[gmx-users] Re: 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: [gmx-users] Re: long range energy
>Date: Mon, 22 Jan 2007 08:46:52 -0500
>
>
>>Richard Vadnais wrote:
>>>hi all,
>>>
>>>     I want to find four types of energies from my simulation:  LJ and
>>>Coulomb at long and short range. I use PME for coulomb type and cut-off
>>>for VdW type with rlist = rcoulomb = 0.9
>>>
>>>    However, the LJ (LR) and Coulomb LR are not generated in the output
>>>nor can I get them with g_energy.
>>
>>That's because they aren't defined when rlist = rcoulomb. Have a read of
>>the relevant manual sections.
>>
>>Mark
>>
>>
>   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.

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