add check to disallow custom neighbor list cutoffs larger than the communication cutoff.

src/neighbor.cpp

@@ -837,9 +837,20 @@ int Neighbor::init_pair()
   //     similar to what vanilla Nbin::coord2atom() does now in atom2bin
 
   if (style == Neighbor::BIN) {
-    for (i = 0; i < nrequest; i++)
+    for (i = 0; i < nrequest; ++i)
       if (requests[i]->occasional && requests[i]->ghost)
-        error->all(FLERR,"Cannot request an occasional binned neighbor list with ghost info");
+        error->all(FLERR, "Cannot request an occasional binned neighbor list with ghost info");
+  }
+
+  // check requests with a custom neighbor list cutoff to make sure the cutoff is within
+  // the communication cutoff.  For perpetual lists, neighbor list skin is added later.
+
+  const double comm_cutoff = comm->get_comm_cutoff();
+  for (i = 0; i < nrequest; ++i) {
+    if (requests[i]->cut) {
+      if (comm_cutoff < (requests[i]->cutoff + (requests[i]->occasional ? 0.0 : skin)))
+        error->all(FLERR, "Custom neighbor list cutoff too large for communication cutoff");
+    }
   }
 
   // morph requests in various ways