1,961 research outputs found
A spectral scheme for Kohn-Sham density functional theory of clusters
Starting from the observation that one of the most successful methods for
solving the Kohn-Sham equations for periodic systems -- the plane-wave method
-- is a spectral method based on eigenfunction expansion, we formulate a
spectral method designed towards solving the Kohn-Sham equations for clusters.
This allows for efficient calculation of the electronic structure of clusters
(and molecules) with high accuracy and systematic convergence properties
without the need for any artificial periodicity. The basis functions in this
method form a complete orthonormal set and are expressible in terms of
spherical harmonics and spherical Bessel functions. Computation of the occupied
eigenstates of the discretized Kohn-Sham Hamiltonian is carried out using a
combination of preconditioned block eigensolvers and Chebyshev polynomial
filter accelerated subspace iterations. Several algorithmic and computational
aspects of the method, including computation of the electrostatics terms and
parallelization are discussed. We have implemented these methods and algorithms
into an efficient and reliable package called ClusterES (Cluster Electronic
Structure). A variety of benchmark calculations employing local and non-local
pseudopotentials are carried out using our package and the results are compared
to the literature. Convergence properties of the basis set are discussed
through numerical examples. Computations involving large systems that contain
thousands of electrons are demonstrated to highlight the efficacy of our
methodology. The use of our method to study clusters with arbitrary point group
symmetries is briefly discussed.Comment: Manuscript submitted (with revisions) to Journal of Computational
Physic
#49 - Creaton and Analysis of 3-Dimensional Thermal Models
According to the European Commissions, the largest potential saving of energy lies within commercial and residential buildings. A considerable amount of energy loss from buildings is due to heat or infrared radiation. For this reason, we have been collecting infrared data and creating 3-dimensional models of various structures located on the University of North Georgia Dahlonega campus. Images and data were obtained using a drone and a FLIR Pro infrared camera. Using a specialized software, we were able to analyze infrared images. Through the combined use of Agisoft Metashape and many high-resolution infrared images, a 3D model with thermal data can be produced. Through this research, we developed the tools and workflow necessary to analyze the energy loss of these models
Symmetry-Adapted Phonon Analysis of Nanotubes
The characteristics of phonons, i.e. linearized normal modes of vibration,
provide important insights into many aspects of crystals, e.g. stability and
thermodynamics. In this paper, we use the Objective Structures framework to
make concrete analogies between crystalline phonons and normal modes of
vibration in non-crystalline but highly symmetric nanostructures. Our strategy
is to use an intermediate linear transformation from real-space to an
intermediate space in which the Hessian matrix of second derivatives is
block-circulant. The block-circulant nature of the Hessian enables us to then
follow the procedure to obtain phonons in crystals: namely, we use the Discrete
Fourier Transform from this intermediate space to obtain a block-diagonal
matrix that is readily diagonalizable. We formulate this for general Objective
Structures and then apply it to study carbon nanotubes of various chiralities
that are subjected to axial elongation and torsional deformation. We compare
the phonon spectra computed in the Objective Framework with spectra computed
for armchair and zigzag nanotubes. We also demonstrate the approach by
computing the Density of States. In addition to the computational efficiency
afforded by Objective Structures in providing the transformations to
almost-diagonalize the Hessian, the framework provides an important conceptual
simplification to interpret the phonon curves.Comment: To appear in J. Mech. Phys. Solid
Noise and vibration from building-mounted micro wind turbines Part 2: Results of measurements and analysis
Description
To research the quantification of vibration from a micro turbine, and to develop a method of prediction of vibration and structure borne noise in a wide variety of installations in the UK.
Objective
The objectives of the study are as follows:
1) Develop a methodology to quantify the amount of source vibration from a building mounted micro wind turbine installation, and to predict the level of vibration and structure-borne noise impact within such buildings in the UK.
2) Test and validate the hypothesis on a statically robust sample size
3) Report the developed methodology in a form suitable for widespread adoption by industry and regulators, and report back on the suitability of the method on which to base policy decisions for a future inclusion for building mounted turbines in the GPDO
Chromatographic immunoassays: strategies and recent developments in the analysis of drugs and biological agents
A chromatographic immunoassay is a technique in which an antibody or antibodyrelated agent is used as part of a chromatographic system for the isolation or measurement of a specific target. Various binding agents, detection methods, supports and assay formats have been developed for this group of methods, and applications have been reported that range from drugs, hormones and herbicides to peptides, proteins and bacteria. This review discusses the general principles and applications of chromatographic immunoassays, with an emphasis being given to methods and formats that have been developed for the analysis of drugs and biological agents. The relative advantages or limitations of each format are discussed. Recent developments and research in this field, as well as possible future directions, are also considered
Design and Demonstration of a New Small-Scale Jet Noise Experiment
A facility capable of acoustic and velocity field measurements of high-speed jets has
recently been built and tested. The anechoic chamber that houses the jet has a 2.1 m
Ă— 2.3 m Ă— 2.5 m wedge tip to wedge tip working volume. We aim to demonstrate that
useful experiments can be performed in such a relatively small facility for a substantially
lower cost than in larger facility. Rapid prototyping allows for quick manufacturing of both
simple and complex geometry nozzles. Sideline and 30° downstream acoustic measurements
between 400 Hz and 100 kHz agree well with accepted results. Likewise, nozzle exit-plane
data obtained using particle image velocimetry are in good agreement with other studies
A KIM-compliant potfit for fitting sloppy interatomic potentials : application to the EDIP model for silicon
Fitted interatomic potentials are widely used in atomistic simulations thanks to their ability to compute the energy and forces on atoms quickly. However, the simulation results crucially depend on the quality of the potential being used. Force matching is a method aimed at constructing reliable and transferable interatomic potentials by matching the forces computed by the potential as closely as possible, with those obtained from first principles calculations. The potfit program is an implementation of the force-matching method that optimizes the potential parameters using a global minimization algorithm followed by a local minimization polish. We extended potfit in two ways. First, we adapted the code to be compliant with the KIM Application Programming Interface (API) standard (part of the Knowledgebase of Interatomic Models Project). This makes it possible to use potfit to fit many KIM potential models, not just those prebuilt into the potfit code. Second, we incorporated the geodesic Levenberg–Marquardt (LM) minimization algorithm into potfit as a new local minimization algorithm. The extended potfit was tested by generating a training set using the KIM Environment-Dependent Interatomic Potential (EDIP) model for silicon and using potfit to recover the potential parameters from different initial guesses. The results show that EDIP is a “sloppy model” in the sense that its predictions are insensitive to some of its parameters, which makes fitting more difficult. We find that the geodesic LM algorithm is particularly efficient for this case. The extended potfit code is the first step in developing a KIM-based fitting framework for interatomic potentials for bulk and two-dimensional materials. The code is available for download via https://www.potfit.net
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