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Pakornchote T.,Chulalongkorn University | Bovornratanaraks T.,Chulalongkorn University | Vannarat S.,Large Scale Simulation Research Laboratory | Pinsook U.,Chulalongkorn University
Solid State Communications | Year: 2016

We investigate the wave-like arrangements of H atoms around metal plane (Hm) in the ScH3 hcp phase by using the ab-initio method. We found that only P63/mmc, P3¯c1, P63cm and P63 phases are energetically favorable. The wave-like arrangement allows the off-site symmetry positions of the H atoms, and leads to substantial changes in the pair distribution between Sc and H atoms which are associating with the changes in the electronic structure in such a way that the total energy is lowering. The symmetry breaking from P63mmc is also responsible for the band gap opening. In the P63 structure, the calculated band gap is 0.823 eV and 1.223 eV using GGA and sX-LDA functionals, respectively. This band gap can be compared with 1.7 eV derived from the optical measurement and 1.55 eV from the HSE06 calculation. Thus, the broken symmetry structures can be viewed as Peierls distortion of the P63/mmc structure. Furthermore, we found that only the P63 structure is dynamically stable, unlike YH3 where the P63cm structure is also stable. The stability of P63 comes from sufficiently strong interactions between two neighboring H atoms at their off-site symmetry positions, i.e. near the metal plane and near the tetragonal site. The P63 phonon density of states is in good agreement with the data from the neutron experiment. © 2015 Elsevier Ltd.


Prueksaaroon S.,King Mongkuts University of Technology Bangkok | Prueksaaroon S.,Large Scale Simulation Research Laboratory | Varavithya V.,King Mongkuts University of Technology Bangkok
International Journal of Advancements in Computing Technology | Year: 2012

Computer clusters have become a main stream of high performance computing platforms. To harvest these high performance systems, cluster operating environment has pressed on an additional abstraction using virtualization technology. Specific problem solving environments are isolated at the operating system level where real executions are performed in virtualization domains. Virtualization technology helps not only increasing utilization of computing resources but also reducing configuration workload, administrative cost, application porting, and energy saving. In this work, we investigated an implementation of virtualization cluster. The experimental performance results of the virtualization cluster are presented. We describe a framework to adopt virtualization onto the clusters. The management of virtualization cluster is discussed. The definitions for the operations of virtual clusters are given. Based on these definitions, we proposed the virtual cluster scheduler where the newly introduced provisioning factors and the goodness factor extend flexibility in management of a cluster. The virtual cluster scheduler can be used as a basis of implementing virtual cluster management. The software layers for virtual cluster management are discussed and the job submission workflow is explained. The framework for organizing cluster resources in virtualization environment is described.


Sirisup S.,Large Scale Simulation Research Laboratory | Maleewong M.,Kasetsart University
Modelling and Simulation in Engineering | Year: 2012

The projective integration method based on the Galerkin-free framework with the assistance of proper orthogonal decomposition (POD) is presented in this paper. The present method is applied to simulate two-dimensional incompressible fluid flows past the NACA0012 airfoil problem. The approach consists of using high-accuracy direct numerical simulations over short time intervals, from which POD modes are extracted for approximating the dynamics of the primary variables. The solution is then projected with larger time steps using any standard time integrator, without the need to recompute it from the governing equations. This is called the online projective integration method. The results by the projective integration method are in good agreement with the full scale simulation with less computational needs. We also study the individual function of each POD mode used in the projective integration method. It is found that the first POD mode can capture basic flow behaviors but the overall dynamic is rather inaccurate. The second and the third POD modes assist the first mode by correcting magnitudes and phases of vorticity fields. However, adding the fifth POD mode in the model leads to some incorrect results in phase-shift forms for both drag and lift coefficients. This suggests the optimal number of POD modes to use in the projective integration method. © 2012 Sirod Sirisup and Montri Maleewong.


Pluengphon P.,Huachiew Chalermprakiet University | Bovornratanaraks T.,Chulalongkorn University | Bovornratanaraks T.,center | Vannarat S.,Large Scale Simulation Research Laboratory | And 2 more authors.
Solid State Communications | Year: 2014

Ab initio calculations were performed for investigating the high pressure phases of GaAs up to 200 GPa. By comparing the minimum free energies of structures, we found the thermodynamically stable phases of GaAs under pressure beyond GaAs-III (Imm2) with space groups Pmma and P4/nmm at the pressure range of 88-146 GPa and 146-200 GPa, respectively. For discussing the difference results of GaAs IV and V in previous studies, we found that Pmma and P4/nmm are the lower symmetric phases of P6/mmm and CsCl-like, respectively. For analyzing the Pmma→P4/nmm phase transition, we observed the approximated path and found that the barrier of transformation from Pmma to P4/nmm in direction [110] is 0.035 eV. The graph of density of states shows no energy gap in stable phases at 130 and 160 GPa, indicating that Pmma and P4/nmm are the metallic phases. The contour plots of the electron density difference show some valence electron sharing in Pmma which is higher than in P4/nmm. Moreover, the results of elastic parameters and modulus ratio suggested that the Pmma phase is a ductile material, while the P4/nmm phase is a brittle due to the increasing of shear modulus. © 2014 Elsevier Ltd. All rights reserved.


Kijsipongse E.,Large Scale Simulation Research Laboratory | U-Ruekolan S.,Large Scale Simulation Research Laboratory
2012 9th International Conference on Electrical Engineering/Electronics, Computer, Telecommunications and Information Technology, ECTI-CON 2012 | Year: 2012

In the recent years, high performance computing (HPC) resources has grown up rapidly and diversely. The next generation of HPC platforms is assembled from resources of various types such as multi-core CPUs and GPUs. Thus, the development of a parallel program to fully utilize heterogeneously distributed resources in HPC environment is a challenge. A parallel program should be portable and able to run efficiently on all types of computing resources with the least effort. We combine the advantages of Global Arrays and OpenCL for such the parallel programs. We employ the OpenCL in implementing parallel applications at fine-grain level so that they can execute across heterogeneous platforms. At coarse grain level, we utilize the Global Arrays for efficient data communication between computing resources in terms of virtually shared memory. In addition, we also propose a load balancing technique based on the task pool model for hybrid OpenCL/Global Arrays applications on heterogeneous platforms to improve the performance of the applications. © 2012 IEEE.

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