Re: [ESPResSo-users] How to adjust reflecting constraints in version 4.0.1

[Geiseld]

Hi,

ah, ok. Thanks for the update and the idea. I'll try the WCA potential.

Best regards,
David.

Zitat von Jean-Noël Grad <address@hidden>:

> Hi,
>
> The feature was removed due to bugs and energy conservation issues.  
> A brief discussion can be found in these two threads:
> https://github.com/espressomd/espresso/pull/1952#issuecomment-395213683
> https://github.com/espressomd/espresso/pull/2010
> 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 docs from outdated files.
>
> Best regards,
> JN
>
> On 2/18/19 10:29 AM, address@hidden wrote:
> > Hey David!
> >
> > 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
> >
> > http://espressomd.org/html/doc/inter.html
> >
> > under point 4.10.1:
> >
> > "In variants wall; sphere; cylinder; rhomboid and stomacyte it is  
> > also possible to
> > 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  
> > normal component
> > 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 bounce back
> > motion is performed. The second variant is useful for boundaries of  
> > DPD. The reflection
> > 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
> > range."
> >
> > 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?
> >
> > Best regards,
> > David.
> >
> >
> >
> >
> > Zitat von David Sean <address@hidden>:
> >
> > > Hi David,
> > >
> > > 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?
> > >
> > > David
> > >
> > > Le mer. 13 févr. 2019 à 08:07, <address@hidden> a écrit :
> > > > Hello everybody!
> > > >
> > > > 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.
> > > >
> > > > Best regards,
> > > > David.