--- branches/development/src/nonbonded/LJ.cpp	2011/07/08 20:25:32	1587
+++ branches/development/src/nonbonded/LJ.cpp	2011/11/22 20:38:56	1665
@@ -36,7 +36,8 @@
  * [1]  Meineke, et al., J. Comp. Chem. 26, 252-271 (2005).             
  * [2]  Fennell & Gezelter, J. Chem. Phys. 124, 234104 (2006).          
  * [3]  Sun, Lin & Gezelter, J. Chem. Phys. 128, 24107 (2008).          
- * [4]  Vardeman & Gezelter, in progress (2009).                        
+ * [4]  Kuang & Gezelter,  J. Chem. Phys. 133, 164101 (2010).
+ * [5]  Vardeman, Stocker & Gezelter, J. Chem. Theory Comput. 7, 834 (2011).
  */
 
 #include <stdio.h>
@@ -284,7 +285,7 @@ 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;
   }