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Re: [ESPResSo-users] failed to tune P3M paremeters to required accuracy

From: Stefan Kesselheim
Subject: Re: [ESPResSo-users] failed to tune P3M paremeters to required accuracy
Date: Mon, 24 Feb 2014 16:09:24 +0100

Dear Roya,

On Feb 24, 2014, at 4:04 PM, roya moghaddasi <address@hidden> wrote:

> Dear Stefan,
> The bjerrum length is 3.0. When I use 3.0 for bjerrum length in my system the 
> error: bond broken between particle ... occurred. I mailed the mailing list 
> about this problem and they said I should gradually increase the bjerrum 
> length, so I wrote this loop:
> set bj 0.001
> for {set b 1} {$b<3000} {incr b} {
> set bj [expr $bj+0.001]
> puts [inter coulomb $bj p3m tune accuracy $accuracy]
> puts "$bj"
> }

In every increment, you should simulate a bit. This gives the system the chance 
to adjust to the possibly strong electrostatic interactions. By feeling I'd say 
30 increments of 0.1 and 100 MD steps in between could be enough. 

I'm not  sure it is necessary to re-tune p3m always in between, because the 
optimal parameters do not depend on the Bjerrum length. The Bjerrum length is 
only a scaling factor for the error. Doing just
inter coulomb $bj p3m
should, to my knowledge to the job.

Cheers and good luck

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