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ICS-2 Seminar: Maintaining the equipartition theorem in small heterogeneous molecular dynamics ensembles


Nima H. Siboni

Max-Planck-Institut für Eisenforschung GmbH, Düsseldorf

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26.Sep.2013 11:00
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Seminarraum 2001, Geb. 04.16

Theorie-Seminar

The equipartition theorem, as one of the fundamental theorems of the equilibrium statistical physics, served as a tool to measure and control the temperature in computer simulations. Its application has been extended even to non-equilibrium cases, where the temperature is not a well-defined quantity [1,2]. But it has been reported recently that the equipartition theorem is violated in molecular dynamics simulations with periodic boundary condition [3]. This effect is associated with the conservation of the total momentum. I will talk about our fluctuating center of mass molecular dynamics approach to solve this problem [4]. Using the analogy to a system exchanging momentum with its surroundings, we work out—and validate via simulations—an expression for the rate at which fluctuations shall be added to the system. It is shown that the proposed method maintains equipartition both at equilibrium and beyond equilibrium in the linear response regime.

[1] L. Berthier and J.-L. Barrat. Nonequilibrium dynamics and fluctuation-dissipation relation in a sheared fluid, J. Chem. Phys., 116(14):6228–62[42, 2002.

[2] D. Loi, S. Mossa, and L. F. Cugliandolo. Effective temperature of active matter. Phys. Rev. E, 77:051111, May 2008.

[3] R. B. Shirts, S. R. Burt, A. M. Johnson, Periodic boundary condition induced breakdown of the equipartition principle and other kinetic effects of finite sample size in classical hard-sphere molecular dynamics simulation, J. Chem. Phys., 125 164102 (2006)

[4] N. H. Siboni, D. Raabe, and F. Varnik, Maintaining the equipartition theorem in small heterogeneous molecular dynamics ensembles, Phys. Rev. E 87, 030101(R) (2013).

Contact

Prof. Dr. Gerhard Gompper
Phone: +49 2461 61-4012
Fax: +49 2461 61-3180
email: g.gompper@fz-juelich.de

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