Re: [ESPResSo] PSAW

[Axel Arnold]

On Tuesday 26 October 2010 21:20:50 Mikheil Azatov wrote:
> Hi!
>
> Yes I was talking about he polymer command.  The differences probably
> appear only in the equilibration part. I mean in the beginning of the
> simulation I had the maximum distances between particles in the polymer
> larger then when using SAW. The User Guide says just that statistics for
> PSAW is different then a statistics for SAW but it doesn't say in what way
> are they
> different.

If a monomer of the PSAW cannot be placed, this monomer will be simply put to 
another position, while the SAW discards the whole polymer and starts again. 
Therefore, PSAW is much faster, but the statistics is slightly biased, since a 
blocked move increases the probability for the possible moves around. At low 
concentrations, the effect is low and can probably be healed by equilibration, 
but at high densities, the entanglement won't have SAW statistics, although I 
don't know which statistics it will have.

> I also wanted to ask if constraints are walking for RW polymers. I usually
> create polymers with constraint command because i want them to be in a
> certain volume. After I create polymers I delete constraints. When I use
> PSAW and SAW commands for polymers everything works fine and the polymers
> are being created within that volume. For RW it doesn't work that way. The
> polymers are kind of "reflected" from the borders of constraints and can
> have other ends on the other side of the simulation box. I think sometime
> they even "merge" with each other( particles with different ID's that
> belong to different polymers are actually same particles). I don't use PBC
> and the output to vmd are unfolded coordinates, so i don't think it's
> connected to it. So i was wondering if constraints are actually working
> with RW and I'm just doing something wrong or they just don't work with RW
> polymers?

No idea, there is only one code for generating a polymer (polymer.c:polymerC) 
which is used for SAW, PSAW and RW. Therefore, if the first two work with 
constraints, also the last should. If you can send us a script that reproduces 
your problem, we can take a look.

Axel

-- 
JP Dr. Axel Arnold Tel: +49 711 685 67609
ICP, Universität Stuttgart      Email: address@hidden
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70569 Stuttgart, Germany