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talbers Offline OP
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Hello!

I would like to derive parameters for 1-Phenylpyrazole, in particular, I'd like to optimize the charges that fall out of the Paramchem website.

But there are serious convergence problems with the probe water for N(1) during QM geometry optimization - I restrained the H-N(1)-N(2) and H-N(1)-C(5) angles to be 90 degrees. Is this appropiate at all? Where should the probe water go for atoms in aromatic rings that bear a hydrogen or other substituent, and what are the recommendations to improve convergence?

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rmv Online Content
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Have you gone through the CGenFF tutorials yet?


Rick Venable
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talbers Offline OP
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See, that's the question. When you have CH groups or heteroatoms in your heteroaromatic compound you put the probe water into the equatorial plane and adjust charges accordingly.

But what to do when the equatorial position is occupied by a substituent (like in 1-phenylpyrazole), or when you have, say, a trifluoromethyl group that interferes with adjacent equatorial positions? I haven't found that case in the tutorial.

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It doesn't look like the N atoms of 1-Phenylpyrazole should have any bonded H atoms at all.

I believe the general idea is to put water molecules in places where they are strongly interacting with the fragment under study, in order to investigate the impact on the partial charges.


Rick Venable
computational chemist


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