improper dihedrals

Hello,

I am in the process of defining a LAMMPS data file for 1,3-dimethylimidazolium (dmim). The force field which I am using (CLaP force field - Canongia Lopes et al.) requires 2 improper dihedrals from the AMBER force field.

I have defined the coefficients as follows in my data file according to the cvff improper_style :