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

Simultaneously increasing the activity and stability of the single-atom active sites of M-N-C catalysts is critical but remains a great challenge. Here, we report an Fe-N-C catalyst with nitrogen-coordinated iron clusters and closely surrounding Fe-N4 active sites for oxygen reduction reaction in acidic fuel cells. A strong electronic interaction is built between iron clusters and satellite Fe-N4 due to unblocked electron transfer pathways and very short interacting distances. The iron clusters optimize the adsorption strength of oxygen reduction intermediates on Fe-N4 and also shorten the bond amplitude of Fe-N4 with incoherent vibrations. As a result, both the activity and stability of Fe-N4 sites are increased by about 60% in terms of turnover frequency and demetalation resistance. This work shows the great potential of strong electronic interactions between multiphase metal species for improvements of single-atom catalysts. 

/pdf/iron-atom-cluster-interactions-increase-activity-and-improve-30e9hnqy.pdf

Iron atom–cluster interactions increase activity and improve durability in Fe–N–C fuel cells

Multilayer in-plane graphene/hexagonal boron nitride heterostructures: Insights into the interfacial thermal transport properties

A review of state of the art thermal diodes and their potential applications

Remarkably reduced thermal contact resistance of graphene/olefin block copolymer/paraffin form stable phase change thermal interface material

This study uses non-equilibrium molecular dynamics simulations to investigate the impact of antisite substitution on thermal conductivity. The phonon-dispersion curve and predicted thermal conductivity of pristine hexagonal boron nitride nanosheets (hBNNSs) show good agreement with the experiment results, indicating the reliability of the extep potential. It is clear that both neighboring substitution (NS) and random substitution (RS) drastically reduce the thermal conductivity of hBNNSs, of which RS has a larger effect. Calculations for the participation ratio and relaxation time show that the localization is the primary cause for the reduction in thermal conductivity when the defect concentration is low. When the defect concentration is higher, the primary cause is phonon-defect scattering in all phonon modes. RS has a larger effect on the phonon modes with long mean free paths, while NS has a larger effect on phonon modes with various lengths of mean free paths.

Phonon transport in antisite-substituted hexagonal boron nitride nanosheets: A molecular dynamics study

Interfacial Thermal Conductance of BP/MoS2 van der Waals Heterostructures: an Insight from the Phonon Transport


 The in-plane graphene/hexagonal boron nitride (Gr/h-BN) heterostructures have received extensive attention in recent years due to their excellent physical properties and the development potential of next-generation nanoelectronic devices. Generally, different bonding types between Gr and h-BN are considered in different non-equilibrium molecular dynamics (NEMD) simulations studies. However, which type of bonding is most conducive to interface thermal transport is still very confusing. In this work, we investigate the interfacial thermal conductance (ITC) and the thermal rectification (TR) in five different bonding types of in-plane Gr/h-BN heterostructures by using NEMD simulations. It is found that the ITC depends strongly on the bonding strength and arrangement of different atoms across the boundary. Among the five different bonding types of heterostructures, the C-N bonded heterojunction exhibits the highest ITC due to its stronger interfacial bonding. The analyses on the strain distribution indicated that a low interfacial stress level at the interface junction, may facilitate the heat conduction, thus leading to a higher ITC. In addition, we found that TR occurs in all five bonded heterostructures, and the C-B bonded heterojunction possesses the highest TR factor. The present study is of significance for understanding the thermal transport behavior of Gr/h-BN heterostructures and promoting their future applications in thermal management and thermoelectric devices.

Interfacial Thermal Conductance and Thermal Rectification Across In-Plane Graphene/h-BN Heterostructures With Different Bonding Types

Thermal resistance at a soft/hard material interface plays an undisputed role in the development of electronic packaging, sensors, and medicine. Adhesion energy and phonon spectra match are two crucial parameters in determining the interfacial thermal resistance (ITR), but it is difficult to simultaneously achieve these two parameters in one system to reduce the ITR at the soft/hard material interface. Here, we report a design of an elastomer composite consisting of a polyurethane-thioctic acid copolymer and microscale spherical aluminum, which exhibits both high phonon spectra match and high adhesion energy (>1000 J/m2) with hard materials, thus leading to a low ITR of 0.03 mm2·K/W. We further develop a quantitative physically based model connecting the adhesion energy and ITR, revealing the key role the adhesion energy plays. This work serves to engineer the ITR at the soft/hard material interface from the aspect of adhesion energy, which will prompt a paradigm shift in the development of interface science.

Man Zhou

Papers

Multilayer in-plane graphene/hexagonal boron nitride heterostructures: Insights into the interfacial thermal transport properties

Phonon transport in antisite-substituted hexagonal boron nitride nanosheets: A molecular dynamics study

Interfacial Thermal Conductance of BP/MoS2 van der Waals Heterostructures: an Insight from the Phonon Transport

Interfacial Thermal Conductance and Thermal Rectification Across In-Plane Graphene/h-BN Heterostructures With Different Bonding Types

Can Adhesion Energy Optimize Interface Thermal Resistance at a Soft/Hard Material Interface?