--- branches/development/src/nonbonded/LJ.cpp	2010/10/03 22:18:59	1505
+++ branches/development/src/nonbonded/LJ.cpp	2011/04/27 18:38:15	1549
@@ -240,13 +240,12 @@ namespace OpenMD {
     }    
   }
  
-  void LJ::calcForce(InteractionData idat) {
+  void LJ::calcForce(InteractionData &idat) {
     
     if (!initialized_) initialize();
     
-    pair<AtomType*, AtomType*> key = make_pair(idat.atype1, idat.atype2);
     map<pair<AtomType*, AtomType*>, LJInteractionData>::iterator it;
-    it = MixingMap.find(key);
+    it = MixingMap.find(idat.atypes);
     
     if (it != MixingMap.end())  {
       
@@ -285,9 +284,8 @@ namespace OpenMD {
       RealType dudr = idat.sw * idat.vdwMult * epsilon * (myDeriv - 
                                                           myDerivC)*sigmai;
       
-      idat.pot += idat.sw * pot_temp;
-      idat.f1 = idat.d * dudr / idat.rij;
-      
+      idat.pot[0] += idat.sw * pot_temp;
+      idat.f1 = idat.d * dudr / idat.rij;      
     }
     return;
   }
@@ -307,11 +305,10 @@ namespace OpenMD {
     return;
   }
   
-  RealType LJ::getSuggestedCutoffRadius(AtomType* at1, AtomType* at2) {
+  RealType LJ::getSuggestedCutoffRadius(pair<AtomType*, AtomType*> atypes) {
     if (!initialized_) initialize();   
-    pair<AtomType*, AtomType*> key = make_pair(at1, at2); 
     map<pair<AtomType*, AtomType*>, LJInteractionData>::iterator it;
-    it = MixingMap.find(key);
+    it = MixingMap.find(atypes);
     if (it == MixingMap.end()) 
       return 0.0;
     else  {