[gmx-users] Are the constraint forces included inthe forcesoutputed in the

[Berk Hess]

>From: David van der Spoel <spoel at xray.bmc.uu.se>
>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>Subject: Re: [gmx-users] Are the constraint forces included 
>inthe	forcesoutputed in the
>Date: Fri, 05 Jan 2007 10:40:18 +0100
>
>Berk Hess wrote:
>>
>>
>>
>>>From: "Pu Liu" <puliu45 at hotmail.com>
>>>Reply-To: Discussion list for GROMACS users <gmx-users at gromacs.org>
>>>To: gmx-users at gromacs.org
>>>Subject: [gmx-users] Are the constraint forces included in the 
>>>forcesoutputed in the trr file? Date: Fri, 05 Jan 2007 00:34:03 +0000
>>>
>>>Dear GROMACS list members,
>>>
>>>   Could you please tell me if the constraint forces are included in the 
>>>forces outputed in the trr file, or just used to propagate the system?
>>
>>Constraint forces are not included.
>>
>>We should state this somewhere in the manual.
>>
>>Berk.
>>
>
>I wondered about this before as well. Shouldn't we include them anyway?
>It is quite important when you use the forces for e.g. computing a

You don't want to compute PMF from the forces in the trr file.
You need a lot of sampling for a PMF and the trr would become far
to big.
Currently we have the pull code and free energy code, both with
umbrella sampling and constraints for determining PMF's.

I prefer to have F=-grad V in the trr file and not the constraint forces.

Berk.

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