Ensemble generation for charged complexes qcg

[froze-jameel]

Hello, i have been trying to generate ensemble using a charged molecule as solute and acetonitrile as solvent using crest QCG. However in the resulted QCG structures i see that the solvent interacts with the solute thus, protonating the solute. What i would like to ask that, if there exist a way where to generate an solute solvent ensemble for charged complexes with the solvent protonating or de-protonating the solute species. Thanks

[cplett]

Hi, currently, there is possibility to define protonation states in QCG. But if you want a certain protonation state that is not favored by our GFN methods, you might add your solute with one added solvent molecule in the protonation state you desire as input for the solute and constrain this geometry by using, for example, the "--fixsolute" to keep your protonation state.

[froze-jameel]

Thanks for the reply, my question is the other way around, i do not want my molecule to be protonated by the solvent molecules. In the test calculation the solvent such as acetonitrile, water, methanol and acetic acid all are protonating the solute. I use "--fixsolute" for my calculation. Where solute is the charged molecule.

[haneug]

For what purpose do you want to generate this ensemble? Can you say if this is just a GFN artifact? Does the same protonation occur in a DFT optimization with a single solvent molecule nearby? Maybe your solute simply is protonated in solution? If you want to generate your artificial clusters nevertheless you could try to generate the clusters for the protonated solute. Then move the proton back to the solvent and optimize the cluster with a forcefield e.g. GFN-FF. A forcefield can not generate new bonds and therefore protonation should not occur. best Hagen

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