (HER). A rational design for developing efficient electrocatalysts by tuning the surface electronic state is regarded as a promising strategy to overcome these obstacles. Herein, we report a phosphorus-doped potassium peroxyniobate (KNb3O8, denoted as P-KNO) electrocatalyst with enriched oxygen vacancies to effectively improve N2-to-NH3 efficiency and suppress HER. Such P-KNO electrocatalyst achieves a rate of 23.01 μg h-1 mgcat-1 for NH3 production at -0.45 V vs. reversible hydrogen electrode (RHE) and a faradaic efficiency (FE) of 39.77% at -0.4 VRHE in a 0.1 M Na2SO4 electrolyte, which is about twice that of the non-modified KNb3O8 (denoted as KNO, 11.35 μg h-1 mgcat-1, 19.60%) counterpart under the same condition. Moreover, the resultant P-KNO electrocatalyst renders steady NH3 yield amounts and selectivity in cycling tests for 10 h. It is concluded that the enhanced N2 fixation activity and faradaic efficiency are ascribed to the phosphorus doping and formation of oxygen vacancies, which not only make the surface of the electrocatalyst highly hydrophobic but also adjust the surface electronic structure of potassium niobate, thus resulting in accelerated N2 adsorption and activation during the NRR process. This electrocatalyst with phosphorus-doping and oxygen vacancies gives deep insights into the rational regulation of the surface electronic state of NRR electrocatalysts for efficient NH3 synthesis.

A phosphorus-doped potassium peroxyniobate electrocatalyst with enriched oxygen vacancies boosts electrocatalytic nitrogen reduction to ammonia.

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Catalytic Modification of Porous Two-Dimensional Ni-MOFs on Portable Electrochemical Paper-Based Sensors for Glucose and Hydrogen Peroxide Detection

Potassium chloride templated α-FAPbI3 perovskite crystal growth for efficient planar perovskite solar cells

Metal-organic framework materials own numerous significant merits as electrodes of sodium-ion batteries, such as multiple active sites and porous structure. However, the masked active sites and pores limit their performances....

Engineering the modulation of active sites and pores of pristine metal-organic frameworks for high-performance sodium-ion storage

Nanowelding system is set up to investigate the welding process of nickel electrodes to single walled carbon nanotubes (SWCNTs) with molecular dynamics method. This system consists of C-C, C-Ni, Ni-Ni subsystems. The interaction of C-C, C-Ni Ni-Ni are modeled by adaptive intermolecular reactive empirical bonder order (AIREBO) potential, Lennard-Jones (LJ) potential, as well as embedded atomic method (EAM) model respectively. The dynamic process of nanowelding at different temperatures and times is analyzed and described completely at atomistic length scales. The simulation results indicate that the nanowelding could be accomplished at 1450k which is far lower than the melting point of nickel.

Ya Rong Wang

Papers

Potassium chloride templated α-FAPbI3 perovskite crystal growth for efficient planar perovskite solar cells

Engineering the modulation of active sites and pores of pristine metal-organic frameworks for high-performance sodium-ion storage

Nanowelding of Single Walled Carbon Nanotubes onto Electrodes Using Molecular Dynamics Method

Interface Engineering Utilizing Bifunctional Metformin for High Performance Inverted Perovskite Solar Cells

Implementation of Structural and Surface Engineering Strategies to Copper Sulfide for Enhanced Sodium Ion Storage