Re: [ESPResSo] constraints and nemd

[Jens Smiatek]

Dear Guillaume,

1.) Negative values for the plane cell command indicate zero spatial 
dimension. The value of -10 is chosen arbitrarily.
For example:
constraint plane cell -1 5 -7 type id
indicates an infinite wall at y=5 sigma position with no components in x 
and z-direction.
The reason for that usage is the possibility to model structured 
microchannels.
Your examples:
For x1,2 and y1,2 use negative chosen arbitrary values like -1,-2,-3,...
The problem:
Make sure that all particles are inside the channel confined between both 
two walls and outside the 
cutoff-range of the LJ-potential. Otherwise you'll receive error mesaages 
like 063.
2.) The tunable-slip boundaries can only be used with the constraint cell 
command. 
3.) The viscosity can be calculated by a Plane Poiseuille flow and the 
tunable-slip boundaries method. Check the corresponding literature at the 
end of the paragraph of the ug.

Best regards,
Jens

==========================================
Jens Smiatek

Institute of Physical Chemistry
Room E0-002
Tel.: 0049-251-83-29154
email: address@hidden

Institut fuer Physikalische Chemie
Corrensstrasse 28/30
D-48419 Muenster
Germany
==========================================

On Thu, 25 Mar 2010, Guillaume Larsen wrote:

> 
> dear all,
> 
> i have several questions concerning the 'constraint plane cell' feature:
> 1) the definition of this constraint doesn't seem really clear to me, 
> 'constraint plane cell x y z type id'
> the example from the manual:
> create an in???nite plane in z -direction at z = 20.0 of type id 1, use: 
> constraint plane cell -10 -10 20 type 1
> to define a plane, one should need a normal vector and a position from 
> origin, but here we only have 3 parameters x, y and z to configure. What do 
> represent the '-10' for x and y in the command.
> I want to define two planes: which values for x1,2 and y1,2 should I use to 
> define the planes below?
>     constraint plane cell $x1 $y1 $box_l_i type $wall_type ---> normal 
> z-direction at z=$box_l_i
>     constraint plane cell $x2 $y2 0 type $wall_type ---> normal z-direction 
> at z=0
> So far, i picked different values for x and y, but ESPResSo returns error 
> messages about plane constraint violation (error 063) at warm up phase.
> 
> 2)is it possible to use the tunable slip interaction command associated to a 
> 'constraint wall' command?
> 
> 3)I have been having problems recently with the use of the nemd feature, and 
> i think the misuse of 'constraint plane cell' is the reason. The fact is that 
> I want to use the nemd feature to compute the viscosity of the system. Two 
> 'constraint plane cell' have to be defined before using the command 'nemd 
> viscosity', is it right?
> 
> Thank you in advance for your answers!
> 
> best regards,
> 
> Guillaume
>                                         
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