[gmx-users] need help with topology file

[Justin A. Lemkul]

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

-- 
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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

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