[gmx-users] Solvation Free energy Calculation

[Paolo Cerri]

Dear all,

I'm trying to calculate solvation free energy for an ALANINE molecule in
water with the usual method: I calculate dG/dlambda for different values
of lambda and then integrate.
I start with my molecule fully interacting with solvent (water SPC) and
then decouple the solute-solvent Coulombic interaction while leaving LJ
parameters unchanged. As much as I know this part should not give
problems since the singularities shows up when decoupling Lennard-Jones.
My curve is actually spike free but dG/dlambda shows deviations up to 10
kjoule/mol). 

As for the LJ decoupling,I cannot obtain a smooth curve and dG/dlambda
has large deviations even if I use sc_alpha = 0.5 and sc_power = 1 as
suggested by Shirts.

I use OPLS-AA forcefield

I think that there is probably something that I am missing but i don't
know what. 

Paolo