Units for dihedral force constants in the CHARMM itp file

User discussions
1

GROMACS version:
GROMACS modification: Yes/No

Does anyone know what the units are for the dihedral force constants in the CHARMM itp file?

2

Hi,
GROMACS uses the following unit (Definitions and Units — GROMACS 2021 documentation).
The unit for the dihedral force constants are independent from the force field. In the link below you find the unit for bond, angle and dihedral constant:
File formats — GROMACS 2021 documentation
Usually for dihedrals K is (kJ mol−1) except for improper dihedrals that is kJ mol−1rad−2)

best regards
Alessandra

3

Thanks @alevilla !