--- trunk/OOPSE/libmdtools/calc_LJ_FF.F90	2003/04/11 18:46:37	491
+++ trunk/OOPSE/libmdtools/calc_LJ_FF.F90	2003/07/15 17:10:50	611
@@ -2,7 +2,7 @@
 !! Corresponds to the force field defined in lj_FF.cpp 
 !! @author Charles F. Vardeman II
 !! @author Matthew Meineke
-!! @version $Id: calc_LJ_FF.F90,v 1.6 2003-04-11 18:46:37 mmeineke Exp $, $Date: 2003-04-11 18:46:37 $, $Name: not supported by cvs2svn $, $Revision: 1.6 $
+!! @version $Id: calc_LJ_FF.F90,v 1.7 2003-07-15 17:10:50 gezelter Exp $, $Date: 2003-07-15 17:10:50 $, $Name: not supported by cvs2svn $, $Revision: 1.7 $
 
 module lj
   use definitions
@@ -265,16 +265,21 @@ contains
 #endif
 
           if (molMembershipList(id1) .ne. molMembershipList(id2)) then
+ 
+             ! because the d vector is the rj - ri vector, and 
+             ! because fx, fy, fz are the force on atom i, we need a
+             ! negative sign here:
 
-             tau_Temp(1) = tau_Temp(1) + fx * d(1)
-             tau_Temp(2) = tau_Temp(2) + fx * d(2)
-             tau_Temp(3) = tau_Temp(3) + fx * d(3)
-             tau_Temp(4) = tau_Temp(4) + fy * d(1)
-             tau_Temp(5) = tau_Temp(5) + fy * d(2)
-             tau_Temp(6) = tau_Temp(6) + fy * d(3)
-             tau_Temp(7) = tau_Temp(7) + fz * d(1)
-             tau_Temp(8) = tau_Temp(8) + fz * d(2)
-             tau_Temp(9) = tau_Temp(9) + fz * d(3)
+             tau_Temp(1) = tau_Temp(1) - d(1) * fx
+             tau_Temp(2) = tau_Temp(2) - d(1) * fy
+             tau_Temp(3) = tau_Temp(3) - d(1) * fz
+             tau_Temp(4) = tau_Temp(4) - d(2) * fx
+             tau_Temp(5) = tau_Temp(5) - d(2) * fy
+             tau_Temp(6) = tau_Temp(6) - d(2) * fz
+             tau_Temp(7) = tau_Temp(7) - d(3) * fx
+             tau_Temp(8) = tau_Temp(8) - d(3) * fy
+             tau_Temp(9) = tau_Temp(9) - d(3) * fz
+             
              virial_Temp = virial_Temp + &
                   (tau_Temp(1) + tau_Temp(5) + tau_Temp(9))