[gmx-users] 'hydration energy'

[Markus O Kaukonen]

Dear All,

Sometime ago I asked about my strange results when looking at
hydaration energy of some positively charged ions.

I managed to reproduce the strange results and compare them to
results of ion charging free energies by Darden et al
(J.Chem.Phys v109, pp10921-10935, y1998).

The reason for strange results was that I had used unconstrained
ffopls water molecules with conjugate gradient minimisation.
In big water cells this leads to increasing error.

If I use constrained water and steepest descent the results are
compareable to literature data.

However, in my opinion conjugate gradient is much more efficient compared
to steepest descent (in contrary what gromacs manual is saying).
I guess it can more easily overcome small energy barriers.

Maybe I'll use l-bfgs in the future, though have not yet experinece on it.

Terveisin Markus

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