[gmx-users] molecule index

Jamie Seyed jamie.seyed at gmail.com
Mon Sep 21 02:29:43 CEST 2009


Yes Thanks Justin, should I just use the linear part of msd for fit even if
it is short (like 14ps from 200ps)? Thanks/Jamie

On Sun, Sep 20, 2009 at 8:02 PM, Justin A. Lemkul <jalemkul at vt.edu> wrote:

>
>
> Jamie Seyed wrote:
>
>> Thanks Mark,
>> here are the links.
>> http://www.psc.edu/general/software/packages/gromacs/online/water.html
>>  http://www.mail-archive.com/gmx-users@gromacs.org/msg07653.html
>>  I tried your advice with 1 water molecule and since it worked I tried it
>> with SOL.ndx, but I got
>> D[SOL] -0.0333(+/- 0.0370) 1e-5 cm^2/s
>> It seems not reasonable to me (negative and its error is bigger than
>> itself). Any idea?
>>
>
> Probably inadequate sampling, either from the number of frames saved, or
> from the length of the simulation itself.
>
> -Justin
>
> Thanks in Advance/Jamie
>>
>>
>> On Sun, Sep 20, 2009 at 7:02 PM, Mark Abraham <Mark.Abraham at anu.edu.au<mailto:
>> Mark.Abraham at anu.edu.au>> wrote:
>>
>>    Jamie Seyed wrote:
>>
>>        Hi Mark,
>>        Thanks for the puzzling answer. I tried the index file counting
>>        the number of water molecule but I got an error.
>>        "Fatal error:
>>        The index group does not consist of whole molecules"
>>
>>
>>    OK so apparently it wants atom indices for whole molecules. That
>>    seems much more plausible to me than David's advice you quoted
>>    (please give URLs to such quotes in future, perhaps you took it out
>>    of context...)
>>
>>    So try giving it atom indices for a whole water molecule as an
>>    experiment. Seems like an obvious try to me :-) Then, scale it up if
>>    it seems to work.
>>
>>
>>        I also did not understand what you pointed out about "One of
>>        these sets of numbers is larger than the other" ...
>>
>>
>>    One of the set of atom indices in a protein and the set of molecule
>>    indices in a solvated protein will have more members than the other.
>>    Instead of asking which is right, you might try out a case that will
>>    fail under one assumption and work under the other :-) Then perhaps
>>    ask a question with some evidence behind it.
>>
>>
>>        questions:
>>        1) for msd calculation for water molecules, do I need really
>>        make index file for all waters,
>>        2) What I made (count the water molecules in a [mymolecules]
>>        index file), did not work. How I suppose to do make that?
>>        3) In getting started-Water page that I found in google it only
>>        say "g_msd -n index" and did not explain which index... how
>>        about if I use oxygen.ndx file??
>>
>>
>>    Provide links, please. We're not going to duplicate your googling.
>>
>>    Mark
>>
>>        I really appreciate your help. Many Thanks in Advance/Jamie
>>
>>
>>
>>         On Sun, Sep 20, 2009 at 3:33 PM, Mark Abraham
>>        <Mark.Abraham at anu.edu.au <mailto:Mark.Abraham at anu.edu.au>
>>        <mailto:Mark.Abraham at anu.edu.au
>>        <mailto:Mark.Abraham at anu.edu.au>>> wrote:
>>
>>           Jamie Seyed wrote:
>>
>>               Dear all,
>>               I want to calculate the msd using g_msd. I have a
>>        macromolecule
>>               and some (let say 100) water molecules and I want to use
>>        msd for
>>               water only. from the manual and list I think I need to
>>        make an
>>               index for molecules (water) and use -mol option.
>>                From David's answer on the list I found
>>               -----------------------------------------------------
>>               "If you know which molecules they are then you just write
>>        in a
>>               text editor:
>>               [ mymolecules ]
>>               3 5 19 23 45 109"
>>               ----------------------------------------------------
>>               My question is: let say the macromolecule is coming first
>>        in the
>>               pdb file and then there are water molecules. If I want to
>>        make
>>               an index for only waters, according to this advice, should I
>>               write 2 3 4... 100  (just remove 1 that goes for
>>        macromolecule)
>>               I am wondering if there is a confliction between these
>>               numbers(refer to molecules) and atom numbers of
>>               macromolecule.... Would you please clarify this for me??
>>
>>
>>           Try it and see. One of these sets of numbers is larger than the
>>           other, and if you use a number in that interval you'll either
>>        get an
>>           error or success, either of which will answer your question.
>>
>>           Mark
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>
> --
> ========================================
>
> Justin A. Lemkul
> Ph.D. Candidate
> ICTAS Doctoral Scholar
> 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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