[gmx-users] Making easy position restrain

[Hector Mrz-Seara Monne]

Thanks a lot, it has clarify my problem now everything works, but know I 
have problems with  a steep of 3fs that without restrains wasn't 
present, the system crash after a 1,5 ps. This is normal?

Thanks Hector

x.periole at chem.rug.nl wrote:

> Hector Martinez-Seara Monne wrote:
>
>> Hi all,
>> sorry in advance for the question because I'm sure it's not the first 
>> time that has been posted but I haven't been able to find it (also 
>> the manual gives a short example but not enough for allow me to 
>> completely understand how to use it). I just want to know if there's 
>> any easy way to define positions restrains over all the atoms of a 
>> type instead to number all one by one. If yes can you tell me how?. 
>> For example imagine I have a box of SPC water and I want to fix all 
>> oxygens ( this is very related with one of the questions I've read 
>> today) or I want to fix all the heads of a monolayer in a plane 
>> during the equilibration
>>
> From the way position restraint work you have to give a posre.itp file 
> to grompp. This file has to contain
> the list of the atom (number) that you want to apply the restrain on 
> and its index number. The fact is that
> the restrains have to defined for each molecule type. In the case of 
> the water exemple the posre.itp would
> contain the index number of oxygen (3) and the x, y and z restrain 
> force (1000 1000 1000 by default).
>
> You have to define an index (make_ndx) containing the atoms (type if 
> you wish) that will feel the restrain
> and give it to genpr -conf.gro -n index to generate the posre.itp 
> corresponding to the given molecule. Remember
> that you do not define the position restain based on the conf.gro but 
> on the topology of each molecule.
>
> Best
> XAvier
>

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