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The composite of epoxy polymers and α-alumina fillers is used as a heat dissipation material. The fillers often agglomerate with nanometer-depth polymers sandwiched in between. We address theoretically the effective thermal conductivity of such a filler-polymer-filler system. The non-equilibrium molecular dynamics simulation is performed to obtain the effective thermal conductivity of the system, in which bisphenol-A (bisA) epoxy polymer sub-system with depth 14–70 A is inserted between two α-alumina slabs. Effects of surface-coupling (SC) agent are also investigated by adding model molecules to the polymer sub-system. For smaller polymer-depth cases, the effective thermal conductivity is determined essentially by the interfacial thermal conductance that relates to the temperature-gaps at the interfaces. We find for the interfacial thermal conductance that: (i) it is decreased by decreasing the polymer depth toward the chain length of a single bisA molecule, and (ii) it is increased by adding the SC molecules to the polymer sub-system. Combining separate simulation analyses, we show that the (i) results from effectively weakened interaction between a bisA molecule and two α-alumina slabs due to the orientation constraint on the bisA molecule by the slabs. Reasons of the (ii) are enhancement of the following three quantities by addition of the SC molecules: the phonon population of the bisA molecules at those frequencies corresponding to that of acoustic phonons of α-alumina, the phonon transmission coefficient from the α-alumina slab to the polymer sub-system for the transverse acoustic phonon, and the group velocity of the transverse acoustic phonon in the polymer sub-system.

Molecular dynamics simulation has been performed to investigate the effects of irradiated helium atoms in tungsten on the bubble nucleation and the dislocation loop formation. Simulation results clearly show that helium atoms in tungsten tend to migrate as isolated interstitials at high temperatures and to be absorbed to existing tungsten-vacancies or defects such as bubbles or dislocations. Tungsten self-interstitial atoms pushed out from the helium bubble tend to stay in the vicinity of the bubble and, then form a dislocation loop when the number of the atoms exceed the threshold. Since the bubbles and dislocation loops cause further nucleation of bubbles, there appears a helium bubble array along 〈 1 1 1 〉 direction. The bubble growth rate within this self induced bubble growth mechanism will be much faster than that of existing growth model. The growth model needs to be reformulated by taking the self-induced effects into account.

Publisher Summary This chapter discusses the scalable multiresolution algorithmsfor Ccassical and quantum molecular dynamics simulations of nanosystems. The chapter illustrates that modern MD simulations of materials stimulates 864 argon atoms on a CDC 3600 computer. Assuming a simple exponential growth, the number of atoms that can be simulated in classical MD simulations has doubled every 19 months to reach 6.44 billion atoms in 2000. The chapter explores petaflops computers which can maintain the growth rates in these “MD Moore's Laws,” and it is able to perform 10 12 -atom classical and 10 7 -atom quantum MD simulations on such computers. Multi resolution approaches described in this chapter, combined with cache-conscious techniques, is essential to achieve scalability on petaflop architectures. In addition, atomistic simulations have reached a scale such that they must be performed in a Meta computing environment of a grid o geographically-distributed multiple supercomputers. Such grid-computing efforts are also underway. Another promising direction toward achieving scalability is the development multiscale simulations schemes that seamlessly combine QM and MD calculations with the continuum mechanics calculation based on the linear elasticity and the finite element method in a single simulation program

Screening potentials between ions in dense C-O mixtures appropriate to white-dwarf interiors are analyzed by Monte Carlo simulation method, both in a fluid and in a bcc-crystalline state. Criteria for the validity of a classical approximation in the screening potential are derived; it is shown that the classical approximation applies only in a fluid state for a C matter. Enhancement rate of nuclear reactions in a dense C-O fluid is calculated.

We perform Monte Carlo simulation study for short-range correlations between itinerant hydrogen, interacting mutually via electron-screened repulsive forces, in periodic and aperiodic (due to defects) lattice fields of metal hydrides. We find that the screening potentials and the resultant fusion rates depend extremely sensitively on microscopic details in the lattice fields, corroborating qualitatively the varied results in recent “cold fusion” experiments.

We report the results of the first microscopic study by Monte Carlo (MC) simulation ( N = 1458) of how the particle correlations and bond-orientational orders develop in supercooled one-component plasmas (OCP's) at the freezing transitions. Starting with an equilibrated fluid state at Γ = 160, where Γ is the inverse temperature in units of the average Coulomb energy, we apply gradual quenches stepwise until Γ = 200, 300, or 400 is reached. The OCP at Γ = 200 remains in a supercooled fluidlike state. In the quenches to Γ = 300 or 400, we discovered an internal development of particle layers, which acted to expedite subsequent evolution of the OCP into a metastable solid state. The final state is found to be a bcc crystalline state with a small number of intralayer interstitials. The static structure factors calculated at Γ = 160, 200, 300, 400, and 800 are applied for explicit evaluation of the electric and thermal conductivities in dense Fe matter appropriate to the outer crustal material of neutron stars. The screening potentials of the OCP fluids and solids are expressed in parametrized forms, and are used for evaluation of the nuclear reaction rates in dense OCP matter. Dense plasmas more complex than the OCP has been studied by the MC method, two of such examples being dense C-O mixtures in white dwarfs and itinerant hydrogen atoms in metal hydrides.