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

A novel crystal configuration of sandwiched S-Mo-Se structure (Janus SMoSe) at the monolayer limit has been synthesized and carefully characterized in this work. By controlled sulfurization of monolayer MoSe2 the top layer of selenium atoms are substituted by sulfur atoms while the bottom selenium layer remains intact. The peculiar structure of this new material is systematically investigated by Raman, photoluminescence and X-ray photoelectron spectroscopy and confirmed by transmission-electron microscopy and time-of-flight secondary ion mass spectrometry. Density-functional theory calculations are performed to better understand the Raman vibration modes and electronic structures of the Janus SMoSe monolayer, which are found to correlate well with corresponding experimental results. Finally, high basal plane hydrogen evolution reaction (HER) activity is discovered for the Janus monolayer and DFT calculation implies that the activity originates from the synergistic effect of the intrinsic defects and structural strain inherent in the Janus structure.

Janus Monolayer Transition Metal Dichalcogenides

Fabricating 2D/2D heterojunction with vacancy is more favorable to the spatial separation and transfer of charge owing to the matching of unique 2D structure and vacancy engineering, but the regulation and observation of interlayer forces and electronic structure is a challenging task for synthesizing heterojunction photocatalyst and studying the photocatalytic hydrogen evolution mechanism Herein, an original 2D/2D ZnIn2S4/g-C3N4 Van der Waals heterojunction with S vacancies (ZIS-S/CN VDW) photocatalyst are firstly engineered The optimized 30ZIS-S/g-C3N4 has the highest H2 evolution rate of 60951 μmol h−1 g−1, which is primarily attributed to the fact that 2D/2D VDW heterojunction possesses larger contact area and strong electronic interaction to stimulate charge kinetics, and the vacancy engineering can enhance light absorption by regulating the electronic band structure and act as effective active sites for capturing electrons This work not only enriches 2D/2D heterojunction photocatalytic system based on g-C3N4, but also provides alternative proposal for engineering 2D/2D heterojunction photocatalyst with satisfactory performance

Synergy between van der waals heterojunction and vacancy in ZnIn2S4/g-C3N4 2D/2D photocatalysts for enhanced photocatalytic hydrogen evolution

The subject of thermal transport at the mesoscopic scale and in low-dimensional systems is interesting for both fundamental research and practical applications. As the first example of truly two-dimensional materials, graphene has exceptionally high thermal conductivity, and thus provides an ideal platform for the research. Here we review recent studies on thermal and thermoelectric properties of graphene, with an emphasis on experimental progresses. A general physical picture based on the Landauer transport formalism is introduced to understand underlying mechanisms. We show that the superior thermal conductivity of graphene is contributed not only by large ballistic thermal conductance but also by very long phonon mean free path (MFP). The long phonon MFP, explained by the low-dimensional nature and high sample purity of graphene, results in important isotope effects and size effects on thermal conduction. In terms of various scattering mechanisms in graphene, several approaches are suggested to control thermal conductivity. Among them, introducing rough boundaries and weakly-coupled interfaces are promising ways to suppress thermal conduction effectively. We also discuss the Seebeck effect of graphene. Graphene itself might not be a good thermoelectric material. However, the concepts developed by graphene research might be applied to improve thermoelectric performance of other materials.

Thermal and Thermoelectric Properties of Graphene

Electronic and optical properties of van der Waals heterostructures of g-GaN and transition metal dichalcogenides

First-principle study of electronic and optical properties of two-dimensional materials-based heterostructures based on transition metal dichalcogenides and boron phosphide

Recent investigations have revealed that some transition-metal dichalcogenides (TMDs), such as MoS2 and WS2, are excellent candidates for high-efficiency photocatalysts for water splitting. However...

First-Principles Study on Transition-Metal Dichalcogenide/BSe van der Waals Heterostructures: A Promising Water-Splitting Photocatalyst

We performed first-principles calculations of the structural, electronic, and optical properties of heterostructures which consist of transition metal dichalcogenides MX2 (M = Mo, W; X = S) stacked with Mg(OH)2. All the heterostructures are formed by van der Waals forces. The MoS2/Mg(OH)2 and WS2/Mg(OH)2 vdW heterostructures were found to be semiconductors with indirect bandgaps and possess intrinsic type-II band alignment. In particular, a comparison of the band edge positions with the redox potential of water indicates that the heterostructures are potential photocatalysts for water splitting, enabling water reduction on the MX2 layer and water oxidation on the Mg(OH)2 layer. Moreover, the photogenerated charges will be effectively separated in the presence of a large built-in electric field across the interface. In addition, all of the MX2/Mg(OH)2 heterostructures show strong optical absorption in the visible and infrared regions, indicating their promise for application in photocatalytic water splitting.

Transition-metal dichalcogenides/Mg(OH)2 van der Waals heterostructures as promising water-splitting photocatalysts: a first-principles study

https://iopscience.iop.org/article/10.1088/1361-6463/ab71ad/pdf

Kai Ren

Papers

Electronic and optical properties of van der Waals heterostructures of g-GaN and transition metal dichalcogenides

First-principle study of electronic and optical properties of two-dimensional materials-based heterostructures based on transition metal dichalcogenides and boron phosphide

First-Principles Study on Transition-Metal Dichalcogenide/BSe van der Waals Heterostructures: A Promising Water-Splitting Photocatalyst

Transition-metal dichalcogenides/Mg(OH)2 van der Waals heterostructures as promising water-splitting photocatalysts: a first-principles study

High-efficiency photocatalyst for water splitting: a Janus MoSSe/XN (X = Ga, Al) van der Waals heterostructure