fix

user-doc/tutorials/aa-lugano-6b.txt

@@ -137,14 +137,14 @@ Below you can find reference results
 \subsection lugano-6b-ex-4 Exercise 4: Standard affinity
 
 Now use the weights that you computed in the previous exercise to
-compute the standard affinity of the Mg to the phosphate. In order to do
+compute the absolute binding affinity of the Mg to the phosphate. In order to do
 so you should compute the relative probability of seeing the Mg bound to the phosphate
-and in the bulk region.
+and in the bulk region and normalize to 1 mol/M concentration.
 
-For instance, if you define bulk the region between 1.5 and 2.5 angstrom, you should multiply the 
+For instance, if you define bulk the region between 1.5 and 2.5 angstrom, you should divide the 
 weight of the unbound state by a factor \f$ \frac{4\pi}{3}(2.5^3-1.5^3)/V_{mol} \f$
 where \f$V_{mol}=1.66\f$ is the volume corresponding to the inverse of 1 mol/L concentration.
-
+The absolute binding affinity is then defined as \f$-k_BT \log \frac{w_B}{w_U} \f$.
 You should obtain a value of approximately 50.4 kj/mol
 
 \warning The trajectory is too short (approx 20ns) to obtain converged results!