Conversion of OPLS ITP file to charmm/gromacs itp file

User discussions
1

greetings users,

I have generated an gromacs compatible ff for a ligand from LIGPargen.
ITP is in OPLS ff format having sections as follows.
; GENERATED BY LigParGen Server
;
[ atomtypes ]
[ moleculetype ]
[ atoms ]
[ bonds ]
[ angles ]
[ dihedrals ]
**; IMPROPER DIHEDRAL ANGLES **
[ dihedrals ]
; PROPER DIHEDRAL ANGLES
[ pairs ]

I want to convert the parameters to gromacs compatible charmm FF. this FF require sections like

CHARMM36 FF in GROMACS format

[ defaults ]
[ atomtypes ]
; name at.num mass charge ptype sigma epsilon ; sigma_14 epsilon_14
** [ bondtypes ]**
[ angletypes ]
; i j k func th0 cth S0 Kub
[ dihedraltypes ]
; i j k l func phi0 cp mult
can someone suggest way to interconvert the parameters?
I will be really thankful for your help.

2

Hi,
just a general comment. Parameters compatible with one force field can not be used with another force fields. One can not mix force fields.
Best regards
Alessandra

3

Dr. alevilla .
thankyou for your suggestion. iam dealing with a rare molecule and it had been a challenge getting forcefields. I was thinking of converting LJ parameters only.

or the other way around, can you please post some server from where i can get POPC bilayer parameters in OPLSAA forcefield?
that would be great.