[gmx-users] Units within Packaged OPLS Force Field File (ffbonded.itp)

[Matthew Howenstine]

All,

I was just confirming what the units within the
prepackaged \share\top\oplsaa.ff\ffbonded.itp file (within Gromacs version
5.0.7) are - I have seen various sources on the OPLS units, and have mostly
confirmed that most all are already converted to a kJ basis within this
file (i.e. harmonic bond angle force constant [kJ/mol/rad^2],
Ryckaert-Bellemans constants [kJ/mol]). My main question was in the
improper angle's periodic force constant at the bottom -

i.e. in the lines:
; Z -CA-X -Y improper torsion. CA is any ring carbon
(CA,CB,CN,CV,CW,CR,CK,CQ,CS,C*)
#define improper_Z_CA_X_Y 180.0 4.60240 2

Is the 4.60240 in kcal/mol or kJ/mol? I found one OPLS derived force field
file online where a different value was used for the benzene improper
dihedral. Essentially, is there any source which outlines exactly the units
within ffbonded.itp, or do you just have to back-reference the GROMACS user
manual's functional forms as they have already been converted to the proper
form before inclusion within the Gromacs distribution?

Thank you,
Matthew Howenstine

-- 
Matthew Howenstine
University of Notre Dame
Chemical Engineering
mhowenst at nd.edu