[gmx-users] puzzling about ffnonbonded.itp

[Wu Chaofu]

Dear gmxers,
While I try to make one customed force field by studying some existing
force fields, I find that bond_type and at.num defining [atomtypes ]
in the ffnonbonded.itp are included in some force fields (i.e.
oplsaa), but not in other force fields (i.e gmx). I wonder how gmx
identifies the difference and choose the correct parameters from them.
Could you please expain this in details? Thank you very much for any
reply.
Yours sincerely,
Chaofu Wu