Hi,
(Could you send me some coordinates to go along with that topology file?)
On Mon, Jul 10, 2017 at 12:15 PM, Guqin Shi <shi.293.osu.edu> wrote:
> at the bottom edge of box......According to the original prmtop files, the
> complex sits at the center of water box, but also meantime, it sits along
> the diagonal line...It seems center-image puts molecule along any of the
> side line and that's why it just couldn't fit all back...? But I am so
> confused now as why early trajectories could be imaged without any
> problem...
Re-imaging is more of an art than a science, mostly because imaging is
something that we do to make things "look nice". The molecules being
simulated don't care where they are absolutely, they only care where
they are with respect to other molecules. When you center on one
molecule, you shift the coordinates of the entire system, some of
which move past the boundaries of your unit cell. Those atoms are then
"wrapped" or re-imaged back inside the unit cell, which is what can
result in molecules appearing "separated". The 'autoimage' command
tries to image in a way that keeps these molecules together by
defining an anchor molecule/region (which is at the center), and
molecules that are "fixed" to that anchor - it then tries to minimize
the distance between the anchor and fixed molecules. Where this fails
is when a "wrapped" version of the system has shorter distances than
the "unwrapped version", which is typically because the definition of
the anchor (center) is off. This is why the definition of the "anchor"
region is so crucial.
Send me those coordinates and I'll see what can be done.
-Dan
>
>
> Thanks,
> Guqin
>
> On Mon, Jul 10, 2017 at 11:43 AM, Guqin Shi <gshi.cop.ufl.edu> wrote:
>
>>
>> On Mon, Jul 10, 2017 at 8:32 AM, Daniel Roe <daniel.r.roe.gmail.com>
>> wrote:
>>
>>> Hi,
>>>
>>> The key for 'autoimage' is that you need to specify a region
>>> (molecule, residue, atom, etc) that visually you want to be at the
>>> center of your unit cell; in cpptraj this is called the 'anchor'. By
>>> default 'autoimage' tries to use the first molecule to do this.
>>> However in certain systems another choice is better. For example, if
>>> you have a dimer then you would want to choose 1 or more residues that
>>> are near the center of the interface between the two monomers as your
>>> anchor. Without seeing your system I can't make specific
>>> recommendations, but you could try experimenting with different anchor
>>> points. If you'd like, send me a PDB file or topology/restart files of
>>> your system off-list and I can try to recommend an anchor.
>>>
>>> -Dan
>>>
>>>
>> Hi Bill,
>>
>> Thanks for pointing out the key point of "autoimage". I tried to play with
>> autoimage-anchor a little bit by myself. I noticed that the mask for
>> autoimage are molecule-wise, instead of residue-wise... Therefore when I
>> specify some center residues, cpptraj reports back with error (Error:
>> Anchor mask [:153-155] corresponds to 0 mols, should only be 1.) and then
>> it goes with default again... Maybe my syntax is somehow not correct?
>>
>> Also, my system is a little bit special. It is a "dimer" and each monomer
>> contains three molecules. There is a hollow in between the two dimers...
>> Currently in my own practice, I picked three residues on each of the dimer
>> which I think, are the closest to the center of cell (143-155 & 818-820).
>> Also, since these residues are symmetric, I am not sure how the program
>> would place them in terms of direction...or maybe in this case, asymmetric
>> residues might be better...? I attached the prmtop file (with solvens/ions)
>> here on my google drive:
>> https://drive.google.com/open?id=0B7kncIsWo85ud1BweGJfd1h1ZXM (Since it
>> is quite big so I don't think mailing list server would allow that size..)
>> Could you also check my system to see if my choice on residues are good or
>> maybe another set of residues are better..?
>>
>>
>> Thanks a lot for your help!
>> -Guqin
>>
>> --
>> Guqin SHI
>> 1345 Center Drive
>> College of Pharmacy
>> PO Box 100485
>> University of Florida
>> Gainesville, FL 32610
>>
>
>
>
> --
> Guqin SHI
> PhD Candidate in Medicinal Chemistry and Pharmacognosy
> College of Pharmacy
> The Ohio State University
> Columbus, OH, 43210
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--
-------------------------
Daniel R. Roe
Laboratory of Computational Biology
National Institutes of Health, NHLBI
5635 Fishers Ln, Rm T900
Rockville MD, 20852
https://www.lobos.nih.gov/lcb
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Received on Mon Jul 10 2017 - 09:30:04 PDT
