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

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Studies in Surface Science and Catalysis

Cu-MOF derived Cu/Cu2O/C nanocomposites for the efficient thermal decomposition of ammonium perchlorate

An interesting Cu-Co/GO composite with special high organic content was accidentally fabricated for the first time via a one-pot solvothermal method in the mixed solvent of isopropanol and glycerol. The Cu-Co/GO composite was calcined separately in three different atmospheres (air, nitrogen, and argon) and further investigated by a series of characterization techniques. The results indicate that the spinel phase nano-CuCo2O4 composite, nanometal oxides (CuO and CoO), and nanometal mixture of Cu and Co were unexpectedly formed after calcination in air, N2, and Ar atmospheres, respectively, and the possible reaction mechanism was discussed. The specific mass losses of the Cu-Co/GO composite calcined in air, N2, and Ar atmospheres were 28.14 %, 21.68 %, and 23.76 %, respectively. The catalytic decomposition performances of the as-prepared samples for cyclotrimethylenetrinitramine (RDX) and the mixture of nitrocellulose (NC) and RDX (NC + RDX) were investigated and compared via DSC method, and the results demonstrate that Cu-Co/GO composites obviously decrease the thermal decomposition temperature of RDX from 242.3 to 236.5 (before calcination), 238.6 (air), 235.8 (N2), and 228.6 °C (Ar), respectively. Cu-Co/GO(Ar) composite exhibits the best catalytic decomposition performance among all samples, which makes the decomposition temperature of RDX and NC + RDX decrease by 13.7 and 4.9 °C and the apparent activation energy of decomposition for RDX decrease by 110.1 kJ/mol. The enhanced catalytic performance of Cu-Co/GO(Ar) composite could be attributed to the smaller particle size, better crystallinity, and specific well-dispersed metal atoms, whereas the Cu-Co/GO(air) composite after air calcination presents a bad catalytic performance due to the removal of GO.

Unusual Cu-Co/GO Composite with Special High Organic Content Synthesized by an in Situ Self-Assembly Approach: Pyrolysis and Catalytic Decomposition on Energetic Materials.

On the Selection of Boundary Conditions for Droplet Evaporation and Condensation at high Pressure and Temperature Conditions from interfacial Transport Resistivities

Burn rate enhancement of ammonium perchlorate–nitrocellulose composite solid propellant using copper oxide–graphene foam micro-structures

Molecular investigation of sub-to-supercritical transition of hydrocarbon mixtures: Multi-component effect

Vapor-liquid interfacial properties of n-heptane/nitrogen at various temperatures and pressures in the ranges of 270-648 K and 10-60 bar were investigated using molecular dynamics (MD) simulations. Additionally, density gradient theory (DGT) was used to predict the binary system interface for qualitative comparison purposes. Results show that surface tension decreases with the increases in both temperature and pressure, but the rate of decrease against the latter is smaller. The interface thickness, which is of the order of several nanometers, was also shown to have a much stronger dependence on temperature and almost invariant with respect to pressure. MD also reveals the phenomenon of nitrogen enrichment in the outer interfacial region at low subcritical temperatures. A sensitivity analysis of influence parameters on DGT results revealed that surface tension values are a stronger function of n-heptane influence parameter and almost invariant with respect to nitrogen influence parameter. The velocity distribution function (VDF) shows that the molecules in and away from the interface follow the Maxwellian distribution of kinetic theory at subcritical conditions. The VDF of the velocity component normal to the interface of the evaporated n-heptane molecules adjacent to the interface exhibits a deviation from the Maxwellian distribution. The VDF of all three components of velocity of n-heptane molecules at supercritical conditions exhibits a departure from the Maxwellian distribution as well.

Suman Chakraborty

Papers

Burn rate enhancement of ammonium perchlorate–nitrocellulose composite solid propellant using copper oxide–graphene foam micro-structures

Molecular investigation of sub-to-supercritical transition of hydrocarbon mixtures: Multi-component effect

Molecular Dynamics Simulations of Vapor-Liquid Interface Properties of n-Heptane/Nitrogen at Subcritical and Transcritical Conditions.

Molecular Dynamics Investigation of Sub-to-supercritical Transition of n-Alkane Fuel Mixtures in Nitrogen

Effect of CuO-Graphene Foam (GF) Micro-structures on the Decomposition of AP-NC Composite Solid Propellant