[gmx-users] long range energy

[Berk Hess]

>From: "Richard Vadnais" <Richard.Vadnais at usherbrooke.ca>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: <gmx-users at gromacs.org>
>Subject: Re: [gmx-users] long range energy
>Date: Mon, 22 Jan 2007 14:45:30 -0500
>
>
>>   I read these sections and this is where I am confused. It is specified
>>that PME cannot be used with rlilst different than rcoulomb but that if
>>they are egal, long range energies would not be defined. However, I am
>>trying to reproduce a simulation done by a former member of our research
>>group and from the input files (.mdp) he used, I found that he used:
>>
>>rlist = 1.05
>>rcoulomb 1.15
>>coulombtype = PME
>>
>>    From what I gathered from the manual, this combinaison is not 
>>possible,
>>however, not only did he get results from this input, but he had the four
>>types of energies: LJ-(SR), LJ-(LR), coulomb-(SR), coulomb-(LR).
>>   (I should have been more precise in my first post. I apologies.)
>
>You must be using an older version of Gromacs then.
>In 3.3.1 I have added a check on this in grompp.
>
>So now you have the PP (particle-particle) part of PME below
>rlist in Coulomb-SR, the PP part of PME above rlist (updated only
>every nstlist steps) in Coulomb-LR and, if your version is not too old,
>the reciprocal space contribution in Coul.-recip.
>
>Berk.
>
>------
>   Having corrected my entry file, I found LJ-(SR), LJ-(LR), coulomb-(SR) 
>and Coul.-recip. I still don't have the Coulomb-LR though. (I am running 
>version 3.3.1 of gromacs, with nstlist=10) Is Coul.-recip equal to the 
>Coulomb-LR? Is it simply that it changed names?

With "now" I meant in your run with the older Gromacs version,
or to be more precise, with a tpr file made with an older version
of grompp. You can still run such an old tpr file with the twin-range
cut-off with PME with a 3.3.1 mdrun.

The Coulomb reciprocal space used to be stored in Coulomb-LR
in much older Gromacs versions. Since some years the reciprocal
space contribution is stored in Coul.-recip.
I think that in such much older versions with twin-range with PME
both the long-range particle-particle contributions and
the reciprocal space contribution were stored in Coulomb-LR.
But maybe it could have been that one contribution overwrote
the other.

Berk.

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