Question about "pair_style hbond/dreiding/lj command"

Hi LAMMPS users,
I want to use pair_style hbond/dreiding/lj command in my force field.
I can’t understand one thing: in the original DREIDING potential of (Mayo & Co.) there are no references about the parameters inner_distance_cutoff, outer_distance_cut_off.
what do they mean?

Best regards

Nicola

I think LAMMPS requires you to specify some kind of distance cut off
between all particles (for non-bonded interactions at least), even if
you don't want to use one.

The inner and outer distance cutoffs are parameters for the S(r)
function which truncates the force between the (donor & acceptor)
atoms. Their are two cutoffs. (When "r" lies between between the
inner and outer distance cutoffs, the attractive or repulsive force
between atoms is increased so that the energy between atoms at shorter
distances remains unaffected.)
  The S(r) function is also used in the lj/charm pair styles. The
formula for that function is here:
http://lammps.sandia.gov/doc/pair_hbond_dreiding.html
http://lammps.sandia.gov/doc/pair_charmm.html

It's true that the Mayo et. al 1990 study does not use distance
cutoffs. There was a footnote on the bottom-left on page 7 of that
paper mentioning that cutoffs are convenient, and their example
suggests that "9.0" Angstroms would be a typical cutoff distance.

I'm not sure if I answered your question.
Cheers

Andrew