[gmx-users] OPLS 1-4 interactions & intramolecular contributions to interaction energies ...

[Erik Lindahl]

Hi,

> Can anybody tell me what the proper way of including
> 1-4 non-bonded interactions with the OPLSAA FF is ?
>> From previous messages in this list I gather that
> there seems to be no unique definition and the scaling
> factor for the 1-4 interactions including H-atoms seems
> to be different in different Gromacs versions. What is
> this factor in 3.2.1, what is it in 3.1.4 and which is the
> "correct" one ?

The scaling factors are defined in the force field files and not 
hardcoded. They have always been 0.5 for both charge and LJ in OPLS-AA, 
but other forcefields obviously have different serttings.

For OPLS-AA you should include 1,4 interactions between hydrogen atoms, 
while many other forcefields prescribe you shouldn't (e.g. Gromos96). 
This is controlled with a standard flag to pdb2gmx, but the default 
value is set in the rtp file for the last couple of gromacs versions.


Cheers,

Erik