GROMACS version: 2019.6
GROMACS modification: None that I am aware of
I would like to simulate a binary system with two diffrent force fields, one of them OPLS-aa and one is refrigerant specific. Both force fields use diffrent scaling factors for the electrostatic 1-4 interactions, 0.5 for OPLS-aa and 0.833 for the other. Up until now I could go with the default section to specify the fudge parameters, but in this case I think I need to specify the pair interactions seperatly.
Now I would like to know if my approach is correct:
Using the [defaults] section to set the default 1-4 interactions to
fudgeLJ = 0.5
fudgeQQ = 0.5
gen-pairs = yes
Using the [moleculetype] section to specify
nrexcl = 3
Using for the OPLS molecules the [pair] section to define the pairs via the numbers of the atoms for which the 1-4 interactions are calculated. For example:
Using the [pair] section of the non-OPLS molecules to overwrite the default 1-4 interactions via funtion 2.
[ pairs ]
4 6 2 0.5 0.20473 -0.18254 2.78E-01 1.25E-01
where 4 and 6 are the numbers of the atoms, 2 is the type of the function, 0.5 the FudgeQQ parameter followed by the partial charges of the atoms 4 (0.20473) and 6 (-0.18254) and the via the combination rule calculated Lennard Jones parameters sigma (2.78E-01) and epsilon (1.25E-01) between those two
From my understanding of the manual this setup should set the default pair interactions to the OPLS settings and then overwrite them for the non-OPLS molecule with the specified pair section.
Did I understand that correctly?
Also, in this situation do I need to specify the pairs of the OPLS molecule or is it enough to set the genpair option to yes?
Thank you a lot for your time!