Which of the QM/MM models is the best? This is a difficult question to answer because there are many different measures of quality. For example, one measure would be to compare the location of water molecules in the first solvation shell around each side-chain against what is known from experiment. Perhaps the best measure for this calculation is to compare each of the QM/MM relative hydration free energies against the experimental value.

Exercise 7: Comparing the QM/MM and MM free energies against experiment

The experimental relative hydration free energy of PHE and TRP is -5.1 kcal mol-1.

QUESTION 7.1 - How does the experimental relative hydration free energy compare to that calculated using MM and QM/MM?

QUESTION 7.2 - Which is the best method? Why do you think that this is the case?

If you get stuck or need help, you can take a peek at this model answer for exercise 7.

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