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Re: [ESPResSo-users] How to adjust reflecting constraints in version 4.0
Re: [ESPResSo-users] How to adjust reflecting constraints in version 4.0.1
Mon, 18 Feb 2019 14:55:50 +0100
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The feature was removed due to bugs and energy conservation issues. A
brief discussion can be found in these two threads:
I am unaware of any plan to re-implement a fixed version of this feature
in the short term. You could probably achieve the desired effect with an
LJ potential between the shape and particles, using a small sigma to
limit the "curving" of trajectories near the shape surface, and using
cutoff=sigma to only get the repulsive part of LJ (this is basically
what the WCA potential does, which can be enabled during compilation).
The reason we couldn't find the keywords "reflection" and "reflecting"
in the documentation is that the url you provided points to an old page
which is not referenced by the Sphinx search engine anymore. This page
should have been erased a year ago. We apologize for the inconvenience.
I'll open a ticket to clear the docs from outdated files.
On 2/18/19 10:29 AM, address@hidden wrote:
Thanks for your answer!
Exactly, what I'm looking for is such a reflect_particle() function
like the one mentioned by you within shaope based constraints.
In the docs it is mentioned at
under point 4.10.1:
"In variants wall; sphere; cylinder; rhomboid and stomacyte it is also
specify a flag indicating if the constraints should be reflecting. The
flags can equal
1 or 2. The flag 1 corresponds to a reflection process where the
of the velocity is reflected and the tangential component remains
unchanged. If the
flag is 2, also the tangential component is turned around, so that a
motion is performed. The second variant is useful for boundaries of DPD.
property is only activated if an interaction is defined between a
particular particle and
the constraint! This will usually be a lennard-jones interaction with
ϵ=0, but finite interaction
So what I'm trying to do is to implement a cylindrical (shape based)
constraint in which the particles are
reflected by the constraint as described above.
However, I haven't found a way to specify a flag as indicated above for
shape based constraints.
How would you use the reflect_particle() function which you mentioned?
Zitat von David Sean <address@hidden>:
I am trying to understand what you mean by 'reflecting'. I tried
searching the docs for 'reflect' but could not find it mentioned in
the context of a constraint. Constraints are described here:
http://espressomd.org/html/doc/constraints.html and there is a sample
script /samples/constraints.py that you can look at.
There used to be a reflect_particle() function for shape-based
constraints, did you mean that? Can you describe what you are trying
do, i.e, is this for particles, or an LB fluid... or both?
Le mer. 13 févr. 2019 à 08:07, <address@hidden> a
In my simulation with ESPResSO 4.0.1 I'm trying to implement a
cylindrical constraint which should be reflecting.
I saw in the docs that this should be possible for the variants wall,
sphere, cylinder, rhomboid and stomacyte.
However, it seems there is no option to include the reflecting flag,
either to "espressomd.shapes.Cylinder" nor to
"espressomd.constraints.ShapeBasedConstraint". In both cases I receive
a "unknown parameter"-error.
Can anyone help me here and explain where to specify the flag?
I also have an activated Lennard-Jones interaction defined between the
particles and the constraint.
I would really appreciate your help.