[gmx-users] need help with topology file

Justin A. Lemkul jalemkul at vt.edu
Thu Jul 28 21:39:36 CEST 2011

jampani srinivas wrote:
> Hi,
> I am trying to use two types of force fields for my system which has 
> protein and fullerene. i want to use OPLS for protein and ffG53a6 for 
> fullerene(as i don't have opls readily available for this). When i use 
> two itp files in #include section grompp does not allow me to do that 
> with the following error. 
> -------------------------------------------------------
> Program grompp, VERSION 4.0.5
> Source code file: topio.c, line: 430
> Fatal error:
> Syntax error - File ffG53a6.itp, line 6
> Last line read:
> '  1 1 no 1.0 1.0'
> Found a second defaults directive.
> -------------------------------------------------------
> Chapter 5 in manual has information about using topology files but i am 
> not clear about using #define. Can anybody help me how to use opls for 
> protein and gromos for fullerene in the same system? 

That will be a meaningless combination.  The force fields use completely 
different combination rules (and hence why you're getting the fatal error about 
trying to use two different [defaults] sections) and are based on different 
parameterization strategies.  You need a self-consistent model and any attempt 
to combine force fields in this way will not succeed.



Justin A. Lemkul
Ph.D. Candidate
ICTAS Doctoral Scholar
Department of Biochemistry
Virginia Tech
Blacksburg, VA
jalemkul[at]vt.edu | (540) 231-9080


More information about the gromacs.org_gmx-users mailing list