--- trunk/OOPSE/libmdtools/Molecule.cpp	2004/04/27 16:26:44	1136
+++ trunk/OOPSE/libmdtools/Molecule.cpp	2004/04/28 22:34:02	1140
@@ -12,7 +12,7 @@ Molecule::Molecule( void ){
   myBonds = NULL;
   myBends = NULL;
   myTorsions = NULL;
-
+  hasMassRatio = false;
 }
 
 Molecule::~Molecule( void ){
@@ -42,8 +42,7 @@ void Molecule::initialize( molInit &theInit ){
 
 
 void Molecule::initialize( molInit &theInit ){
-  double totMass;
-  
+
   nAtoms = theInit.nAtoms;
   nMembers = nAtoms;
   nBonds = theInit.nBonds;
@@ -63,12 +62,6 @@ void Molecule::initialize( molInit &theInit ){
   for (int i = 0; i < myRigidBodies.size(); i++) 
       myRigidBodies[i]->calcRefCoords();
 
-
-  //the mass ratio will never change during the simulation. Thus, we could
-  //just calculate it at the begining of the simulation
-  totMass = getTotalMass();
-  for(int i = 0; i < nAtoms; i ++)
-    myAtoms[i]->setMassRatio(myAtoms[i]->getMass()/totMass);  
 }
 
 void Molecule::calcForces( void ){
@@ -80,6 +73,15 @@ void Molecule::calcForces( void ){
     myRigidBodies[i]->updateAtoms();
   }
 
+  //the mass ratio will never change during the simulation. Thus, we could
+  //just calculate it at the begining of the simulation
+  if (!hasMassRatio){
+    double totMass = getTotalMass();
+    for(int i = 0; i < nAtoms; i ++)
+      myAtoms[i]->setMassRatio(myAtoms[i]->getMass()/totMass);  
+    hasMassRatio =  true;
+  }
+
   //calculate the center of mass of the molecule
   getCOM(com);  
   for(int i = 0; i < nAtoms; i ++)