add attr

Author: ChiahsinChu

dmff/generators/qeq.py

@@ -131,6 +131,7 @@ def createPotential(
             r_cut = nonbondedCutoff.value_in_unit(unit.nanometer)
         else:
             r_cut = nonbondedCutoff
+        self.r_cut = r_cut
 
         if not isNoCut:
             cell = topdata.getPeriodicBoxVectors()
@@ -171,6 +172,7 @@ def createPotential(
                 aidx = [a.index for a in r.atoms()]
                 const_list.append(aidx)
                 const_vals.append(sum(init_q[aidx]))
+        self.n_const = len(const_vals)
 
         has_aux = False
         if "has_aux" in kwargs: