[gmx-users] Hydroixde Ion

[Justin A. Lemkul]

SHIVANGI NANGIA wrote:
> Hello,
> 
> Thanks a lot for the suggestion.
> 
> I think I made some progress but I am not there yet.
> 
> I added the following in the ions.itp file
> 
> [ moleculetype ]
> ; molname   nrexcl
> OH    1
> 
> [ atoms ]
> ; id  at type  res nr   residu name at name  cg nr charge
> 1  OH 1  OH    OH  1  0
> 1  OW 1  OW    OW  1 -1
> 
> 
> Still I ran into the same error that it could not find moleculetype OH.
> 
> Than I specifically added the following to the .top file
> 
> [ moleculetype ]
> ; molname   nrexcl
> OH    1
> 
> [atoms]
>      1         OH      1   OH     OH      1       0.21     1.008     ;
>      2         OW      1   OH     OW      1      -1.21    15.99994   ;
> [ bonds ]
>    OW   HW1    gb_38
> 
> This helped.
> However, there is new error I am running into which says:
> Fatal error: number of coordinates in coordinate file 
> (5his8_meohi_wat.gro, 12487) does not match topology (topol.top, 12519)
> 
> I am trying to add 8 hydroxide ions in my methanol-water system.
> 

And how are you attempting this?  What command(s) did you give?  What subsequent 
modifications to your topology did you make?

The generic solution to your problem can be found here:

http://www.gromacs.org/Documentation/Errors#Number_of_coordinates_in_coordinate_file_does_not_match_topology

> The confusion I have is:
> The .gro file has OH but is gromacs really accounting OH as 2 atoms? 

Gromacs assigns parameters to the molecules it finds based on the entries in the 
respective [moleculetypes].  If you tell grompp or any other program that the 
[moleculetype] "OH" is comprised of two atoms, then there's no reason to believe 
  anything is wrong.

> Also, the difference (12519-12487) is greater than 8.
> 

Without some context as to what you're doing and what you've done up to this 
point, this information does not lead to any useful solution.  The number of 
molecules (either methanol or OH) in your topology does not match the contents 
of your coordinate file.

-Justin

> Kindly help.
> 
> Thanks,
> Shivangi
> 
> 
> 
> Shivangi Nangia
> Garrison Group
> Graduate Student
> 201A Chemistry Building
> University Park PA 16802
> 
> On 22/03/2011 7:44 AM, SHIVANGI NANGIA wrote:
>  > Hello,
>  >
>  > I am new gromacs user.
>  > I am trying to set up a water-methanol system with few hyrdroxide ions.
>  >
>  > Since hyrdroxide ion does not already exist in gromacs database, I 
> defined the following in the .rtp file ( I am using ffG53a6)
>  >
>  > [ OH ]
>  >  [ atoms ]
>  >    OW    OW    -1.41000     0
>  >   HW1     H     0.41000     0
>  >  [ bonds ]
>  >    OW   HW1    gb_38
>  >  [ angles ]
>  > ;  ai    aj    ak   gromos typpe
>  >  [ impropers ]
>  > ;  ai    aj    ak    al   gromos type
>  >  [ dihedrals ]
>  > ;  ai    aj    ak    al   gromos type
> 
> That's only useful for pdb2gmx when generating .top files.
> 
>  > I also included OH in the .atp file ( I realise that hydroxide ion is 
> NOT an atom, its a diatomic anion, I was just trying!)
> 
> Don't. The .atp defines *atom* types.
> 
>  > I ran into the error: No such moleculetype OH
>  >
>  > I further included information in the ions.itp as follows:
>  >
>  > [ moleculetype ]
>  > ; molname   nrexcl
>  > OH    1
>  >
>  > [ atoms ]
>  > ; id  at type  res nr   residu name at name  cg nr charge
>  > 1  OH 1  OH    OH  1 -1
> 
> Use two atoms, like you did for your .rtp entry.
> 
>  > The genion adds the "OH"  in the .gro file and also the topol.top but 
> when I try to minimize the system using
>  > grompp -f minim.mdp -c 5his8_meohi_wat.gro -p topol.top -o em.tpr
>  > I am still running into the same error, No such moleculetype OH.
> 
> Your .top still does not have a functional [ moleculetype ] OH. You're 
> probably not using the #include "ions.itp"  mechanism correctly.
> 
> Mark
> 

-- 
========================================

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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