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

The Theory of Matrices. By F R. Gantmacher. Two volumes, pp. 374 and 276. 1959. (Translated from the Russian by K. A. Hirsch; Chelsea Publishing Company, New York)

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The Science And Engineering Of Materials

Thank you very much for downloading introduction to polymers. As you may know, people have look hundreds times for their favorite readings like this introduction to polymers, but end up in infectious downloads. Rather than reading a good book with a cup of coffee in the afternoon, instead they are facing with some infectious virus inside their desktop computer. introduction to polymers is available in our digital library an online access to it is set as public so you can get it instantly. Our digital library saves in multiple countries, allowing you to get the most less latency time to download any of our books like this one. Kindly say, the introduction to polymers is universally compatible with any devices to read.

Introduction To Polymers

The bond lengths and bond angles of orthorhombic black phosphorus have been determined as a function of hydrostatic pressures to 26.6(5) kbar using time‐of‐flight neutron powder diffraction. We show that the markedly anisotropic compression reported previously results from a large pressure‐induced shortening of the van der Waals bonds separating layers of atoms combined with a shear motion within the layers. Covalently bonded chains of atoms along the a direction remain very rigid. The average effective linear compressibility for van der Waals bonds is 1.48(9) ×10−3 kbar−1 while the average effective linear compressibility for covalent bonds is an order of magnitude smaller, 2.6(8) ×10−4 kbar−1.

Effect of pressure on bonding in black phosphorus Locality: synthetic Sample: at P = 1.02 GPa Note: pressures calculated from the measured unit cell volume

Ab initio thermodynamics of zirconium hydrides and deuterides

Semi-empirical atomistic study of point defect properties in BCC transition metals

We present a theoretical model to calculate the flexural rigidity of nanowires from three-dimensional elasticity theory that incorporates the effects of surface stress and surface elasticity. The unique features of the model are that it incorporates, through the second moment, the heterogeneous nature of elasticity across the nanowire cross section, and that it accounts for transverse surface-stress-induced relaxation strains. The model is validated by comparison to benchmark atomistic calculations, existing one-dimensional surface elasticity theories based on the Young–Laplace equation, and also three-dimensional surface elasticity theories that assume homogeneous elastic properties across the nanowire cross section via three examples: surface-stress-induced axial relaxation, resonant properties of unstrained, strained and top-down nanowires, and buckling of nanowires. It is clearly demonstrated that the one-dimensional Young–Laplace models lead to errors of varying degrees for all of the boundary value problems considered because they do not account for transverse surface stress effects, and it is also shown that the Young–Laplace model results from a specific approximation of the proposed formulation. The three-dimensional surface elasticity model of Dingreville et al. (2005) is found to be more accurate than the Young–Laplace model, though both lose accuracy for ultrasmall ( 5 nm diameter) nanowires where the heterogeneous nature of the cross section elasticity becomes important. Overall, the present work demonstrates that continuum mechanics can be utilized to study the elastic and mechanical behavior and properties of ultrasmall nanowires if surface elastic contributions to the heterogeneous flexural rigidity are accounted for.

On the importance of surface elastic contributions to the flexural rigidity of nanowires

In this work, resonant and elastic properties of single crystal gold nanowires have been studied through classical molecular dynamics simulations. The considered nanowires have perfect square cross sections and are oriented with the [100] direction along the wire axis and with {100} side surfaces. Three different sizes were simulated; 4.08×4.08 nm2, 5.71×5.71 nm2, and 7.34×7.34 nm2 cross sectional dimensions, with the respective unrelaxed lengths 49.0 nm, 68.5 nm, and 88.1 nm and the simulations were performed at two different temperatures, 4.2 K and 300 K. Tensile simulations reveal, that the stiffness decreases with decreasing size, and that the size dependence for nanowires at 4.2 K can be accurately described using the concept of surface energy. Comparing results from the resonant simulations reveals that the fundamental eigenfrequency is in good agreement with predictions from Bernoulli–Euler continuum beam theory when the size dependence of the stiffness is taken into account. The eigenfrequencies of the first and second excited modes turn out to be low in comparison with analytical Bernoulli–Euler continuum calculations.

Transverse resonant properties of strained gold nanowires

In this paper, we report the results of a systematic study of the elastic properties of nanosized single-crystal wires and beams of bcc iron. Both tensile and bending stiffnesses have been determined employing molecular statics simulations for specimens of different sizes and three different crystallographic orientations. We also analyze the influence of circular cross sections and rounded edges compared to square cross sections with sharp edges for one of the crystallographic orientations. The simulations show that there is a size dependence in Young's modulus and that different crystallographic orientations display different elastic behaviors. There are bands of deviating Young's modulus over the cross sections in the direction 45 degrees from the surfaces emanating from the edges, giving the cross section a heterogeneous character. Rounding the edges, or making the cross section circular, has little influence on the average Young's modulus, but it does influence the distribution over the cross section and, consequently, the aforementioned bands. (Less)

Pär Olsson

Papers

Ab initio thermodynamics of zirconium hydrides and deuterides

Semi-empirical atomistic study of point defect properties in BCC transition metals

On the importance of surface elastic contributions to the flexural rigidity of nanowires

Transverse resonant properties of strained gold nanowires

Atomistic simulations of tensile and bending properties of single-crystal bcc iron nanobeams