[gmx-users] Problem with free energy calculation

Oliver Konrad Oliver.Konrad at job-stiftung.de
Wed Jun 26 15:38:42 CEST 2002

David van der Spoel wrote:

> On Tue, 2002-06-25 at 16:15, Oliver Konrad wrote:
>>Hi all,
>>i´m trying an free energy calculation of the solvation energy for one
>>methane molecule in a box of water.
>>I have made 20 simulations for different values of lambda from 0 to 1
>>and integrated the resulting free energy, but the energy is far too
>>large. I got a solvation energy of nearly 30 kJ/mol.!!
> Did you make appropriate cut-ff corrections etc.? Is this a mutation
>>from water to methanol?

I left the Water-molecules untouched and mutate the OPLS Methane to an 
Dummy-Particle with the same mass as Methane but without interactions to 
  the water (TIP4P) molecules.
I have taken the average value of free energy for each lambda over the 
last 150 ps of the simulation and integrated with xmgrace. Because the 
result (30kJ/mol) for the solvation of methane in water is so much 
greater than the experimental value of 8.4 kJ/mol i have done no 
long-range corrections.

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