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

Note: Times Cited: 875 Reference EPFL-ARTICLE-206025doi:10.1021/cr0501846View record in Web of Science URL: ://WOS:000249839900009 Record created on 2015-03-03, modified on 2017-05-12

Complex Hydrides for Hydrogen Storage

Data Reduction And Error Analysis For The Physical Sciences

From first-principles calculations, we predict that a single ethylene molecule can form a stable complex with two transition metals (TM) such as Ti. The resulting TM-ethylene complex then absorbs up to ten hydrogen molecules, reaching to gravimetric storage capacity of $\ensuremath{\sim}14\text{ }\text{ }\mathrm{wt}\text{ }%$. Dimerization, polymerizations, and incorporation of the TM-ethylene complexes in nanoporous carbon materials are also discussed. Our results are quite remarkable and open a new approach to high-capacity hydrogen-storage materials discovery.

/pdf/transition-metal-ethylene-complexes-as-high-capacity-1kwaaabww7.pdf

Transition Metal-Ethylene Complexes as High-Capacity Hydrogen Storage Media

Based on first-principles plane wave calculations, we showed that Ca adsorbed on graphene can serve as a high-capacity hydrogen storage medium, which can be recycled by operations at room temperature. Ca is chemisorbed by donating part of its $4s$ charge to the empty ${\ensuremath{\pi}}^{\ensuremath{\ast}}$ band of graphene. At the end the adsorbed Ca atom becomes positively charged and the semimetallic graphene changes into a metallic state. While each of the adsorbed Ca atoms forming the $(4\ifmmode\times\else\texttimes\fi{}4)$ pattern on the graphene can absorb up to five ${\text{H}}_{2}$ molecules, hydrogen storage capacity can be increased to $8.4\text{ }\text{wt}\text{ }%$ by adsorbing Ca to both sides of graphene and by increasing the coverage to form the $(2\ifmmode\times\else\texttimes\fi{}2)$ pattern. Clustering of Ca atoms is hindered by the repulsive Coulomb interaction between charged Ca atoms.

/pdf/hydrogen-storage-of-calcium-atoms-adsorbed-on-graphene-first-41jgrgynqp.pdf

Hydrogen storage of calcium atoms adsorbed on graphene: First-principles plane wave calculations

We present a detailed investigation of the transition properties for He-like Al embedded in hot and dense plasma environments. The correlation effect between the bound electrons is treated with the configuration interaction method. Plasma screening on the nucleus is described using the self-consistent-field ion sphere model. Transition energies, transition probabilities and weighted oscillator strengths decrease quickly with the increase of free electron densities, but increase slightly with the electron temperature, and approach those of the uniform electron density ion sphere model at a given average free electron density. The results reported in this work are useful for plasma diagnostics.

Transition energies, transition probabilities and weighted oscillator strengths of He-like Al in hot and dense plasmas

The Saturn-like charge-transfer complex Li4&B36, which was recently predicted with extensive first-principles theory calculations, were studied as a candidate for hydrogen storage material in the present work. The bonding characters of Li-B, B-B and Li-H2 bonds were revealed by the quantum theory of atoms in molecules (QTAIM). Each Li atom in Li4&B36 cluster can bind six H2 molecules at most, which results into the gravimetric density of 10.4%. The adsorption energies of H2 molecules on Li4&B36 cluster are predicted in the range of 0.08-0.14 eV at the wB97x level of theory.

/pdf/hydrogen-storage-of-li-4-b-36-cluster-1rm6buokqo.pdf

Hydrogen storage of Li 4 &B 36 cluster

Li-decorated B2O as potential candidates for hydrogen storage: A DFT simulations study

Results from multiconfiguration Dirac–Hartree–Fock (MCDHF) and relativistic configuration interaction (RCI) calculations are presented for the n¼ 3t on 0 ¼3 transitions in the Mg isoelectronic sequence. The calculated values for the lowest 35 levels including core– valence correlation are found to be similar and to compare very well with other theoretical and experimental values. The Breit interaction and leading quantum electrodynamic effects are included as perturbations. The calculations can provide useful data for the experimental study of determining the fine structure levels in future work.

Accurate multiconfiguration Dirac–Hartree–Fock calculations of transition probabilities for magnesium-like ions

The structural, elastic, and electronic properties of a series of lanthanide hexaborides (LnB6) have been investigated by performing ab initio calculations based on the density functional theory using the Vienna ab initio simulation package. The calculated lattice and elastic constants of LnB6 are in good agreement with the available experimental data and other theoretical results. The polycrystalline Young's modulus, shear modulus, the ratio of bulk to shear modulus B/G, Poisson's ratios, Zener anisotropy factors, as well as the Debye temperature are calculated, and all of the properties display some regularity with increasing atomic number of lanthanide atoms, whereas anomalies are observed for EuB6 and YbB6. In addition, detailed electronic structure calculations are carried out to shed light on the peculiar elastic properties of LnB6. The total density of states demonstrates the existence of a pseudogap and indicates lower structure stability of EuB6 and YbB6 compared with others.

Gang Jiang

Papers

Transition energies, transition probabilities and weighted oscillator strengths of He-like Al in hot and dense plasmas

Hydrogen storage of Li 4 &B 36 cluster

Li-decorated B2O as potential candidates for hydrogen storage: A DFT simulations study

Accurate multiconfiguration Dirac–Hartree–Fock calculations of transition probabilities for magnesium-like ions

Elastic properties and electronic structures of lanthanide hexaborides