particel insertion method



 Hi:
         I am doing a simple  calculation on the solvation energy of lipid head
 groups in the
 membrane--protein system,   and would be interested if some one could tell me
 where to find some
 basic references for the particle insertion method for free energy calculation.
 The method that I
 am using for the free energy (mostly due to electrostatic interactions ) is the
 following:    perform a
 simulation  1  for the system with charge set A,   and perform another
 simulation 2 with charge set
 B.   Then,  calculate the energy difference of changing the charges from  A to B
 using trajectories
 from simulation 1  to obtain  e1 (A->B),   and similarly calculate the energy
 difference using
 trajectory 2  e2(A->B).   Finally,  calculate the free energy from the
 average of these two.    I
 wonder whether anybody has used this kind of method before and whether this is a
 reasonably
 accurate method to use for solvation energy calculations.
           I will collect the information I get and post a summary.   Thanks.
 Feng