--- branches/development/src/nonbonded/LJ.cpp	2011/06/16 22:00:08	1583
+++ branches/development/src/nonbonded/LJ.cpp	2011/09/14 21:15:17	1629
@@ -242,7 +242,7 @@ namespace OpenMD {
   void LJ::calcForce(InteractionData &idat) {
     
     if (!initialized_) initialize();
-    
+
     map<pair<AtomType*, AtomType*>, LJInteractionData>::iterator it;
     it = MixingMap.find( idat.atypes );
     
@@ -284,7 +284,7 @@ namespace OpenMD {
                                                                 myDerivC)*sigmai;      
 
       (*(idat.pot))[VANDERWAALS_FAMILY] += *(idat.sw) * pot_temp;
-      *(idat.f1) = *(idat.d) * dudr / *(idat.rij);
+      *(idat.f1) += *(idat.d) * dudr / *(idat.rij);
     }
     return;
   }