[gmx-developers] Define an new group

[Berk Hess]

Hi,

Acceleration groups will not work as those add an extra force to a group 
and do not keep the total acceleration constant.

I think that using a pull coordinate with absolute reference and of 
constraint type should work, then you need to set a velocity using the 
free-energy coupling with lambda and setting a pull rate.

Otherwise you can indeed use one of the two user groups.

Cheers,

Berk

On 2020-04-10 13:01, Erik Lindahl wrote:
> Hi Rebecca,
>
> I have to confess it was a _long_ time since I looked into these parts 
> of the code, but you might be able to achieve this simply by defining 
> a group, giving it the initial velocity you want, and then using the 
> constant-acceleration functionality with the value 0.0 (since zero 
> constant acceleration means constant speed).
>
> And if that fails, it should be possible to fix it without too much 
> effort :-)
>
> Otherwise, the idea of the user groups is exactly that you should be 
> able to quickly implement a small routine where you do something to an 
> arbitrary group without having to redefine the input mdp options, 
> create a new (incompatible) TPR version, and also having to modify the 
> enum lists.
>
> Cheers,
>
> Erik
>
> On Fri, Apr 10, 2020 at 12:55 PM Rebecca Kleemann 
> <rkleeman at students.uni-mainz.de 
> <mailto:rkleeman at students.uni-mainz.de>> wrote:
>
>     Hi,
>
>     I want to add a group to set atoms to a constant velocity.
>
>         enum
>         {
>             egcTC,    egcENER,   egcACC, egcFREEZE,
>             egcUser1, egcUser2,  egcVCM, egcCompressedX,
>             egcORFIT, egcQMMM,
>             egcNR
>         };
>
>         const char *gtypes[egcNR+1] = {
>             "T-Coupling", "Energy Mon.", "Acceleration", "Freeze",
>             "User1", "User2", "VCM", "Compressed X", "Or. Res. Fit",
>         "QMMM", nullptr
>         };
>
>     Are "User1" and "User2" meant to be used like that and can they be
>     renamed or should I add a new group and increase the number of groups?
>
>     Greetings,
>
>     Rebecca
>
>     -- 
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> -- 
> Erik Lindahl <erik.lindahl at dbb.su.se <mailto:erik.lindahl at dbb.su.se>>
> Professor of Biophysics, Dept. Biochemistry & Biophysics, Stockholm 
> University
> Science for Life Laboratory, Box 1031, 17121 Solna, Sweden
>

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