--- trunk/src/nonbonded/Electrostatic.cpp	2013/08/23 15:59:23	1933
+++ trunk/src/nonbonded/Electrostatic.cpp	2013/10/31 15:32:17	1938
@@ -40,6 +40,10 @@
  * [5]  Vardeman, Stocker & Gezelter, J. Chem. Theory Comput. 7, 834 (2011).
  */
 
+#ifdef IS_MPI
+#include <mpi.h>
+#endif
+
 #include <stdio.h>
 #include <string.h>
 
@@ -57,9 +61,6 @@
 #include "math/erfc.hpp"
 #include "math/SquareMatrix.hpp"
 #include "primitives/Molecule.hpp"
-#ifdef IS_MPI
-#include <mpi.h>
-#endif
 
 namespace OpenMD {
   
@@ -1440,7 +1441,7 @@ namespace OpenMD {
                   Q = atom->getQuadrupole() * mPoleConverter; 
                   Qk = Q * kVec;                  
                   qk = dot(kVec, Qk);
-                  qxk[i] = cross(kVec, Qk);
+                  qxk[i] = -cross(kVec, Qk);
                   qkc[i] = qk * ckr[i];
                   qks[i] = qk * skr[i];
                 }