1,721,018 research outputs found
A SOA-based model for the integrated provisioning of cloud and grid resources
Full text linkIn the last years, the availability and models of use of networked computing resources within reach
of e-Science are rapidly changing and see the coexistence of many disparate paradigms: high
performance computing, grid and recently cloud. Unfortunately, none of these paradigms is
recognized as the ultimate solution, and a convergence of them all should be pursued. At the same
time, recent works have proposed a number of models and tools to address the growing needs and
expectations in the field of e-Science. In particular, they have shown the advantages and the
feasibility of modeling e-Science environments and infrastructures according to the Service-
Oriented Architecture.
In this paper we suggest a model to promote the convergence and the integration of the different
computing paradigms and infrastructures for the dynamic on-demand provisioning of resources
from multiple providers as a cohesive aggregate, leveraging the Service-Oriented Architecture. In
addition, we propose a design aimed at endorsing a flexible, modular, workflow-based computing
model for e-Science.
The model is supplemented by a working prototype implementation together with a case study in
the applicative domain of bio-informatics, which are used to validate the presented approach and to
to carry out some performance and scalability measurements
Resource provisioning for e-Science environments
No full textRecent works have proposed a number of models and tools to address the growing needs
and expectations in the field of e-Science. At the same time, the availability and models of
use of networked computing resources needed by e-Science are rapidly changing and see
the coexistence of many disparate paradigms: high performance computing, grid and
recently cloud, which brings very promising expectations due to its high flexibility. In this
paper we suggest a model to promote the convergence and the integration of different
computing paradigms and infrastructures for the dynamic on-demand provisioning of the
resources needed by e-Science environments, leveraging the Service-Oriented
Architecture model. In addition, its design aims at endorsing a flexible, modular,
workflow-based collaborative environment for e-Science. A working implementation used
to validate the proposed approach is described together with some performance tests
DFT-LDA Pseudopotentials in Quantum Monte Carlo
No full textWe investigate the portability of standard norm-conserving pseudopotentials outside the density functional theory-local density approximation (DFT-LDA) framework, i.e., their use and interpretation as electron-ion effective potentials in valence-only diffusion Monte Carlo simulations. While first-principles many-body pseudopotentials are not available in the literature yet, the use of approximate pseudopotentials in quantum Monte Carlo simulations is becoming widespread. Here we attempt a systematic analysis of the portability of norm-conserving pseudopotentials generated within DFT-LDA, focusing on a model many-body system, the two-electron valence-only ion. Our results indicate that the portability is good in most cases, hence the use of pseudopotentials in quantum Monte Carlo simulations is in general a reasonable approximation but suggest that in some cases this approximation may be relevant
Variational Monte Carlo on a parallel architecture: an application to graphite
No full textWe present the parallelization strategy adopted to perform Variational Quantum Monte Carlo calculations on solids on distributed-memory architectures and the issues involved in the development of the parallel programs. Results obtained by the calculation of total electronic energy of graphite using nonlocal pseudopotentials in conjunction with the Variational Monte Carlo approach will be shown
Pseudopotential Portability in the QMC Framework
No full textWe have calculated the binding energies of several two-electron pseudoions using the Diffusion Quantum Monte Carlo method. The comparison between our results and the experiment suggests that HSC pseudopotentials are portable from the original single particle theory (DFT-LDA) to the “exact” many body one. Moreover we are able to evaluate the degree of portability of each effective field
Anomalous relaxations and chemical trends at III-V semiconductor nitride nonpolar surfaces
No full textRelaxations at nonpolar surfaces of semiconductor III-V compounds result from a competition between dehybridization and charge transfer. First-principles calculations for the (110) and (10 (1) over bar 0) faces of zinc-blende and wurtzite AlN, GaN, and InN reveal an anomalous behavior as compared with ordinary III-V semiconductors. Additional calculations for GaAs and ZnO suggest close analogies with the latter. We interpret our results in terms of the larger ionicity (charge asymmetry) and bonding strength (cohesive energy) in the nitrides with respect to other III-V compounds, both essentially due to the strong valence potential and absence of p core states in the lighter anion. The same interpretation applies to Zn IT-VI compounds. [S0165-1829(99)00211-8]
Pseudohamiltonians and Quantum Monte Carlo
No full textA new method is presented for the generation of valence-only local hamiltonians, or pseudohamiltonians, within the DFT-LDA framework. At the moment these promise to be very useful tools to overcome the problem of eliminating the core electrons from many QMC calculations
Structural and electronic properties of AlN, GaN, and InN, and band-offsets at AlN/GaN (0001) and (10-10) interfaces
No full textAb initio local-density-functional calculations are presented for bulk A1N, GaN, and InN in the wurtzite, zincblende, and rocksalt structures. Structural transition pressures and deformation potentials of electronic gaps are investigated. In addition, we study the band offset at the polar (0001) and non-polar (1010) AIN/GaN interfaces. Within AIN-on-GaN epitaxial conditions, we obtain valence-band offset values close to 0.7 eV for both interfaces. From the macroscopic field appearing along the growth direction of the polar interface (tentatively attributed to AIN macroscopic polarization), an estimate of the macroscopic dielectric constant of GaN is extracted. All calculations employed conjugate-gradient total-energy minimizations, ultrasoft pseudopotentials, and plane waves at 25 Ryd cutoff
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