[gmx-users] Some questions about free energy calculation

[nicolis at guideo.fr]

Hello,
I want to compute the solvation energy for some metal cations. After 
reading the manual I understand that it is possible to do such a 
calculation with gromacs using a lamda parameter to generate smoothly 
a metal in a box of water. Is my interpretation correct? Is this the right way 
to proceed?
If yes, I see that I have to define free_energy=yes in the .mdp file but with 
which integrator?
And another question: I see that the lamda is used to shift from topology A 
to B, but where do I feed the two topologies? In grompp ot in mdrun?
I looked all the manual pages that seemed relevant but I was not able to 
find the info. If you can point me to the correct place to look, thank you

Yiannis