Is it possible to measure infinite dilution activity coefficient of pharmaceutical solutes in water via molecular dynamics using conventional force fields with acceptable accuracy? 

Activity coefficient defined as ratio of Henry's constant of the solute in water to its (solute) chemical potential  at pure state. So it involves two free energy calculations, free energy of transfer of drug to water and corresponding value for transfer of drug to its pure hypothetical liquid state.

I am wondering about the feasibility of the later case.