[gmx-users] Creating topology file for TBA cation using OPLS force field

[Mark Abraham]

Andrey A. Koverga wrote:
>    Hi all! I'm just a beginner user of Gromacs, that's why my question 
> may seem strange to you. But I hope, that somebody can help me in 
> solving my problem. The point is that I'm trying to perform the analysis 
> of tetrabutylammonium cation solvatation using OPLS force field. Earlier 
> i've modelled tetrametylammonium cation with same force field; the 
> topology *.itp file for TMA was created, using The Dundee PRODRG Server: 
> itp-file was created for some Gromacs force field, and than modified by 
> definition of the UA-groups according to OPLS UA-types. This way is 
> unsuitable for determination of TBA topology, 'couse in this case 
> "all-atom" determination should be performed. So that's why I'm asking 
> your advise what should I do. Thanks a lot!

Read how OPLS was parameterized and do something consistent with that. 
Anything else is random number generation (and even this might be!)

Mark