Reverting to the
notation we introduce an appropriate perturbative term in the Hamiltonian:
(8.23)
where
is the hydrodynamic velocity field, and
(8.24)
(inner product.)
For reasons of his own, W. Hoover dubbed the construct
Doll's tensor.
Written in dummy index notation we have (omitting the particle index )
(8.25)
and the resulting equations of motion are
(8.26)
(8.27)
To avoid gradual heating of the sample, a Gaussian (or other) thermostat
may be added.
For the simple homogeneous shear with
as the only non-vanishing element of
, the
above equations read
(8.28)
(8.29)
(8.30)
(8.31)
(8.32)
(8.33)
Shearing boundary conditions as introduced by Lees and Edwards
may be applied. But now the flow is driven by the additional terms
in the equations of motion.
Again, the stress tensor element is evaluated, and from
its average the viscosity is determined as
.
The method may used with an oscillatory applied shear,
yielding the frequency-dependent viscosity. Also, a volume dilation may
be applied to determine the bulk visosity.
F. J. Vesely / University of Vienna