Dresden 2003 – wissenschaftliches Programm
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DY: Dynamik und Statistische Physik
DY 20: Soft matter I
DY 20.2: Vortrag
Dienstag, 25. März 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.