The Experts below are selected from a list of 33819 Experts worldwide ranked by ideXlab platform
Alan T Dorsey - One of the best experts on this subject based on the ideXlab platform.
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surface tension and Kinetic Coefficient for the normal superconducting interface numerical results versus asymptotic analysis
Physical Review B, 1994Co-Authors: James C Osborn, Alan T DorseyAbstract:The dynamics of the normal/superconducting interface in type-I superconductors has recently been derived from the time-dependent Ginzburg-Landau theory of superconductivity. In a suitable limit these equations are mapped onto a ``free-boundary'' problem, in which the interfacial dynamics are determined by the diffusion of magnetic flux in the normal phase. The magnetic field at the interface satisfies a modified Gibbs-Thomson boundary condition which involves both the surface tension of the interface and a Kinetic Coefficient for motion of the interface. In this paper we calculate the surface tension and Kinetic Coefficient numerically by solving the one dimensional equilibrium Ginzburg-Landau equations for a wide range of $\kappa$ values. We compare our numerical results to asymptotic expansions valid for $\kappa\ll 1$, $\kappa\approx 1/\sqrt{2}$, and $\kappa\gg 1$, in order to determine the accuracy of these expansions.
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Surface tension and Kinetic Coefficient for the normal/superconducting interface: Numerical results versus asymptotic analysis.
Physical review. B Condensed matter, 1994Co-Authors: James C Osborn, Alan T DorseyAbstract:The dynamics of the normal/superconducting interface in type-I superconductors has recently been derived from the time-dependent Ginzburg-Landau theory of superconductivity. In a suitable limit these equations are mapped onto a ``free-boundary'' problem, in which the interfacial dynamics are determined by the diffusion of magnetic flux in the normal phase. The magnetic field at the interface satisfies a modified Gibbs-Thomson boundary condition which involves both the surface tension of the interface and a Kinetic Coefficient for motion of the interface. In this paper we calculate the surface tension and Kinetic Coefficient numerically by solving the one dimensional equilibrium Ginzburg-Landau equations for a wide range of $\kappa$ values. We compare our numerical results to asymptotic expansions valid for $\kappa\ll 1$, $\kappa\approx 1/\sqrt{2}$, and $\kappa\gg 1$, in order to determine the accuracy of these expansions.
J J Hoyt - One of the best experts on this subject based on the ideXlab platform.
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Kinetic Coefficient of steps at the si 111 crystal melt interface from molecular dynamics simulations
Journal of Chemical Physics, 2007Co-Authors: Dorel Buta, Mark Asta, J J HoytAbstract:In the growth of crystals from the melt or solution the properties of solid-liquid interfaces often play a critical role controlling morphology and defect densities. In the case of inorganic materials grown from their melt phase, quantitative modeling of solidification is often hindered by a lack of detailed experimental data concerning the intrinsic properties of crystal-melt interfaces. Specifically, modeling of nucleation and solidification growth morphologies requires knowledge of the magnitudes and associated crystalline anisotropies of the crystal-melt interfacial free energies and mobilities. Due to the inherent difficulty associated with direct experimental studies of solid-liquid interfaces at high temperatures, measured data for the properties of crystalmelt interfaces are presently available for very few systems. Since the pioneering work of Broughton et al. 1 much of the most detailed information concerning the intrinsic properties of crystal-melt interfaces has been derived from atomic-scale molecular dynamics MD and Monte Carlo simulations. Such simulations have determined the magnitudes and
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crystal melt interfacial free energies and mobilities in fcc and bcc fe
Physical Review B, 2004Co-Authors: Mark Asta, J J HoytAbstract:Molecular-dynamics simulations have been used to compute thermodynamic and Kinetic properties of the solid-liquid interface for both the fcc and bcc phases of Fe. Pure Fe was modeled using two different interatomic potentials of the embedded atom type as well as an effective pair potential. Free solidification simulations were used to determine the Kinetic Coefficient $\ensuremath{\mu}$ for the different models of pure Fe. The anisotropy of $\ensuremath{\mu}$ with respect to growth direction in the bcc phase is similar to that observed in fcc systems, namely ${\ensuremath{\mu}}_{100}g{\ensuremath{\mu}}_{110}\ensuremath{\sim}{\ensuremath{\mu}}_{111},$ and the Kinetic Coefficient of bcc is larger than $\ensuremath{\mu}$ for the fcc phase. The Kinetic Coefficient results are discussed in terms of a Kinetic density-functional-theory-based model of crystal growth. In addition, results for solid-liquid interfacial free energies $\ensuremath{\gamma}$ computed via the capillary fluctuation method, are summarized.
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atomistic computation of liquid diffusivity solid liquid interfacial free energy and Kinetic Coefficient in au and ag
Physical Review B, 2002Co-Authors: J J Hoyt, Mark AstaAbstract:Molecular-dynamics simulations using interatomic potentials of the embedded atom method have been performed on pure Ag and Au to compute materials parameters which are necessary for continuum modeling of dendritic solidification. The liquid state diffusion Coefficient has been determined for temperatures in the vicinity of the melting points and good agreement with experimental data available for Ag is found. The Kinetic Coefficients for Au and Ag have been determined by monitoring the velocity of the solid-liquid interface as a function of undercooling. Rates of crystallization for the 100 and 110 directions agree well with a model proposed by Broughton, Gilmer and Jackson [Phys. Rev. Lett. 49, 1496 (1982)] whereas the 111 direction exhibits a slower growth rate consistent with the presence of stacking fault clusters on the solid-liquid boundary, which anneal out during solidification. The solid-liquid interfacial free energy and its anisotropy have been obtained for Ag and Au by monitoring equilibrium fluctuations in the interface position. The fluctuation spectrum technique allows for an accurate determination of very small anisotropies in the interfacial energy and we find an anisotropy factor $1.0\ifmmode\pm\else\textpm\fi{}0.3%$ for Ag and $1.6\ifmmode\pm\else\textpm\fi{}0.3%$ for Au.
Mark Asta - One of the best experts on this subject based on the ideXlab platform.
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Determination of the crystal-melt interface Kinetic Coefficient from molecular dynamics simulations
Modelling and Simulation in Materials Science and Engineering, 2009Co-Authors: Joshua Monk, Yang Yang, Mikhail I. Mendelev, Mark Asta, Jeffrey J. Hoyt, Deyan SunAbstract:The generation and dissipation of latent heat at the moving solid–liquid boundary during non-equilibrium molecular dynamics (MD) simulations of crystallization can lead to significant underestimations of the interface mobility. In this work we examine the heat flow problem in detail for an embedded atom description of pure Ni and offer strategies to obtain an accurate value of the Kinetic Coefficient, μ. For free-solidification simulations in which the entire system is thermostated using a Nose–Hoover or velocity rescaling algorithm a non-uniform temperature profile is observed and a peak in the temperature is found at the interface position. It is shown that if the actual interface temperature, rather than the thermostat set point temperature, is used to compute the Kinetic Coefficient then μ is approximately a factor of 2 larger than previous estimates. In addition, we introduce a layered thermostat method in which several sub-regions, aligned normal to the crystallization direction, are indepently thermostated to a desired undercooling. We show that as the number of thermostats increases (i.e., as the width of each independently thermostated layer decreases) the Kinetic Coefficient converges to a value consistent with that obtained using a single thermostat and the calculated interface temperature. Also, the Kinetic Coefficient was determined from an analysis of the equilibrium fluctuations of the solid–liquid interface position. We demonstrate that the Kinetic Coefficient obtained from the relaxation times of the fluctuation spectrum is equivalent to the two values obtained from free-solidification simulations provided a simple correction is made for the contribution of heat flow controlled interface motion. Finally, a one-dimensional phase field model that captures the effect of thermostats has been developed. The mesoscale model reproduces qualitatively the results from MD simulations and thus allows for an a priori estimate of the accuracy of a Kinetic Coefficient determination for any given classical MD system. The model also elucidates that the magnitude of the temperature gradients obtained in simulations with a single thermostat depends on the length of the simulation system normal to the interface; the need for the corrections discussed in this paper can thus be gauged from a study of the dependence of the calculated Kinetic Coefficient on system size.
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Kinetic Coefficient of steps at the si 111 crystal melt interface from molecular dynamics simulations
Journal of Chemical Physics, 2007Co-Authors: Dorel Buta, Mark Asta, J J HoytAbstract:In the growth of crystals from the melt or solution the properties of solid-liquid interfaces often play a critical role controlling morphology and defect densities. In the case of inorganic materials grown from their melt phase, quantitative modeling of solidification is often hindered by a lack of detailed experimental data concerning the intrinsic properties of crystal-melt interfaces. Specifically, modeling of nucleation and solidification growth morphologies requires knowledge of the magnitudes and associated crystalline anisotropies of the crystal-melt interfacial free energies and mobilities. Due to the inherent difficulty associated with direct experimental studies of solid-liquid interfaces at high temperatures, measured data for the properties of crystalmelt interfaces are presently available for very few systems. Since the pioneering work of Broughton et al. 1 much of the most detailed information concerning the intrinsic properties of crystal-melt interfaces has been derived from atomic-scale molecular dynamics MD and Monte Carlo simulations. Such simulations have determined the magnitudes and
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crystal melt interfacial free energies and mobilities in fcc and bcc fe
Physical Review B, 2004Co-Authors: Mark Asta, J J HoytAbstract:Molecular-dynamics simulations have been used to compute thermodynamic and Kinetic properties of the solid-liquid interface for both the fcc and bcc phases of Fe. Pure Fe was modeled using two different interatomic potentials of the embedded atom type as well as an effective pair potential. Free solidification simulations were used to determine the Kinetic Coefficient $\ensuremath{\mu}$ for the different models of pure Fe. The anisotropy of $\ensuremath{\mu}$ with respect to growth direction in the bcc phase is similar to that observed in fcc systems, namely ${\ensuremath{\mu}}_{100}g{\ensuremath{\mu}}_{110}\ensuremath{\sim}{\ensuremath{\mu}}_{111},$ and the Kinetic Coefficient of bcc is larger than $\ensuremath{\mu}$ for the fcc phase. The Kinetic Coefficient results are discussed in terms of a Kinetic density-functional-theory-based model of crystal growth. In addition, results for solid-liquid interfacial free energies $\ensuremath{\gamma}$ computed via the capillary fluctuation method, are summarized.
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Kinetic Coefficient of Ni solid-liquid interfaces from molecular-dynamics simulations
Physical Review B, 2004Co-Authors: Deyan Sun, Mark Asta, Jeffrey J. HoytAbstract:The Kinetics of isothermal crystallization and melting are studied for elemental Ni employing non-equilibrium molecular-dynamics simulations based on interatomic potentials of the embedded-atom-method form. These simulations form the basis for calculations of the magnitude and crystalline anisotropy of the Kinetic Coefficient $\ensuremath{\mu},$ defined as the constant of proportionality between interface velocity and undercooling. We obtain highly symmetric rates for crystallization and melting, from which we extract the following values of $\ensuremath{\mu}$ for low index ${100},$ ${110},$ and ${111}$ interfaces: ${\ensuremath{\mu}}_{100}=35.8\ifmmode\pm\else\textpm\fi{}22,$ ${\ensuremath{\mu}}_{110}=25.5\ifmmode\pm\else\textpm\fi{}1.6,$ and ${\ensuremath{\mu}}_{111}=24.1\ifmmode\pm\else\textpm\fi{}4.0$ in units of cm/s K. The results of the present study are discussed in the context of previous molecular-dynamics simulations for related systems, and Kinetic models based upon transition-state and density-functional theories.
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Atomistic Simulation Methods for Computing the Kinetic Coefficient in Solid-Liquid Systems
Interface Science, 2002Co-Authors: Jeffrey J. Hoyt, Mark Asta, Alain KarmaAbstract:The Kinetic Coefficient, μ, is the constant of proportionality between the velocity of a solid-liquid interface and the interface undercooling. The value of μ and its anisotropy are critical parameters in phase field modeling of dendritic solidification. In this paper we review several different molecular dynamics simulation methods which have been proposed to compute the Kinetic Coefficient. Techniques based on forced velocity simulations, free solidification simulations and fluctuation analyses are discussed and compared. In addition, a model of crystalline growth Kinetics due to Broughton, Gilmer and Jackson will be compared with available atomistic simulation data.
James C Osborn - One of the best experts on this subject based on the ideXlab platform.
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surface tension and Kinetic Coefficient for the normal superconducting interface numerical results versus asymptotic analysis
Physical Review B, 1994Co-Authors: James C Osborn, Alan T DorseyAbstract:The dynamics of the normal/superconducting interface in type-I superconductors has recently been derived from the time-dependent Ginzburg-Landau theory of superconductivity. In a suitable limit these equations are mapped onto a ``free-boundary'' problem, in which the interfacial dynamics are determined by the diffusion of magnetic flux in the normal phase. The magnetic field at the interface satisfies a modified Gibbs-Thomson boundary condition which involves both the surface tension of the interface and a Kinetic Coefficient for motion of the interface. In this paper we calculate the surface tension and Kinetic Coefficient numerically by solving the one dimensional equilibrium Ginzburg-Landau equations for a wide range of $\kappa$ values. We compare our numerical results to asymptotic expansions valid for $\kappa\ll 1$, $\kappa\approx 1/\sqrt{2}$, and $\kappa\gg 1$, in order to determine the accuracy of these expansions.
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Surface tension and Kinetic Coefficient for the normal/superconducting interface: Numerical results versus asymptotic analysis.
Physical review. B Condensed matter, 1994Co-Authors: James C Osborn, Alan T DorseyAbstract:The dynamics of the normal/superconducting interface in type-I superconductors has recently been derived from the time-dependent Ginzburg-Landau theory of superconductivity. In a suitable limit these equations are mapped onto a ``free-boundary'' problem, in which the interfacial dynamics are determined by the diffusion of magnetic flux in the normal phase. The magnetic field at the interface satisfies a modified Gibbs-Thomson boundary condition which involves both the surface tension of the interface and a Kinetic Coefficient for motion of the interface. In this paper we calculate the surface tension and Kinetic Coefficient numerically by solving the one dimensional equilibrium Ginzburg-Landau equations for a wide range of $\kappa$ values. We compare our numerical results to asymptotic expansions valid for $\kappa\ll 1$, $\kappa\approx 1/\sqrt{2}$, and $\kappa\gg 1$, in order to determine the accuracy of these expansions.
Jeffrey J. Hoyt - One of the best experts on this subject based on the ideXlab platform.
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Ginzburg-Landau theory of the bcc-liquid interface Kinetic Coefficient
Physical Review B, 2015Co-Authors: Ching-hao Wang, Jeffrey J. Hoyt, Alain KarmaAbstract:We extend the Ginzburg-Landau (GL) theory of atomically rough bcc-liquid interfaces [Wu et al., Phys. Rev. B 73, 094101 (2006)] outside of equilibrium. We use this extension to derive an analytical expression for the Kinetic Coefficient, which is the proportionality constant $\ensuremath{\mu}(\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{n})$ between the interface velocity along a direction $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{n}$ normal to the interface and the interface undercooling. The Kinetic Coefficient is expressed as a spatial integral along the normal direction of a sum of gradient square terms corresponding to different nonlinear density wave profiles. Anisotropy arises naturally from the dependence of those profiles on the angles between the principal reciprocal lattice vectors ${\stackrel{P\vec}{K}}_{i}$ and $\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{n}$. Values of the Kinetic Coefficient for the $(100),\phantom{\rule{0.16em}{0ex}}(110)$, and $(111)$ interfaces are compared quantitatively to the prediction of linear Mikheev-Chernov (MC) theory [J. Cryst. Growth 112, 591 (1991)] and previous molecular dynamics (MD) simulation studies of crystallization Kinetics for a classical model of Fe. Additional MD simulations are carried out here to compute the relaxation time of density waves in the liquid in order to make this comparison free of fit parameters. The GL theory predicts an expression for $\ensuremath{\mu}$ similar to the MC theory but yields a better agreement with MD simulations for both its magnitude and anisotropy due to a fully nonlinear description of density wave profiles across the solid-liquid interface. In particular, the overall magnitude of $\ensuremath{\mu}$ predicted by GL theory is an order of magnitude larger than predicted by the MC theory. GL theory is also used to derive an inverse relation between $\ensuremath{\mu}$ and the solid-liquid interfacial free energy. The general methodology used here to derive an expression for $\ensuremath{\mu}(\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{n})$ also applies to amplitude equations derived from the phase-field-crystal model, which only differ from GL theory by the choice of cubic and higher order nonlinearities in the free-energy density.
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Determination of the crystal-melt interface Kinetic Coefficient from molecular dynamics simulations
Modelling and Simulation in Materials Science and Engineering, 2009Co-Authors: Joshua Monk, Yang Yang, Mikhail I. Mendelev, Mark Asta, Jeffrey J. Hoyt, Deyan SunAbstract:The generation and dissipation of latent heat at the moving solid–liquid boundary during non-equilibrium molecular dynamics (MD) simulations of crystallization can lead to significant underestimations of the interface mobility. In this work we examine the heat flow problem in detail for an embedded atom description of pure Ni and offer strategies to obtain an accurate value of the Kinetic Coefficient, μ. For free-solidification simulations in which the entire system is thermostated using a Nose–Hoover or velocity rescaling algorithm a non-uniform temperature profile is observed and a peak in the temperature is found at the interface position. It is shown that if the actual interface temperature, rather than the thermostat set point temperature, is used to compute the Kinetic Coefficient then μ is approximately a factor of 2 larger than previous estimates. In addition, we introduce a layered thermostat method in which several sub-regions, aligned normal to the crystallization direction, are indepently thermostated to a desired undercooling. We show that as the number of thermostats increases (i.e., as the width of each independently thermostated layer decreases) the Kinetic Coefficient converges to a value consistent with that obtained using a single thermostat and the calculated interface temperature. Also, the Kinetic Coefficient was determined from an analysis of the equilibrium fluctuations of the solid–liquid interface position. We demonstrate that the Kinetic Coefficient obtained from the relaxation times of the fluctuation spectrum is equivalent to the two values obtained from free-solidification simulations provided a simple correction is made for the contribution of heat flow controlled interface motion. Finally, a one-dimensional phase field model that captures the effect of thermostats has been developed. The mesoscale model reproduces qualitatively the results from MD simulations and thus allows for an a priori estimate of the accuracy of a Kinetic Coefficient determination for any given classical MD system. The model also elucidates that the magnitude of the temperature gradients obtained in simulations with a single thermostat depends on the length of the simulation system normal to the interface; the need for the corrections discussed in this paper can thus be gauged from a study of the dependence of the calculated Kinetic Coefficient on system size.
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Kinetic Coefficient of Ni solid-liquid interfaces from molecular-dynamics simulations
Physical Review B, 2004Co-Authors: Deyan Sun, Mark Asta, Jeffrey J. HoytAbstract:The Kinetics of isothermal crystallization and melting are studied for elemental Ni employing non-equilibrium molecular-dynamics simulations based on interatomic potentials of the embedded-atom-method form. These simulations form the basis for calculations of the magnitude and crystalline anisotropy of the Kinetic Coefficient $\ensuremath{\mu},$ defined as the constant of proportionality between interface velocity and undercooling. We obtain highly symmetric rates for crystallization and melting, from which we extract the following values of $\ensuremath{\mu}$ for low index ${100},$ ${110},$ and ${111}$ interfaces: ${\ensuremath{\mu}}_{100}=35.8\ifmmode\pm\else\textpm\fi{}22,$ ${\ensuremath{\mu}}_{110}=25.5\ifmmode\pm\else\textpm\fi{}1.6,$ and ${\ensuremath{\mu}}_{111}=24.1\ifmmode\pm\else\textpm\fi{}4.0$ in units of cm/s K. The results of the present study are discussed in the context of previous molecular-dynamics simulations for related systems, and Kinetic models based upon transition-state and density-functional theories.
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Atomistic Simulation Methods for Computing the Kinetic Coefficient in Solid-Liquid Systems
Interface Science, 2002Co-Authors: Jeffrey J. Hoyt, Mark Asta, Alain KarmaAbstract:The Kinetic Coefficient, μ, is the constant of proportionality between the velocity of a solid-liquid interface and the interface undercooling. The value of μ and its anisotropy are critical parameters in phase field modeling of dendritic solidification. In this paper we review several different molecular dynamics simulation methods which have been proposed to compute the Kinetic Coefficient. Techniques based on forced velocity simulations, free solidification simulations and fluctuation analyses are discussed and compared. In addition, a model of crystalline growth Kinetics due to Broughton, Gilmer and Jackson will be compared with available atomistic simulation data.
