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

Intermolecular And Surface Forces

Numerical Initial Value Problems in Ordinary Differential Equations

http://nathan.instras.com/documentDB/paper-69.pdf

Porous silicon: a quantum sponge structure for silicon based optoelectronics

Artificial Molecular Rotors

This article describes the advances that have been made over the past ten years on the problem of fracton excitations in fractal structures. The relevant systems to this subject are so numerous that focus is limited to a specific structure, the percolating network. Recent progress has followed three directions: scaling, numerical simulations, and experiment. In a happy coincidence, large-scale computations, especially those involving array processors, have become possible in recent years. Experimental techniques such as light- and neutron-scattering experiments have also been developed. Together, they form the basis for a review article useful as a guide to understanding these developments and for charting future research directions. In addition, new numerical simulation results for the dynamical properties of diluted antiferromagnets are presented and interpreted in terms of scaling arguments. The authors hope this article will bring the major advances and future issues facing this field into clearer focus, and will stimulate further research on the dynamical properties of random systems.

/pdf/dynamical-properties-of-fractal-networks-scaling-numerical-34gns79y2x.pdf

Dynamical properties of fractal networks: Scaling, numerical simulations, and physical realizations

Type-I clathrate compounds have attracted a great deal of interest in connection with the search for efficient thermoelectric materials. These compounds constitute networked cages consisting of nano-scale tetrakaidecahedrons (14 hedrons) and dodecahedrons (12 hedrons), in which the group 1 or 2 elements in the periodic table are encaged as the so-called rattling guest atom. It is remarkable that, though these compounds have crystalline cubic-structure, they exhibit glass-like phonon thermal conductivity over the whole temperature range depending on the states of rattling guest atoms in the tetrakaidecahedron. In addition, these compounds show unusual glass-like specific heats and THz-frequency phonon dynamics, providing a remarkable broad peak almost identical to those observed in topologically disordered amorphous materials or structural glasses, the so-called Boson peak. An efficient thermoelectric effect is realized in compounds showing these glass-like characteristics. This decade, a number of experimental works dealing with type-I clathrate compounds have been published. These are diffraction experiments, thermal and spectroscopic experiments in addition to those based on heat and electronic transport. These form the raw materials for this article based on advances this decade. The subject of this article involves interesting phenomena from the viewpoint of not only physics but also from the view point of the practical problem of elaborating efficient thermoelectric materials. This review presents a survey of a wide range of experimental investigations of type-I clathrate compounds, together with a review of theoretical interpretations of the peculiar thermal and dynamic properties observed in these materials.

/pdf/phonon-glass-electron-crystal-thermoelectric-clathrates-2jojtwpik8.pdf

Phonon-glass electron-crystal thermoelectric clathrates : Experiments and theory

This paper describes the progress that has been made in the past decade in the investigation of the peculiar dynamic properties of vitreous silica (v-SiO2) and related glasses in the terahertz (THz) frequency range. The reason why we focus our attention on v-SiO2 is that it is one of the principal network glasses and exhibits all features typical of glasses. These are the increased inelastic scattering of light and neutrons at THz frequencies, the so-called Boson or Bose peak, as well as unusual thermal properties such as specific heats and thermal conductivities at low temperatures. During the last decade, experimental techniques such as the inelastic scattering of light, neutrons and x-rays have been greatly improved, and these have provided considerable experimental information about the atomic vibrations in v-SiO2 and related glasses in the THz frequency region. In addition, molecular dynamics simulations have proved successful for these complex systems. They form the basis for this perspective on the major advances in this decade from a new and tutorial point of view.

https://subutu-ap.eng.hokudai.ac.jp/nakayama/pdf/Reports_on_Progress_in_Physics_Vol.65_pp.1195-1242(2002).pdf

Boson peak and terahertz frequency dynamics of vitreous silica

We investigate localization properties of electron eigenstates in one-dimensional (1D) systems with long-range correlated diagonal disorder. Numerical studies on the localization length $\ensuremath{\xi}$ of eigenstates demonstrate the existence of the localization-delocalization transition in 1D systems and elucidate nontrivial behavior of $\ensuremath{\xi}$ as a function of the disorder strength. The critical exponent $\ensuremath{\nu}$ for localization length is extracted for various values of parameters characterizing the disorder, revealing that every $\ensuremath{\nu}$ disobeys the Harris criterion $\ensuremath{\nu}g2∕d$.

/pdf/localization-delocalization-transition-in-one-dimensional-191j2qlt4r.pdf

Localization-delocalization transition in one-dimensional electron systems with long-range correlated disorder

1. Introduction.- 2. Fractals.- 3. Percolating Networks as Random Fractals.- 4. Multifractals.- 5. Anomalous Diffusion on Fractal Networks.- 6. Atomic Vibrations of Percolating Networks.- 7. Scaling Arguments for Dynamic Structure Factors.- 8. Spin Waves in Diluted Heisenberg Antiferromagnets.- 9. Anderson Transition.- 10. Multifractals in the Anderson Transition.- Appendices.- A. Multifractality of the HRN Model.- B. Spectral Dimensions for Deterministic Fractals.- B.1 Sierpinski Gasket.- B.2 Mandelbrot-Given Fractal.- C. Diffusion and Dynamics on Networks.- C.1 Atomic Vibrations.- C.2 Spin Waves in Diluted Ferro- and Antiferromagnets.- C.3 Superconducting Networks.- D. Wigner Distributions.- References.

Tsuneyoshi Nakayama

Papers

Dynamical properties of fractal networks: Scaling, numerical simulations, and physical realizations

Phonon-glass electron-crystal thermoelectric clathrates : Experiments and theory

Boson peak and terahertz frequency dynamics of vitreous silica

Localization-delocalization transition in one-dimensional electron systems with long-range correlated disorder

Fractal concepts in condensed matter physics