Temperature of nonequilibrium steady-state systems

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Abstract

We determined the operational temperatures of nonequilibrium-molecular-dynamics (NEMD) systems by the recently developed thermometer [A. Baranyai, Phys. Rev. E 61, R3306 (2000)] and compared these values to the dynamic temperatures [H. H. Rough, Phys. Rev. Lett. 78, 772 (1997)] of the same systems. NEMD models use a synthetic thermostat, a numerical feedback procedure to remove the dissipative heat instantaneously. A consequence of this feedback is a splitting of the dynamic temperature. The kinetic part is different from the configurational part because the energy is removed through the momentum subspace of the system. In addition to this, these temperature values also vary with respect to the direction of the external perturbation. In the case of planar Couette flow and color flow, the isotropic operational temperatures of dense liquids are always closer to the configurational than to the kinetic temperatures. We show that the observed split and the pronounced directional dependence of the dynamic temperature is an artifact caused by the instantaneous feedback of NEMD models. Since relaxation of a preset difference between the kinetic and the configurational temperature is an order of magnitude faster than the relaxation of the heat flux vector, for models with realistic thermostas such a split must be very small. We argue that in real systems, even far from equilibrium, the operational temperature and both terms of the dynamic temperature must be practically identical and isotropic.

Original languageEnglish
Pages (from-to)5989-5997
Number of pages9
JournalPhysical Review E - Statistical Physics, Plasmas, Fluids, and Related Interdisciplinary Topics
Volume62
Issue number5 B
Publication statusPublished - Nov 2000

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Nonequilibrium Steady State
Non-equilibrium Molecular Dynamics
temperature
Kinetics
molecular dynamics
dynamic models
Dynamic Model
kinetics
Thermometer
Thermostat
thermostats
Couette Flow
Couette flow
thermometers
Heat Flux
Dynamic Systems
Rough
Instantaneous
artifacts
heat flux

ASJC Scopus subject areas

  • Mathematical Physics
  • Physics and Astronomy(all)
  • Condensed Matter Physics
  • Statistical and Nonlinear Physics

Cite this

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title = "Temperature of nonequilibrium steady-state systems",
abstract = "We determined the operational temperatures of nonequilibrium-molecular-dynamics (NEMD) systems by the recently developed thermometer [A. Baranyai, Phys. Rev. E 61, R3306 (2000)] and compared these values to the dynamic temperatures [H. H. Rough, Phys. Rev. Lett. 78, 772 (1997)] of the same systems. NEMD models use a synthetic thermostat, a numerical feedback procedure to remove the dissipative heat instantaneously. A consequence of this feedback is a splitting of the dynamic temperature. The kinetic part is different from the configurational part because the energy is removed through the momentum subspace of the system. In addition to this, these temperature values also vary with respect to the direction of the external perturbation. In the case of planar Couette flow and color flow, the isotropic operational temperatures of dense liquids are always closer to the configurational than to the kinetic temperatures. We show that the observed split and the pronounced directional dependence of the dynamic temperature is an artifact caused by the instantaneous feedback of NEMD models. Since relaxation of a preset difference between the kinetic and the configurational temperature is an order of magnitude faster than the relaxation of the heat flux vector, for models with realistic thermostas such a split must be very small. We argue that in real systems, even far from equilibrium, the operational temperature and both terms of the dynamic temperature must be practically identical and isotropic.",
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AB - We determined the operational temperatures of nonequilibrium-molecular-dynamics (NEMD) systems by the recently developed thermometer [A. Baranyai, Phys. Rev. E 61, R3306 (2000)] and compared these values to the dynamic temperatures [H. H. Rough, Phys. Rev. Lett. 78, 772 (1997)] of the same systems. NEMD models use a synthetic thermostat, a numerical feedback procedure to remove the dissipative heat instantaneously. A consequence of this feedback is a splitting of the dynamic temperature. The kinetic part is different from the configurational part because the energy is removed through the momentum subspace of the system. In addition to this, these temperature values also vary with respect to the direction of the external perturbation. In the case of planar Couette flow and color flow, the isotropic operational temperatures of dense liquids are always closer to the configurational than to the kinetic temperatures. We show that the observed split and the pronounced directional dependence of the dynamic temperature is an artifact caused by the instantaneous feedback of NEMD models. Since relaxation of a preset difference between the kinetic and the configurational temperature is an order of magnitude faster than the relaxation of the heat flux vector, for models with realistic thermostas such a split must be very small. We argue that in real systems, even far from equilibrium, the operational temperature and both terms of the dynamic temperature must be practically identical and isotropic.

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