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

Reduced anharmonic phonon scattering cross-section slows the decrease of thermal conductivity with temperature

Vacancy, interstitial, and Frenkel pair effects on the tensile strength of α − Zr are studied by molecular dynamics simulations. The uni-axial tensile load is along [0001] direction of the α − Zr samples. The yield stresses and the corresponding yield strains decrease with the increase of the defect concentration for the three types of point defects studied. With the same defect concentration, interstitials decrease the tensile strength the most seriously compared with the vacancies and Frenkel pairs. Interstitial clusters form dislocation loops which decrease the uni-axial tensile strength.

Point defect effects on tensile strength of α−zirconium studied by molecular dynamics simulations

A first principles investigation of the hydrogen-strain synergy on the formation and phase transition of hydrides in zirconium

Nanolayered metallic alloys are promising materials for nuclear applications thanks to their resistance to radiation damage. Here, we investigate the effect of ion (C, Si, and Cu) irradiation at room temperature with different fluences into sputtered Zr/Nb metallic multilayer films with periods 27 nm (thin) and 96 nm (thick). After irradiation, while a high strain in the entire thin nanoscale metallic multilayer (NMM) is observed, a quite small strain in the entire thick NMM is established. This difference is further analyzed by a semianalytical model, and the reasons behind it are revealed, which are also validated by local strain mapping. Both methods show that within a thick layer, two opposite distortions occur, making the overall strain small, whereas in a thin layer, all the atomic planes are affected by the interface and are subjected to only a single type of distortion (Nb─tension and Zr─compression). In both thin and thick NMMs, with increasing damage, the strain around the interface increases, resulting in a release of the elastic energy at the interface (decrease in the lattice mismatch), and the radiation-induced transition of the Zr/Nb interfaces from incoherent to partially coherent occurs. Density functional theory simulations decipher that the inequality of point defect diffusion flux from the inner to the interface-affected region is responsible for the presence of opposite distortions within a layer. Technologically, based on this work, we estimated that Zr/Nb55 with thicknesses around Zr = 24 nm and Nb = 31 nm is the most promising multilayer system with the high radiation damage resistance and minimum swelling for nuclear applications.

Interface-Driven Strain in Heavy Ion-Irradiated Zr/Nb Nanoscale Metallic Multilayers: Validation of Distortion Modeling via Local Strain Mapping.

Effects of vacancies on the mechanical properties of zirconium: An ab initio investigation

It is well known that the irradiation-induced defects strongly influence the mechanical properties of zirconium (Zr) or its alloys in nuclear reactors. However, how the point defect changes the mechanical properties has been rarely studied. Here, we systematically investigated the effect of vacancies on the mechanical properties of alpha-Zr based on density functional theory (DFT). Both uniformly distributed vacancies and vacancy clusters were considered. Our results reveal that the existence of vacancy will reduce the bulk modulus, while enhance the shear and Young's moduli. Based on these moduli, the ductility and hardness were further calculated. With the introduction of vacancy, the ductility decreases, but the hardness increases. However, when the vacancy concentration is larger than a critical value, a rise in the ductility and a reduction in the hardness occur, which indicates the degeneration of the material. Moreover, it was found that the vacancies lead to a more isotropic distribution of Young's modulus in 3D space. To further investigate how the clustering of vacancies influences the mechanical properties, the most stable configurations of di- and trivacancy clusters have been predicted, which correspond to the most compact distribution of vacancies. Compared with the uniform distribution of vacancies, clustering of vacancies will strengthen the above changes of elastic moduli, ductility and hardness. Our results indicate that the increase of the vacancy concentration may be the basic cause for the changes of the mechanical properties under irradiation, while the formation of vacancy clusters intensifies these changes.

Effect of vacancies on the mechanical properties of zirconium: An ab initio investigation

Effect of Xe bubbles on the thermal conductivity of UO2: Mechanisms and model establishment

The invention relates to an atomic structure analysis method and a modeling method of a surface or interface atomic structure, in particular to an analysis method for a local lattice point environmentand a local atomic environment of a low-symmetry or asymmetric atomic structure, and a modeling and analysis method for a surface or interface atomic structure of a disordered solid solution materialby utilizing the analysis method. The structure analysis method is good in universality, and is not only suitable for crystal structure analysis, but also suitable for amorphous structure analysis; on the basis, the modeling method for the surface structure of the novel disordered solid solution material is realized by combining a similar atomic environment (SAE) method, the size of modeling unitcells is flexible and adjustable, and surface segregation can be treated.

Atomic structure analysis method and modeling method of surface or interface atomic structure

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Effects of vacancies on the mechanical properties of zirconium: An ab initio investigation

Effect of vacancies on the mechanical properties of zirconium: An ab initio investigation

Effect of Xe bubbles on the thermal conductivity of UO2: Mechanisms and model establishment

Atomic structure analysis method and modeling method of surface or interface atomic structure