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

Giant and isotropic magnetoresistance as huge as −53% was observed in magnetic manganese oxide La0.72Ca0.25MnOz films with an intrinsic antiferromagnetic spin structure. We ascribe this magnetoresistance to spin‐dependent electron scattering due to spin canting of the manganese oxide.

31p-S-4 Giant Magnetoresistance in Magnetic Manganese Oxide with Intrinsic Antiferromagnetic Spin Structure

A review on mechanics and mechanical properties of 2D materials—Graphene and beyond

Single‐Atom Catalysts for Electrocatalytic Applications

Recent progress in voltage control of magnetism: Materials, mechanisms, and performance

Ammonia (NH3) is one of the most significant industrial chemical products due to its wide applications in various fields. However, the production of NH3 from the electrochemical nitrogen (N2) reduction reaction (NRR) under ambient conditions is one of the most important issues that remain challenging for chemists. Herein, the candidacy of a series of molybdenum (Mo)-based single-atom catalysts (SACs) supported on N-doped black phosphorus (BP) as the electrocatalyst for the NRR has been evaluated by means of density functional theory (DFT) calculations. In particular, Mo1N3 has been found to chemically adsorb N2, and it exhibits the highest catalytic activity toward the NRR with an ultralow overpotential of 0.02 V via the associative distal mechanism, indicative of catalyzing the NRR under ambient conditions. Additionally, Mo1N3 shows the fast removal of the produced NH3 with a free energy uphill of only 0.56 eV and good stability of NRR intermediates. Moreover, the Mo-based SACs were demonstrated to be more selective to the NRR over the competing hydrogen evolution reaction (HER) process. These excellent features render Mo1N3 on BP as a compelling highly efficient and durable catalyst for electrochemical N2 fixation. Our results provide a rational paradigm for catalytic nitrogen fixation by SACs in two-dimensional (2D) materials under ambient conditions.

https://pubs.rsc.org/en/content/articlepdf/2019/nr/c9nr02586c

Single molybdenum center supported on N-doped black phosphorus as an efficient electrocatalyst for nitrogen fixation

In this letter, an oxide heterostructure has been fabricated by successively growing La0.7Sr0.3MnO3 and ZnO layers on a LaAlO3 (100) substrate using pulsed laser deposition. The ZnO∕La0.7Sr0.3MnO3 heterostructure exhibits good rectifying behavior and a positive colossal magnetoresistance (MR) effect over a temperature range of 77–280K. The maximum MR values are determined to be about 53.9% at H=0.5T and 36.4% at H=0.3T. A possible explanation is given in terms of the effect of magnetic fields on the depletion layer and the capture carriers effect at the interface.

Positive colossal magnetoresistance effect in ZnO∕La0.7Sr0.3MnO3 heterostructure

High‐performance, fully atomically dispersed single‐atom catalysts (SACs) are promising candidates for next‐generation industrial catalysts. However, it remains a great challenge to avoid the aggregation of isolated atoms into nanoparticles during the preparation and application of SACs. Here, the evolution of Pd species is investigated on different crystal facets of CeO2, and vastly different behaviors on the single‐atomic dispersion of surface Pd atoms are surprisingly discovered. In situ X‐ray photoelectron spectroscopy (XPS), in situ near‐ambient‐pressure‐XPS (NAP‐XPS), in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X‐ray absorption spectroscopy (XAS) reveal that, in a reducing atmosphere, more oxygen vacancies are generated on the (100) facet of CeO2, and Pd atoms can be trapped and thus feature atomic dispersion; by contrast, on the CeO2 (111) facet, Pd atoms will readily aggregate into clusters (Pdn). Furthermore, Pd1/CeO2(100) gives a high selectivity of 90.3% for the catalytic N‐alkylation reaction, which is 2.8 times higher than that for Pdn/CeO2(111). This direct evidence demonstrates the crucial role of crystal‐facet effects in the preparation of metal‐atom‐on‐metal‐oxide SACs. This work thus opens an avenue for the rational design and targeted synthesis of ultrastable and sinter‐resistant SACs.

Distinct Crystal‐Facet‐Dependent Behaviors for Single‐Atom Palladium‐On‐Ceria Catalysts: Enhanced Stabilization and Catalytic Properties

Combining atomistic simulations and continuum modeling, we studied dislocation shielding of a nanocrack in monolayer graphene under mode-I loading. Different crack-dislocation configurations were constructed and the shielding effects on the threshold stress intensity for crack propagation were examined. Excellent agreement between simulation results and linear-elastic fracture mechanics (LEFM) predictions was achieved. As the separation between the crack-tip and dislocation, that is, rR, varies (with respect to the crack size a), the shielding effect exhibits two different dependences on rR, scaling as 1/rR 1/2 for rR/a ≪ 1 (near-tip), whereas 1/rR for rR/a ≫ 1 (far-field), respectively. Particularly, the far-field 1/rR scaling was shown to be a direct manifestation of the stress field of dislocation in graphene. Our work presents a systematic study of nanoscale crackdislocation interactions in graphene, providing valuable information on defect engineering of graphene.

Dislocation Shielding of a Nanocrack in Graphene: Atomistic Simulations and Continuum Modeling.

Combining atomistic simulations and continuum modeling, a comprehensive study of the out-of-plane compressive deformation behaviors of equilateral three-dimensional (3D) graphene honeycombs was performed. It was demonstrated that under out-of-plane compression, the honeycomb exhibits two critical deformation events, i.e., elastic mechanical instability (including elastic buckling and structural transformation) and inelastic structural collapse. The above events were shown to be strongly dependent on the honeycomb cell size and affected by the local atomic bonding at the cell junction. By treating the 3D graphene honeycomb as a continuum cellular solid, and accounting for the structural heterogeneity and constraint at the junction, a set of analytical models were developed to accurately predict the threshold stresses corresponding to the onset of those deformation events. The present study elucidates key structure–property relationships of 3D graphene honeycombs under out-of-plane compression, and provides a comprehensive theoretical framework to predictively analyze their deformation responses, and more generally, offers critical new knowledge for the rational bottom-up design of 3D networks of two-dimensional nanomaterials.

Cheng Chen

Papers

Single molybdenum center supported on N-doped black phosphorus as an efficient electrocatalyst for nitrogen fixation

Positive colossal magnetoresistance effect in ZnO∕La0.7Sr0.3MnO3 heterostructure

Distinct Crystal‐Facet‐Dependent Behaviors for Single‐Atom Palladium‐On‐Ceria Catalysts: Enhanced Stabilization and Catalytic Properties

Dislocation Shielding of a Nanocrack in Graphene: Atomistic Simulations and Continuum Modeling.

Deformation behaviors of three-dimensional graphene honeycombs under out-of-plane compression: Atomistic simulations and predictive modeling