CCL: question on free energy/constant of dissociation estimation for protein-ligand complex (X-ray)

 Sent to CCL by: Andrew Voronkov [drugdesign :]
 Dear CCL users, there is plethora of methods for estimation of the free energy
 of protein-ligand binding. Which software among the fastest is most accurate in
 evaluation of the free energy of binding for a given protein-ligand complex
 (X-ray). I need to thoeretically calculate constant of protein-ligand complex
 Best regards,