Simplifying behavior of bpm bonds without breakage

doc/src/bond_bpm_rotational.rst

@@ -154,8 +154,10 @@ page on BPMs.
 
 If the *break* keyword is set to *no*, LAMMPS assumes bonds should not break
 during a simulation run. This will prevent some unnecessary calculation.
-However, if a bond reaches a damage criterion greater than one,
-it will trigger an error.
+The recommended bond communication distance no longer depends on bond failure
+coefficients (which are ignored) but instead corresponds to the typical heurestic
+maximum strain used by typical non-bpm bond styles. One cannot use *break no*
+with *smooth yes*.
 
 If the *store/local* keyword is used, an internal fix will track bonds that
 break during the simulation. Whenever a bond breaks, data is processed

doc/src/bond_bpm_spring.rst

@@ -117,8 +117,10 @@ page on BPMs.
 
 If the *break* keyword is set to *no*, LAMMPS assumes bonds should not break
 during a simulation run. This will prevent some unnecessary calculation.
-However, if a bond reaches a strain greater than :math:`\epsilon_c`,
-it will trigger an error.
+The recommended bond communication distance no longer depends on the value of
+:math:`\epsilon_c` (which is ignored) but instead corresponds to the typical
+heurestic maximum strain used by typical non-bpm bond styles. One cannot use
+*break no* with *smooth yes*.
 
 .. versionadded:: TBD
 

src/BPM/bond_bpm.cpp

@@ -331,6 +331,9 @@ void BondBPM::settings(int narg, char **arg)
 
 double BondBPM::equilibrium_distance(int /*i*/)
 {
+  if (!break_flag)
+    return r0_max_estimate;
+
   // Ghost atoms may not yet be communicated, this may only be an estimate
   if (r0_max_estimate == 0) {
     if (!fix_bond_history->restart_reset) {

src/BPM/bond_bpm_rotational.cpp

@@ -523,7 +523,7 @@ void BondBPMRotational::compute(int eflag, int vflag)
     breaking = elastic_forces(i1, i2, type, r_mag, r0_mag, r_mag_inv, rhat, r, r0, force1on2,
                               torque1on2, torque2on1);
 
-    if (breaking >= 1.0) {
+    if ((breaking >= 1.0) && break_flag) {
       bondlist[n][2] = 0;
       process_broken(i1, i2);
       continue;
@@ -684,6 +684,9 @@ void BondBPMRotational::settings(int narg, char **arg)
       error->all(FLERR, "Illegal bond bpm command, invalid argument {}", arg[iarg]);
     }
   }
+
+  if (smooth_flag && !break_flag)
+    error->all(FLERR, "Illegal bond bpm command, must turn off smoothing with break no option");
 }
 
 /* ----------------------------------------------------------------------

src/BPM/bond_bpm_spring.cpp

@@ -245,7 +245,7 @@ void BondBPMSpring::compute(int eflag, int vflag)
     r = sqrt(rsq);
     e = (r - r0) / r0;
 
-    if (fabs(e) > ecrit[type]) {
+    if ((fabs(e) > ecrit[type]) && break_flag) {
       bondlist[n][2] = 0;
       process_broken(i1, i2);
 
@@ -485,6 +485,9 @@ void BondBPMSpring::settings(int narg, char **arg)
       error->all(FLERR, "Illegal bond bpm command, invalid argument {}", arg[iarg]);
     }
   }
+
+  if (smooth_flag && !break_flag)
+    error->all(FLERR, "Illegal bond bpm command, must turn off smoothing with break no option");
 }
 
 /* ----------------------------------------------------------------------