git-svn-id: svn://svn.icms.temple.edu/lammps-ro/trunk@14876 f3b2605a-c512-4ea7-a41b-209d697bcdaa

src/fix_momentum.cpp

@@ -64,10 +64,13 @@ FixMomentum::FixMomentum(LAMMPS *lmp, int narg, char **arg) :
         zflag < 0 || zflag > 1)
       error->all(FLERR,"Illegal fix momentum command");
 
-  // cannot have 0 atoms in group
-
-  if (group->count(igroup) == 0)
-    error->all(FLERR,"Fix momentum group has no atoms");
+  dynamic_group_allow = 1;
+  if (group->dynamic[igroup]) {
+    dynamic = 1;
+  } else {
+   if (group->count(igroup) == 0)
+     error->all(FLERR,"Fix momentum group has no atoms");
+  }
 }
 
 /* ---------------------------------------------------------------------- */
@@ -96,6 +99,13 @@ void FixMomentum::end_of_step()
   double ekin_old,ekin_new;
   ekin_old = ekin_new = 0.0;
 
+  if (dynamic)
+    masstotal = group->mass(igroup);
+
+  // do nothing is group is empty, i.e. mass is zero;
+
+  if (masstotal == 0.0) return;
+
   // compute kinetic energy before momentum removal, if needed
 
   if (rescale) {

src/fix_momentum.h

@@ -34,6 +34,7 @@ class FixMomentum : public Fix {
  private:
   int linear,angular,rescale;
   int xflag,yflag,zflag;
+  int dynamic;
   double masstotal;
 };
 

src/kspace.cpp

@@ -307,6 +307,15 @@ double KSpace::estimate_table_accuracy(double q2_over_sqrt, double spr)
 {
   double table_accuracy = 0.0;
   int nctb = force->pair->ncoultablebits;
+  if (comm->me == 0) {
+    char str[128];
+    if (nctb)
+      sprintf(str,"Using %d-bit tables for long-range coulomb",nctb);
+    else
+      sprintf(str,"Using polynomial approximation for long-range coulomb");
+    error->warning(FLERR,str);
+  }
+
   if (nctb) {
     double empirical_precision[17];
     empirical_precision[6] =  6.99E-03;