Wait! wait! Axel, can I answer this one?
pair_style hybrid airebo 3.0 1 0 lj/cut 2.5
pair_coeff * * airebo CH.airebo C H NULL
#pair_style hybrid tersoff lj/cut 2.5
#pair_coeff * * tersoff Si.tersoff Si Si NULL
pair_coeff 2 3 lj/cut 1.0 1.0 2.5
pair_coeff 1 3 lj/cut 1.0 1.0 2.5
pair_coeff 3 3 lj/cut 1.0 1.0 2.5
Please note the subtle difference, look for it, you’ll find it. And yes you can leave the additional arguments in.
dave