[gmx-users] Dihedral parameters in Gromos53A6OXY+D

[Patrick Fuchs]

Hi Anjana,
you can add several dihedral functions for the same quadruplet of atoms. 
They will add up when you calculate the potential energy for that dihedral.
As for the 53A6OXY+D, the parameters have been merged recently, together 
with other improvements, into a new set called 2016H66 
(10.1021/acs.jctc.6b00187). You can find the FF files for some liquids 
on the web-page of Philippe Hünenberger 
(http://www.csms.ethz.ch/files_and_links/GROMOS/2016H66.html). 
Alternatively, I also put these parameters on my github web page 
(https://github.com/patrickfuchs/CiEj_2016H66), where there is a copy of 
Philippe's file, as well as the topology for non ionic CiEj surfactants 
(coming from this paper 10.1021/acs.langmuir.7b01348). Since these CiEj 
surfactants have a PEG polar head group, it might be convenient for you 
to start from those. For the time being, those files were tested within 
GROMACS 4 versions, but I plan to add other versions for GROMACS 5 and 
2016 in the near future. I realize it would be convenient to also add 
some PEG topologies there (will try to do that before summer).
Best,

Patrick

Le 10/02/2018 à 11:18, Anjana Jayasinghe a écrit :
> Dear All,
> I am trying to change the parameters for a PEG molecule using OXY+D ( https://pubs.acs.org/doi/abs/10.1021/ct300245h) parameters. When I tried to change the dihedral angles of C-C-O-C and O-C-C-O,  there are three new defined dihedral angles for each mentioned types. But in original 53A6, there is only one dihedral type available for those categories. I'm bit confused with OXY+D dihedral parameters for C-C-O-C and O-C-C-O.
> Appreciate, if anyone can help me.
> Thank you.
>