--- trunk/OOPSE/libmdtools/calc_reaction_field.F90	2003/04/09 04:06:43	483
+++ trunk/OOPSE/libmdtools/calc_reaction_field.F90	2003/07/15 17:10:50	611
@@ -237,15 +237,21 @@ contains
        
        if (do_stress) then          
           if (molMembershipList(atom1) .ne. molMembershipList(atom2)) then
-             tau_Temp(1) = tau_Temp(1) + dudx * d(1)
-             tau_Temp(2) = tau_Temp(2) + dudx * d(2)
-             tau_Temp(3) = tau_Temp(3) + dudx * d(3)
-             tau_Temp(4) = tau_Temp(4) + dudy * d(1)
-             tau_Temp(5) = tau_Temp(5) + dudy * d(2)
-             tau_Temp(6) = tau_Temp(6) + dudy * d(3)
-             tau_Temp(7) = tau_Temp(7) + dudz * d(1)
-             tau_Temp(8) = tau_Temp(8) + dudz * d(2)
-             tau_Temp(9) = tau_Temp(9) + dudz * d(3)
+
+             ! because the d vector is the rj - ri vector, and 
+             ! because dudx, dudy, and dudz are the
+             ! (positive) force on atom i (negative on atom j) we need
+             ! a negative sign here:
+
+             tau_Temp(1) = tau_Temp(1) - d(1) * dudx
+             tau_Temp(2) = tau_Temp(2) - d(1) * dudy
+             tau_Temp(3) = tau_Temp(3) - d(1) * dudz
+             tau_Temp(4) = tau_Temp(4) - d(2) * dudx
+             tau_Temp(5) = tau_Temp(5) - d(2) * dudy
+             tau_Temp(6) = tau_Temp(6) - d(2) * dudz
+             tau_Temp(7) = tau_Temp(7) - d(3) * dudx
+             tau_Temp(8) = tau_Temp(8) - d(3) * dudy
+             tau_Temp(9) = tau_Temp(9) - d(3) * dudz
              virial_Temp = virial_Temp + &
                   (tau_Temp(1) + tau_Temp(5) + tau_Temp(9))
           endif