[gmx-users] nonbond_params

[Justin A. Lemkul]

The [ nonbond_params ] section is located in the nb.itp file of your chosen 
force field.  The error comes from the fact that you have likely tried to 
introduce an additional [ nonbond_params ] directive within your .top file, 
which is incorrect.  You cannot have multiple entries for these directives, and 
they must follow a certain order (given somewhere in the manual).

To introduce the additional atom type, you'll need to edit the nb.itp and .atp 
file for your force field to account for the new atom type.

-Justin

Amir Marcovitz wrote:
> Thank you Justin,
> 
> I didn't understand though where can I edit the [ nonbond params ] section?
> Is there a better way to define pairs with no LJ attraction that will 
> ignore the settings in the *nb.itp file?
> 
> Cheers,
> Amir
> 
> On Mon, Jul 26, 2010 at 5:31 PM, Justin A. Lemkul <jalemkul at vt.edu 
> <mailto:jalemkul at vt.edu>> wrote:
> 
> 
> 
>     Amir Marcovitz wrote:
> 
>         Hi,
> 
>         my system is composed of two molecules, each is composed of a 36
>         carbon like dummy atoms i defined in the amber files (i.e., has
>         the LJ parameters of a carbon)
>         I'm interested in eliminating the attractive Lennard-Jones
>         interactions between the dummy atoms , such that only the
>         repulsive terms will account.
> 
>         I thought of adding a section to the *.top file:   [ nonbond
>         params ] and to set c6 to 0 such that the attractive term of the
>         LJ is eliminated.
>         I used exactly the same syntax of the tutorial (page 98):
>              * D     D        1       0.00000E-00       0.34252E-05*    
>          ; (D is just the name of my dummy atom)
> 
>         but got a syntax error when running grompp:
>         *Fatal error:
>         Syntax error - File Surface_Surface_1.5_Sep_2.5.top, line 642
>         Last line read:
>         '[ nonbond_params ]'
>         Invalid order for directive nonbond_params*
> 
>         1) what is wrong with my syntax? are there any further examples
>         anywhere for the usage of  [ nonbond params ] in topology files?
> 
> 
>     If you have already #included a force field file in the .top, it
>     will have a [nonbond_params] section in it already.  You cannot add
>     a new one.  The proper approach would be to modify the #included
>     *nb.itp file.
> 
> 
>         2) Is [ nonbond params ] the right strategy to the task i described?
> 
> 
>     Sounds like one way to do it.
> 
>     -Justin
> 
>         Many Thanks,
>         Amir
>          
>          
> 
> 
>     -- 
>     ========================================
> 
>     Justin A. Lemkul
>     Ph.D. Candidate
>     ICTAS Doctoral Scholar
>     MILES-IGERT Trainee
>     Department of Biochemistry
>     Virginia Tech
>     Blacksburg, VA
>     jalemkul[at]vt.edu <http://vt.edu> | (540) 231-9080
>     http://www.bevanlab.biochem.vt.edu/Pages/Personal/justin
> 
>     ========================================
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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

========================================