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Re: [ESPResSo] wall constraint use

From: Kai Grass
Subject: Re: [ESPResSo] wall constraint use
Date: Tue, 5 Feb 2008 09:43:35 +0100

Hi Matthew,

some answers.

A few questions:
1.) Is a normal +1/-1 needed for floor/ceiling distinctions (i.e. is it one sided)?
Yes. Walls are directed, i.e. all particles have to be on one side of it. The side the normal points to.

2.) Is a normal [0 0 1] wall constraint an infinite plane extending through all periodic images?

3.) Why do two normal [0 0 +/-1] wall contstraints at dist z=0 and z=10 in a 10x10x10 box give a constraint violation error for one particle which starts at the center [5 5 5]?
Because the distance to the origin (z) is measured in multiples of the normal, hence you need to put the second wall (top) at z=-10. In fact, I don't know, if it is okay to put the wall directly at the simulation box boundaries at all.

4.) Can the wall constraint be placed (in pairs if necessary) at [5 5 5] in a 10x10x10 box with particles above or below the pair?
No, see 1.

5.) Does the wall constraint work with analyze energy?
I don't know.

6.) Does Partial_Periodic help solve any problems that may arise with the above scenarios?
No, I don't think so.


Thank you,

Matthew Hoopes
Biophysics Graduate Group
University of California, Davis


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Dipl. Phys. Kai Grass
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