CHARMM Development Project Forums User Discussion & Questions Parameter Set Discussion Parameters for hydronium ion?

Dear Users

I would like to know if the hydronium ion has been ever parametrized. If not, how appropriate is to transfer parameters from the TIP3 residue?

thanks

I haven't heard of any hydronium parameters. My suggestion
would be to determine intearction energies and geometries
between hydronium and water at the HF/6-31G* level.
Then convert TIP3P to hydronium and then adjust
the hydronium charges to reproduce the QM interaction
energies. Note that you will have to adjust the bond lengths
and I would treat the hydronium as rigid via shake.
The final test will be calculation of the free energy
of solvation.

Note that info on the parameter development approachs
are on my web page.

alex

of solvation of the

Thanks for the reply, alex.
My work requires including this hydronium ion in the QM region of the QM/MM calculation with CHARMM and MOPAC. I need to give parameters to the hydronium ion in order to save a top and crd files to start charmm exe, though this water will eventually be QM, so I don't need the classical parameters. Is it ok to approximate the hydronium ion parameters to the water, just because it will eventually be just QM?

thanks