[gmx-developers] pull vec

[Berk Hess]

The two groups are connected by a spring (or something like a stiff rod
in case of constraint pulling).
The spring can be along the vector connecting the two groups
(geometry=distance),
or a vector you provide (geometry=direction).
Pair-wise Forces, including pull forces, always work between two (groups
of) atoms.
On atom or group always feels the same force as the other atom or group
involved,
but with opposite direction, as for instance for a LJ or Coulomb
interaction.

Berk

Alexander Herz wrote:
> Ok, so it seams I don't fully understand how the pulling works.
> In which (physical) sense are the two pull groups connected?
>
> Alex
>
> Berk Hess schrieb:
>   
>> Hi,
>>
>> I don't understand what you want to do.
>>
>> You can just specify a single pull vector and the groups will always
>> be pulled in opposite directions (action=reaction).
>>
>> Berk
>>
>> Alexander Herz wrote:
>>   
>>     
>>> Hi,
>>>
>>> In gromacs 3.3 it was possible to define 2 pull groups and pull them in
>>> opposite directions (using afm and 2 dir vecs).
>>> Now I'm trying to run the same sim in 4.0.5. Here I can only specify a
>>> pull_vec1 (pull_vec0 is not parsed as can be seen
>>> in readpull.c "if (i > 0) {"). Is this the intended behaviour? If yes,
>>> how can I specify the pull direction for pull group 0??
>>>
>>> Thx,
>>> Alex
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