[gmx-users] trjorder not working
Justin A. Lemkul
jalemkul at vt.edu
Thu May 5 22:37:11 CEST 2011
shivangi nangia wrote:
> Hello,
>
> Came back to the set of calculations I was doing few days back.
>
> I have a box of water (TIP4P), methanol, protein and DHB anions.
>
> I minimized this system.
>
> Trying to use trjorder for water molecules with respect to the protein
> (eventually I want to make a sphere by ordering and getting rid of the
> molecules I do not want)
>
> In the index.ndx file i specified atom "144" (belongs to protein)
>
> so when I run
>
> trjorder -f em.gro -s em.tpr -n index.ndx -na 4 -o ordered.gro
>
> I pick number associated with atom "144" and SOL ( tip4p water) and I
> generate ordered.gro
>
> The sequence for SOL changes ( random), but when I use g_dist as I go
> down the ordered.gro, there is still no trend ( ascending with respect
> to protein)
>
>
I suspect your index file is wrong. Presumably, you have measured distances to
individual water molecules using g_dist, which would require a custom index
group for each water molecule analyzed, correct? If you use ordered.gro, the
residue numbers will indeed be scrambled based on ordering, but the distance
will correspond to the original distance, not the ordered one.
The solution is to use your unordered coordinate file or .tpr file to create the
index group, then perform the distance measurements. Alternatively, use genconf
to renumber ordered.gro to get sequential residue numbers, then create whatever
index file you might need from the renumbered coordinate file.
>
>
>
> Also, -da 0 refers to an atom OR COM of the molecule.
> using trjorder -f em.gro -s em.tpr -n index.ndx -da 0 -na 4 -o
> ordered.gro and running it
>
> and choosing "1" for protein and "14" for SOL means that gromacs
> automatically understands that protein's COM is to be used to order SOL
> (tip4p, -na 4) ??
>
As the documentation is written, yes.
> If so, then tha talso generates a .gro file which produces random water
> molecules but there is again no trend.
>
Same problem as above, I suspect.
-Justin
> I am very confused about using trjorder, it will be really helpful if
> someone or Mark can help me understand.
>
> Thanks a lot
> SN
>
>
> On Thu, Apr 28, 2011 at 9:43 PM, Mark Abraham <Mark.Abraham at anu.edu.au
> <mailto:Mark.Abraham at anu.edu.au>> wrote:
>
> On 4/29/2011 11:29 AM, shivangi nangia wrote:
>> Hello,
>>
>> The manual explaining trjorder says:
>>
>> trjorder orders molecules according to the smallest distance to
>> atoms in a reference group or on z-coordinate (with option -z).
>> With distance ordering, it will ask for a group of reference atoms
>> and a group of molecules. For each frame of the trajectory the
>> selected molecules will be reordered according to the shortest
>> distance between atom number -da in the molecule and all the atoms
>> in the reference group. *The center of mass of the molecules can
>> be used instead of a reference atom by setting -da to 0*
>>
>> In order to arrange water molecules in accordance with the COM of
>> the polypeptide, I chose -da 0.
>
> As it says above, -da refers to an atom or COM of the molecule, not
> the reference group. This could be worded better in the documentation.
>
> Be sure you're choosing the groups you think you are choosing - you
> not copying relevant parts of your terminal output into emails is
> making things difficult.
>
> Mark
>
>>
>> Am I wrong?
>>
>> Thanks,
>> SN
>>
>>
>>
>>
>> On Thu, Apr 28, 2011 at 8:29 PM, Mark Abraham
>> <Mark.Abraham at anu.edu.au <mailto:Mark.Abraham at anu.edu.au>> wrote:
>>
>> On 4/29/2011 4:08 AM, shivangi nangia wrote:
>>
>> Hello all,
>>
>> I am trying to order the TIP4P water molecules in my
>> system with respect to the polypeptide in my system.
>>
>> The command I am using is:
>>
>> trjorder -f shape.gro -s shape.tpr -da 0 -na 4 -o
>> ordered.gro
>>
>> This runs without any error and ordered.gro is generated
>> with random sequence of water molecules.
>>
>> Just to cross check I calculated the distances between one
>> of atoms of the polypeptide and oxyegn atom of different
>> "ordered" water molecules.
>> I found, there is no ascendig trend in the distances with
>> respect to the polypeptide as a go down in the
>> "ordered.gro" file.
>>
>> What could be going wrong?
>>
>>
>> -da 0 has a particular effect - is it appropriate? Did you
>> choose the right groups? You could use the -nshell option to
>> probe what trjorder thinks is going on.
>>
>> Mark
>>
>>
>>
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>
>
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--
========================================
Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
MILES-IGERT Trainee
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080
http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
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