[gmx-users] the problem about the calculation free energy of the toluene in water

[Jinyao Wang]

hi,gmx-users

	 I am  repeating the calculation of the toluene in water using GMX 4.0.4.
I have read the maillist about the the solvation free energy of toluene in water. 
I know that the sc-power and the point lambda are very important. So I set sc-power=2 and 25 lambda points.
Now I get the free energy in vacuo is -2.85 Kj/mol, but I get the free energy in water is -2.12 Kj/mol. So the deltaG_hyd= -2.85 + 2.12 = -0.73 Kj/mol instead of -3.1 Kj/mol in manual. I don't know how to improve the free energy value in water.

This is my md-lambda088.mdp

cpp                 =  /lib/cpp
constraints         =  all-bonds
integrator          =  md
tinit               =  0.0
dt                  =  0.002    
nsteps              =  50000      
nstcomm             =  1
nstxout             =  25000
nstvout             =  0
nstfout             =  0
nstlog              =  100
nstenergy           =  100
nstxtcout           =  1000
xtc_precision       =  1000
xtc_grps            =  Protein
nstlist             =  5
energygrps          =  Protein SOL
ns_type             =  grid
rlist               =  0.9
coulombtype         =  Reaction-Field
epsilon_r           =  78.0
rcoulomb            =  1.4
rvdw                =  1.4
Tcoupl              =  Berendsen
tc-grps             =  Protein SOL
ref_t               =  300 300
tau_t               =  0.1 0.1
Pcoupl              =  Berendsen
tau_p               =  1.0
compressibility     =  4.6e-5
ref_p               =  1.0
free_energy         =  yes
init_lambda         =  0.88
sc-alpha            =  1.51
sc-power            =  2.0  


 				



　　　　　　　　Jinyao Wang
　　　　　　　　wangjy at ciac.jl.cn
　　　　　　　　　　2009-09-15