Steepest entropy ascent quantum thermodynamic model of electron and phonon transport

2018

Phys. Rev. E

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This paper presents a nonequilibrium, first-principles, thermodynamic-ensemble based model for the relaxation process of interacting non-equilibrium systems. This model is formulated using steepest-entropy-ascent quantum thermodynamics (SEAQT) and its equation of motion for a grand canonical ensemble and is applied to a many particle system of classical or indistinguishable particles. Two kinds of interactions are discussed, including pure heat diffusion and heat and mass diffusion together. Since no local equilibrium assumption is made, the conjugate fluxes and forces are intrinsic to the subspaces of the state space of one system and/or of the state space of two interacting systems. They are derived via the concepts of hypoequilibrium state and nonequilibrium intensive properties, which describe the nonmutual equilibrium status between subspaces of the thermodynamic state space of a single system and/or of the state space of two interacting systems. The Onsager relations are shown to be thermodynamic kinematic features of the system and are found without knowledge of the detailed mechanics of the dynamic process. A fundamental thermodynamic explanation for the measurement of each intensive property of a system in a nonequilibrium state is given. The fundamental thermodynamic definition of reservoir is also discussed. In addition, the equation of motion for a system undergoing multiple interactions is provided, which permits the modeling of a network of local systems in nonequilibrium at any spatial and temporal scale. Finally, the physical features of a nonequilibrium measurement is illustrated via a case study, and the general validity of the equal probability condition is discussed.

Section: Introductionmentioning

confidence: 99%

Steepest-entropy-ascent model of mesoscopic quantum systems far from equilibrium along with generalized thermodynamic definitions of measurement and reservoir

2018

Phys. Rev. E

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“…Relaxation processes in terms of these intensive properties demonstrate the magneto-caloric effect in a straight-forward way. More complex behavior arising from interactions between magnetic spin and a lattice can be incorporated readily into the pseudo-eigenstructure with approaches analogous to SEAQT models of thermal expansion [28] or electron-phonon coupling at an interface [32].…”

Section: Discussionmentioning

confidence: 99%

“…3 and 4 and the remaining figures below is normalized by the relaxation time, τ . This time can be correlated with the real time, t, via comparisons to experimental data [24,25,27] or from ab initio calculations [20,28,32]. Real-time scaling for magnetic relaxation processes has been done in spin The calculated relaxation processes of magnetization from two different initial states prepared using the gamma function, Eq.…”

Section: System Reservoirmentioning

confidence: 99%

“…Within the SEAQT theoretical framework, Li and von Spakovsky have developed the concept of hypoequilibrium states [21,22] (i.e., a non-equilibrium relaxation pattern) and used the concept to define "fundamental", i.e., canonical or grand canonical, non-equilibrium intensive properties such as temperature, chemical potential, and pressure. Using these non-equilibrium intensive properties, Li, von Spakovsky, and Hin have applied the SEAQT framework to the coupled transport of phonons and electrons, clearly distinguishing the nonequilibrium temperatures of phonons and electrons, and showed that the SEAQT equation of motion recovers the two-temperature model of electron-phonon coupling when a constant relaxation time for phonons and electrons is assumed [32]. They also have proven that the SEAQT formulation reduces to the Boltzmann transport equations in the near-equilibrium limit [31,32].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Low-temperature atomistic spin relaxation and non-equilibrium intensive properties using steepest-entropy-ascent quantum-inspired thermodynamics modeling

Yamada

J. Phys.: Condens. Matter

Reynolds

2019

The magnetization of body-centered cubic iron at low temperatures is calculated with the steepestentropy-ascent quantum thermodynamics (SEAQT) framework. This framework assumes that a thermodynamic property in an isolated system traces the path through state space with the greatest entropy production. Magnetization is calculated from the expected value of a thermodynamic ensemble of quantized spin waves based on the Heisenberg spin model applied to an ensemble of coupled harmonic oscillators. A realistic energy landscape is obtained from a magnon dispersion relation calculated using spin-density-functional-theory. The equilibrium magnetization as well as the evolution of magnetization from a non-equilibrium state to equilibrium are calculated from the path of steepest entropy ascent determined from the SEAQT equation of motion in state space. The framework makes it possible to model the temperature-and time-dependence of magnetization without a detailed description of magnetic damping. The approach is also used to define intensive properties (temperature and magnetic field strength) that are fundamentally, i.e., canonically or grand canonically, valid for any non-equilibrium state. Given the assumed magnon dispersion relation, the SEAQT framework is used to calculate the equilibrium magnetization at different temperatures and external magnetic fields and the results are shown to closely agree with experiment for temperatures less than 500 K. The time-dependent evolution of magnetization from different initial states and interactions with a reservoir is also predicted. arXiv:1809.10619v2 [cond-mat.mtrl-sci]

“…With both effects incorporated into the model, the structure of the system's state space as well as the relaxation time 4 of its equation of motion changes throughout the nonequilibrium evolution, accounting intrinsically for the additional polarization. As indicated earlier, the functional form of 4 can be derived ab initio as is done in [40] or from Fermi's golden rule [46] via a classical mechanical scattering process.…”

Section: Parameter Estimationmentioning

confidence: 99%

Multiscale Transient and Steady-State Study of the Influence of Microstructure Degradation and Chromium Oxide Poisoning on Solid Oxide Fuel Cell Cathode Performance

Journal of Non-Equilibrium Thermodynamics

Shen

et al. 2018

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Oxygen reduction in a solid oxide fuel cell cathode involves a nonequilibrium process of coupled mass and heat diffusion and electrochemical and chemical reactions. These phenomena occur at multiple temporal and spatial scales, making the modeling, especially in the transient regime, very difficult. Nonetheless, multiscale models are needed to improve the understanding of oxygen reduction and guide cathode design. Of particular importance for long-term operation are microstructure degradation and chromium oxide poisoning both of which degrade cathode performance. Existing methods are phenomenological or empirical in nature and their application limited to the continuum realm with quantum effects not captured. In contrast, steepest-entropy-ascent quantum thermodynamics can be used to model nonequilibrium processes (even those far-from equilibrium) at all scales. The nonequilibrium relaxation is characterized by entropy generation, which can unify coupled phenomena into one framework to model transient and steady behavior. The results reveal the effects on performance of the different timescales of the varied phenomena involved and their coupling. Results are included here for the effects of chromium oxide concentrations on cathode output as is a parametric study of the effects of interconnect-three-phase-boundary length, oxygen mean free path, and adsorption site effectiveness. A qualitative comparison with experimental results is made.