The Experts below are selected from a list of 24458091 Experts worldwide ranked by ideXlab platform
Longqing Chen - One of the best experts on this subject based on the ideXlab platform.
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first principles thermodynamic theory of seebeck coefficients
Physical Review B, 2018Co-Authors: Yi Wang, Bicheng Zhou, Brandon Bocklund, Shunli Shang, Yongjie Hu, Longqing ChenAbstract:Thermoelectric effects, measured by the Seebeck coefficients, refer to the phenomena in which a temperature difference or gradient imposed across a thermoelectric material induces an electrical potential difference or gradient, and vice versa, enabling the direct conversion of thermal and electric energies. All existing understanding and First-Principles calculations of Seebeck coefficients have been based on the Boltzmann kinetic transport theory. Here we demonstrate that the Seebeck coefficient is a well-defined thermodynamic quantity that can be determined from the change in the chemical potential of electrons induced by the temperature change and thus can be efficiently computed solely based on the electronic density of states through First-Principles calculations at different temperatures. The proposed approach is demonstrated using the prototype PbTe and SnSe thermoelectric materials. The proposed thermodynamic approach dramatically simplifies the calculations of Seebeck coefficients, making it possible to search for high performance thermoelectric materials using high-throughput First-Principles calculations.
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first principles impurity diffusion coefficients
Acta Materialia, 2009Co-Authors: M Mantina, Longqing Chen, Yi Wang, Zi Kui Liu, Chris WolvertonAbstract:Abstract We report the prediction of impurity diffusion coefficients entirely from first principles, using density-functional theory (DFT) calculations. From DFT we obtain all microscopic parameters in the pre-factor and activation energy of impurity diffusion coefficients: (i) the correlation factor through a five frequency model, (ii) the impurity jump frequency within the framework of transition state theory and (iii) the free energies of vacancy formation and vacancy–solute binding. Specifically, we calculate the impurity diffusion coefficients of Mg, Si and Cu in dilute face-centered cubic Al alloys. The results show excellent agreement with experimental data. We discuss the factors contributing to the trends in diffusivities of these impurities.
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first principles calculation of self diffusion coefficients
Physical Review Letters, 2008Co-Authors: M Mantina, Longqing Chen, Yi Wang, Zi Kui Liu, Raymundo Arroyave, Chris WolvertonAbstract:We demonstrate a First-Principles method to compute all factors entering the vacancy-mediated self-diffusion coefficient. Using density functional theory calculations of fcc Al as an illustrative case, we determine the energetic and entropic contributions to vacancy formation and atomic migration. These results yield a quantitative description of the migration energy and vibrational prefactor via transition state theory. The calculated diffusion parameters and coefficients show remarkably good agreement with experiments. We provide a simple physical picture for the positive entropic contributions.
Chris Wolverton - One of the best experts on this subject based on the ideXlab platform.
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first principles impurity diffusion coefficients
Acta Materialia, 2009Co-Authors: M Mantina, Longqing Chen, Yi Wang, Zi Kui Liu, Chris WolvertonAbstract:Abstract We report the prediction of impurity diffusion coefficients entirely from first principles, using density-functional theory (DFT) calculations. From DFT we obtain all microscopic parameters in the pre-factor and activation energy of impurity diffusion coefficients: (i) the correlation factor through a five frequency model, (ii) the impurity jump frequency within the framework of transition state theory and (iii) the free energies of vacancy formation and vacancy–solute binding. Specifically, we calculate the impurity diffusion coefficients of Mg, Si and Cu in dilute face-centered cubic Al alloys. The results show excellent agreement with experimental data. We discuss the factors contributing to the trends in diffusivities of these impurities.
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first principles calculation of self diffusion coefficients
Physical Review Letters, 2008Co-Authors: M Mantina, Longqing Chen, Yi Wang, Zi Kui Liu, Raymundo Arroyave, Chris WolvertonAbstract:We demonstrate a First-Principles method to compute all factors entering the vacancy-mediated self-diffusion coefficient. Using density functional theory calculations of fcc Al as an illustrative case, we determine the energetic and entropic contributions to vacancy formation and atomic migration. These results yield a quantitative description of the migration energy and vibrational prefactor via transition state theory. The calculated diffusion parameters and coefficients show remarkably good agreement with experiments. We provide a simple physical picture for the positive entropic contributions.
Matthias Fuchs - One of the best experts on this subject based on the ideXlab platform.
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first principles constitutive equation for suspension rheology
Physical Review E, 2012Co-Authors: Joseph M Brader, Michael E. Cates, Matthias FuchsAbstract:The imposition of flow can drive a fluid far from equilibrium. Because of the occurrence of long relaxation times, this effect is ubiquitous in complex fluids (colloids, polymers, etc.) whose rheology is of significant technological interest, and also represents an important challenge in nonequilibrium statistical physics. Continuum approaches have provided important insights, using symmetry and other principles to construct or constrain phenomenological constitutive relations. While the constitutive equations of Newtonian fluids and Hookian solids are derivable from fundamental starting points (the theory of linear response based on Onsager’s regression hypothesis), there has been less progress with their nonlinear generalizations for viscoelastic fluids, plastic solids and other strongly deforming soft materials. A central aim of theoretical rheology is thus to derive from the underlying microscopic interactions the constitutive equations that relate the stress tensor to the macroscopic deformation history of a material. For entangled polymer melts, the constitutive equation of Doi and Edwards [1] has enjoyed considerable success. An analogously general microscopic constitutive equation for colloidal dispersions remains conspicuously lacking [2]. Even the simplest hard-sphere colloids in concentrated suspension exhibit a broad range of viscoelastic behavior; alongside to flow-thinning [3] and thickening [4], slow structural relaxation leads to glasses showing a solidlike response, strain hardening or softening, and plastic flow [5]. But, while the linear viscoelastic spectra of colloidal suspensions are fairly well understood [6], only recently has progress been made in nonlinear flow predictions for simple shear [7,8]. Shear represents a relatively weak flow in which material lines grow linearly with time, while in elongational flows such growth is exponential, creating much more severe deformations of material elements. Thus, a description capable of handling arbitrary deformation histories is highly desirable. In the continuum approaches, invariance arguments strongly restrict the
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first principles constitutive equation for suspension rheology
Physical Review Letters, 2008Co-Authors: Joseph M Brader, Michael E. Cates, Matthias FuchsAbstract:Using mode-coupling theory, we derive a constitutive equation for the nonlinear rheology of dense colloidal suspensions under arbitrary time-dependent homogeneous flow. Generalizing previous results for simple shear, this allows the full tensorial structure of the theory to be identified. Macroscopic deformation measures, such as the Cauchy-Green tensors, thereby emerge. So does a direct relation between the stress and the distorted microstructure, illuminating the interplay of slow structural relaxation and arbitrary imposed flow. We present flow curves for steady planar and uniaxial elongation and compare these to simple shear. The resulting nonlinear Trouton ratios point to a tensorially nontrivial dynamic yield condition for colloidal glasses.
Yi Wang - One of the best experts on this subject based on the ideXlab platform.
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first principles thermodynamic theory of seebeck coefficients
Physical Review B, 2018Co-Authors: Yi Wang, Bicheng Zhou, Brandon Bocklund, Shunli Shang, Yongjie Hu, Longqing ChenAbstract:Thermoelectric effects, measured by the Seebeck coefficients, refer to the phenomena in which a temperature difference or gradient imposed across a thermoelectric material induces an electrical potential difference or gradient, and vice versa, enabling the direct conversion of thermal and electric energies. All existing understanding and First-Principles calculations of Seebeck coefficients have been based on the Boltzmann kinetic transport theory. Here we demonstrate that the Seebeck coefficient is a well-defined thermodynamic quantity that can be determined from the change in the chemical potential of electrons induced by the temperature change and thus can be efficiently computed solely based on the electronic density of states through First-Principles calculations at different temperatures. The proposed approach is demonstrated using the prototype PbTe and SnSe thermoelectric materials. The proposed thermodynamic approach dramatically simplifies the calculations of Seebeck coefficients, making it possible to search for high performance thermoelectric materials using high-throughput First-Principles calculations.
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first principles impurity diffusion coefficients
Acta Materialia, 2009Co-Authors: M Mantina, Longqing Chen, Yi Wang, Zi Kui Liu, Chris WolvertonAbstract:Abstract We report the prediction of impurity diffusion coefficients entirely from first principles, using density-functional theory (DFT) calculations. From DFT we obtain all microscopic parameters in the pre-factor and activation energy of impurity diffusion coefficients: (i) the correlation factor through a five frequency model, (ii) the impurity jump frequency within the framework of transition state theory and (iii) the free energies of vacancy formation and vacancy–solute binding. Specifically, we calculate the impurity diffusion coefficients of Mg, Si and Cu in dilute face-centered cubic Al alloys. The results show excellent agreement with experimental data. We discuss the factors contributing to the trends in diffusivities of these impurities.
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first principles calculation of self diffusion coefficients
Physical Review Letters, 2008Co-Authors: M Mantina, Longqing Chen, Yi Wang, Zi Kui Liu, Raymundo Arroyave, Chris WolvertonAbstract:We demonstrate a First-Principles method to compute all factors entering the vacancy-mediated self-diffusion coefficient. Using density functional theory calculations of fcc Al as an illustrative case, we determine the energetic and entropic contributions to vacancy formation and atomic migration. These results yield a quantitative description of the migration energy and vibrational prefactor via transition state theory. The calculated diffusion parameters and coefficients show remarkably good agreement with experiments. We provide a simple physical picture for the positive entropic contributions.
M Mantina - One of the best experts on this subject based on the ideXlab platform.
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first principles impurity diffusion coefficients
Acta Materialia, 2009Co-Authors: M Mantina, Longqing Chen, Yi Wang, Zi Kui Liu, Chris WolvertonAbstract:Abstract We report the prediction of impurity diffusion coefficients entirely from first principles, using density-functional theory (DFT) calculations. From DFT we obtain all microscopic parameters in the pre-factor and activation energy of impurity diffusion coefficients: (i) the correlation factor through a five frequency model, (ii) the impurity jump frequency within the framework of transition state theory and (iii) the free energies of vacancy formation and vacancy–solute binding. Specifically, we calculate the impurity diffusion coefficients of Mg, Si and Cu in dilute face-centered cubic Al alloys. The results show excellent agreement with experimental data. We discuss the factors contributing to the trends in diffusivities of these impurities.
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first principles calculation of self diffusion coefficients
Physical Review Letters, 2008Co-Authors: M Mantina, Longqing Chen, Yi Wang, Zi Kui Liu, Raymundo Arroyave, Chris WolvertonAbstract:We demonstrate a First-Principles method to compute all factors entering the vacancy-mediated self-diffusion coefficient. Using density functional theory calculations of fcc Al as an illustrative case, we determine the energetic and entropic contributions to vacancy formation and atomic migration. These results yield a quantitative description of the migration energy and vibrational prefactor via transition state theory. The calculated diffusion parameters and coefficients show remarkably good agreement with experiments. We provide a simple physical picture for the positive entropic contributions.
