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

First-principles calculations have evolved from mere aids in explaining and supporting experiments to powerful tools for predicting new materials and their properties. In the first part of this review we describe the state-of-the-art computational methodology for calculating the structure and energetics of point defects and impurities in semiconductors. We will pay particular attention to computational aspects which are unique to defects or impurities, such as how to deal with charge states and how to describe and interpret transition levels. In the second part of the review we will illustrate these capabilities with examples for defects and impurities in nitride semiconductors. Point defects have traditionally been considered to play a major role in wide-band-gap semiconductors, and first-principles calculations have been particularly helpful in elucidating the issues. Specifically, calculations have shown that the unintentional n-type conductivity that has often been observed in as-grown GaN cannot be a...

First-principles calculations for defects and impurities: Applications to III-nitrides

Electric energy security is essential, yet the high cost and limited sources of fossil fuels, in addition to the need to reduce greenhouse gasses emission, have made renewable resources attractive in world energy-based economies. The potential for renewable energy resources is enormous because they can, in principle, exponentially exceed the world׳s energy demand; therefore, these types of resources will have a significant share in the future global energy portfolio, much of which is now concentrating on advancing their pool of renewable energy resources. Accordingly, this paper presents how renewable energy resources are currently being used, scientific developments to improve their use, their future prospects, and their deployment. Additionally, the paper represents the impact of power electronics and smart grid technologies that can enable the proportionate share of renewable energy resources.

Renewable energy resources: Current status, future prospects and their enabling technology

Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼1.9 μm (0.64 eV for InN) to the ultraviolet at ∼0.36 μm (3.4 eV for GaN...

When group-III nitrides go infrared: New properties and perspectives

During the last few years the interest in the indium nitride (InN) semiconductor has been remarkable. There have been significant improvements in the growth of InN films. High quality single crystalline InN film with two-dimensional growth and high growth rate are now routinely obtained. The background carrier concentration and Hall mobility have also improved. Observation of strong photoluminescence near the band edge is reported very recently, leading to conflicts concerning the exact band gap of InN. Attempts have also been made on the deposition of InN based heterostructures for the fabrication of InN based electronic devices. Preliminary evidence of two-dimensional electron gas accumulation in the InN and studies on InN-based field-effect transistor structure are reported. In this article, the work accomplished in the InN research, from its evolution to till now, is reviewed. The In containing alloys or other nitrides (AlGaInN, GaN,AlN) are not discussed here. We mainly concentrate on the growth, characterization, and recent developments in InN research. The most popular growth techniques, metalorganic vapor phase epitaxy and molecular beam epitaxy, are discussed in detail with their recent progress. Important phenomena in the epitaxialgrowth of InN as well as the problems remaining for future study are also discussed.

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Indium nitride (InN): A review on growth, characterization, and properties

Solar cells are a promising renewable and carbon-free electric energy resource to address the fossil-fuel shortage and global warming. Energy conversion efficiencies over 40% have been recently achieved using conventional III–V semiconductor compounds as photovoltaic materials. The revision of InN bandgap to a much narrower value has extended the fundamental bandgap of the group III-nitride alloy system over a wider spectral region (from 0.64 eV for InN to 3.4 eV for GaN or 6.2 eV for AlN), raising the possibility of a variety of new applications. The tunable bandgap, predicted high radiation resistance, and strong absorption coefficient of the In $_x$ Ga $_{ 1-x}$ N material system are promising for high-efficiency photovoltaic systems. During the past few years, the interest in In $_x$ Ga $_{ 1-x}$ N solar cells has been remarkable. The development of high-performance solar cells using In $_x$ Ga $_{1-x}$ N materials is one of the most important goals when compared with the existing solar cells using Si and other III–V materials. Significant efforts and progress have been made toward this goal, while great opportunities and grand challenges coexist. In this paper, we present a review on the present state of the art of In $_x$ Ga $_{1-x}$ N-based solar cells. The most important challenges toward the high-efficiency In $_x$ Ga $_{ 1-x}$ N-based solar cells are discussed in the context of the recent results.

InGaN Solar Cells: Present State of the Art and Important Challenges

Single crystalline InN films with an absorption edge between 0.7 and 2 eV have been grown using a variety of different techniques, including conventional metal-organic vapor-phase epitaxy (MOVPE), ArF-laser assisted MOVPE (la-MOVPE), and plasma-assisted molecular-beam epitaxy (pa-MBE). Analysis of samples grown using different methods has led to important evidence for determining the actual band gap energy of InN. In an effort to find the origin of the change in absorption edge, this evaluation was focused on the la-MOVPE of InN. This deposition technique enables InN film deposition over a wide range of growth temperatures, ranging from room temperature to a very high temperature (700 °C). Characterization of InN films grown over a wide range of temperatures strongly suggests that oxygen contamination leads to a larger band gap absorption energy value than the actual value, even in the case of single crystalline films. In films grown at low temperatures, oxygen appeared to form an alloy, resulting in a la...

Single-crystalline InN films with an absorption edge between 0.7 and 2 eV grown using different techniques and evidence of the actual band gap energy

Recently, two-dimensional silicon carbide (2D-SiC) has attracted considerable interest due to its exotic electronic and optical properties. Here, we explore the thermal properties of 2D-SiC using reverse non-equilibrium molecular dynamics simulation. At room temperature, a thermal conductivity of ∼313 W mK-1 is obtained for 2D-SiC which is one order higher than that of silicene. Above room temperature, the thermal conductivity deviates the normal 1/T law and shows an anomalous slowly decreasing behavior. To elucidate the variation of thermal conductivity, the phonon modes at different length and temperature are quantified using Fourier transform of the velocity auto-correlation of atoms. The calculated phonon density of states at high temperature shows a shrinking and softening of the peaks, which induces the anomaly in the thermal conductivity. On the other hand, quantum corrections are applied to avoid the freezing effects of phonon modes on the thermal conductivity at low temperature. In addition, the effect of potential on the thermal conductivity calculation is also studied by employing original and optimized Tersoff potentials. These findings provide a means for better understating as well as designing the efficient thermal management of 2D-SiC based electronics and optoelectronics in near future.

https://iopscience.iop.org/article/10.1088/1361-6528/ab3697/pdf

Ashraful G. Bhuiyan

Papers

Indium nitride (InN): A review on growth, characterization, and properties

InGaN Solar Cells: Present State of the Art and Important Challenges

Single-crystalline InN films with an absorption edge between 0.7 and 2 eV grown using different techniques and evidence of the actual band gap energy

Anomalous temperature dependent thermal conductivity of two-dimensional silicon carbide.

Anisotropic mechanical behavior of two dimensional silicon carbide: effect of temperature and vacancy defects