[gmx-users] Question about embedding a force field with no torsion term

[Mark Abraham]

Bo Zhou wrote:
> Hi all,
> 
>  
> 
> Recently I want to embed a force field (/ Chem. Mater.,/ *17* (23), 5658 
> -5669, 2005) in gmx. In the paper, It is said that the force field 
> parameters are consistent with GROMACS. The energy expression has a form 
> as follows:
> 
>             E= E(bond) + E(angle) + E(coulomb) + E(vdW)
> 
>  
> 
> Note that there is no torsion term, I write an itp file manually and use 
> “nrexcel   2” in my molecule. I am not sure about how to deal with the 
> 1-4 interactions, because when I include with the opls force field, gmx 
> still generates 1-4 interactions. Is it necessary for having 1-4 
> interactions here? If necessary, how to make that force field consistent 
> with opls ff ?

You can make it do what you want. See chapters 4 & 5 of the manual.

Mark