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Dresden 2003 – scientific programme

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DY: Dynamik und Statistische Physik

DY 20: Soft matter I

DY 20.2: Talk

Tuesday, March 25, 2003, 10:00–10:15, G\"OR/226

Construction and test of thermostats and twirlers for molecular rotations — •Siegfried Hess — Inst. f. Theoret. Physik, Techn. Univ. Berlin, 10623 Berlin

Time reversible thermostats (Gaussian isokinetic, Nosé-Hoover and generalisations) have found widespread applications in molecular dynamics computer simulations for many particles. When applied to systems of few particles in two or three dimensions it is desireable to have an additional ‘stirring’ or ‘twirling’ mechanism which affects the directions of the velocities and not just their magnitudes as all standard thermostats do. In particular, a randomization of the angular momentum is wanted. This point is evident for the extendable dumbbell model studied recently1,2. The construction of a class of dynamic twirlers is outlined. A special choice for a computationally stable twirler is described by ṙ=p+… and ṗ=F+…+cst (F·p/T) W×p . The new dynamic variable W obeys the equation Ẇ=−(cst/T)F×p, where T is the temperature. The quantity cst is the stirring coupling coefficient which has to be chosen appropriately. The ellipses … stand for terms associated with the standard thermostats and with the influence of a shear flow as treated by the SLLOD algorithm. Results are presented for the isotropic harmonic oscillator and an extendable dumbbell2. Furthermore, the influence of confining walls on the rotation are analysed for the dumbbell.
1) C. Aust, M. Kröger, S. Hess, Macromol. 32 (1999) 5660; 35 (2002) 8621.
2) S. Hess, G.P. Morriss, Physica D (2003) in press.

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