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

In recent years, due to its unparalleled advantages, the biomimetic and bioinspired synthesis of nanomaterials/nanostructures has drawn increasing interest and attention. Generally, biomimetic synthesis can be conducted either by mimicking the functions of natural materials/structures or by mimicking the biological processes that organisms employ to produce substances or materials. Biomimetic synthesis is therefore divided here into "functional biomimetic synthesis" and "process biomimetic synthesis". Process biomimetic synthesis is the focus of this review. First, the above two terms are defined and their relationship is discussed. Next different levels of biological processes that can be used for process biomimetic synthesis are compiled. Then the current progress of process biomimetic synthesis is systematically summarized and reviewed from the following five perspectives: i) elementary biomimetic system via biomass templates, ii) high-level biomimetic system via soft/hard-combined films, iii) intelligent biomimetic systems via liquid membranes, iv) living-organism biomimetic systems, and v) macromolecular bioinspired systems. Moreover, for these five biomimetic systems, the synthesis procedures, basic principles, and relationships are discussed, and the challenges that are encountered and directions for further development are considered.

Biomimetic and Bioinspired Synthesis of Nanomaterials/Nanostructures.

Radiation damage in nanostructured materials

Ion beam induced surface and interface engineering

We review oxygen K-edge X-ray absorption spectra of both molecules and solids. We start with an overview of the main experimental aspects of oxygen K-edge X-ray absorption measurements including X-ray sources, monochromators, and detection schemes. Many recent oxygen K-edge studies combine X-ray absorption with time and spatially resolved measurements and/or operando conditions. The main theoretical and conceptual approximations for the simulation of oxygen K-edges are discussed in the Theory section. We subsequently discuss oxygen atoms and ions, binary molecules, water, and larger molecules containing oxygen, including biomolecular systems. The largest part of the review deals with the experimental results for solid oxides, starting from s- and p-electron oxides. Examples of theoretical simulations for these oxides are introduced in order to show how accurate a DFT description can be in the case of s and p electron overlap. We discuss the general analysis of the 3d transition metal oxides including discussions of the crystal field effect and the effects and trends in oxidation state and covalency. In addition to the general concepts, we give a systematic overview of the oxygen K-edges element by element, for the s-, p-, d-, and f-electron systems.

Oxygen K-edge X-ray Absorption Spectra

Effect of Ti and Cr on dispersion, structure and composition of oxide nano-particles in model ODS alloys

This paper presents the joint effect of strain- and doping-induced band gap change in Sn1−xMnxO (0 ≤ x ≤ 0.05) nanoparticles. In addition, an effort was made to understand the effect of Mn doping on the structural and optical properties of SnO2. X-ray diffraction analysis showed a tetragonal structure and the unit cell volume decreased slightly with Mn4+ content. The Mn:SnO2 are spherical shaped particles with a size ranging from 7.7 to 13.8 nm as calculated by transmission electron microscopy, Scherrer's formula and Willamson–Hall plot. X-ray photoelectron spectroscopy showed clear evidence for tetragonal coordinated high-spin Mn4+ ions occupying the lattice sites of Sn4+ in the SnO2 host. Electron energy loss spectroscopy further confirmed composition and oxidation states of Sn4+ and Mn4+ ions. Manganese doping increased the band gap of SnO2 from 4 eV to 4.40 eV with Mn4+ concentration. Variation in band gap energy was attributed to the increasing lattice strain with Mn content and the charge transfer transitions between Mn4+ ions and conduction/valence bands of SnO2. Three photoluminescence emission bands observed at 320, 360 and 380 nm, when excited at 250 nm, proved Mn:SnO2 to exhibit good optical emission and to have potential application in nanoscale optoelectronic devices.

https://www.rsc.org/suppdata/ra/c3/c3ra46378h/c3ra46378h.pdf

Influence of manganese ions in the band gap of tin oxide nanoparticles: structure, microstructure and optical studies

We report, for the first time, the luminescence property of the hydroxyl group surface functionalized quantum dots (QDs) and nanoparticles (NPs) of SnO2 using low energy excitations of 2.54 eV (488 nm) and 2.42 eV (514.5 nm). This luminescence is in addition to generally observed luminescence from ‘O’ defects. The as-prepared SnO2 QDs are annealed at different temperatures under ambient conditions to create NPs with varying sizes. Subsequently, the average size of the NPs is calculated from the acoustic vibrations observed at low frequencies in the Raman spectra and by the transmission electron microscopy measurements. Detailed photoluminescence studies with 3.815 eV (325 nm) excitation reveal the nature of in-plane and bridging ‘O’ vacancies as well as adsorption and desorption occurring at different annealing temperatures. X-ray photoelectron spectroscopy studies also support this observation. The defect level related to the surface –OH functional groups shows a broad luminescence peak at around 1.96 eV in SnO2 NPs which is elaborated using temperature dependent studies.

Photoluminescence of oxygen vacancies and hydroxyl group surface functionalized SnO2 nanoparticles

Methane (CH4) gas sensing properties of novel vanadium dioxide (VO2) nanostructured films is reported for the first time. The single phase nanostructures are synthesized by pulsed dc-magnetron sputtering of V target followed by oxidation in O2 atmosphere at 550 °C. The partial pressure of O2 is controlled to obtain stoichiometric VO2 with the samples showing rutile monoclinic crystalline symmetry and regions of rod shaped nano-architectures. These nanostructured films exhibit a reversible semiconductor to metal transition in the temperature range of 60–70 °C. Gas sensing experiments are carried out in the temperature span from 25 °C to 200 °C in presence of CH4. These experiments reveal that the films respond very well at temperatures as low as 50 °C, in the semiconducting state.

Novel single phase vanadium dioxide nanostructured films for methane sensing near room temperature

We report, for the first time, the luminescence property of the hydroxyl group surface functionalized quantum dots (QDs) and nanoparticles (NPs) of SnO_2 using low energy excitations of 2.54 eV (488 nm) and 2.42 eV (514.5 nm). This luminescence is in addition to generally observed luminescence from 'O' defects. The as-prepared SnO_2 quantum dots (QDs) are annealed at different temperatures in ambient conditions to create varied NPs in size. Subsequently, average size of the NPs is calculated from the acoustic vibrations observed at low frequencies in the Raman spectra and by the transmission electron microscopic measurements. Detailed photoluminescence studies with 3.815 eV (325 nm) excitation reveal the nature of in-plane and bridging 'O' vacancies as well as adsorption and desorption occurred at different annealing temperatures. X-ray photoelectron spectroscopy studies also support this observation. Defect level related to the surface -OH functional groups shows a broad luminescence peak around 1.96 eV in SnO_2 NPs which is elaborated with the help of temperature dependent studies.

S. Amirthapandian

Papers

Effect of Ti and Cr on dispersion, structure and composition of oxide nano-particles in model ODS alloys

Influence of manganese ions in the band gap of tin oxide nanoparticles: structure, microstructure and optical studies

Photoluminescence of oxygen vacancies and hydroxyl group surface functionalized SnO2 nanoparticles

Novel single phase vanadium dioxide nanostructured films for methane sensing near room temperature

Photoluminescence of oxygen vacancies and hydroxyl group surface functionalized SnO_2 nanoparticles