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Re^2: solvent effect

sanya
sanya@photonics.ru


HF is strongly aggregated; even in the gas phase it exists as H2F2. So, it is not a good benchmark molecule.

Anyway, in case of hydrogen-bonding systems (that is, most water-soluble compounds), the first solvation shell (at least, the solvent molecules immediatly H-bonded to the solute) should be considered explicitly as QM molecules or as effective fragment potentials.

On Thu Feb 13 '14 11:21am, Thomas Pijper wrote
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>Dear David,

>Are you sure that HF is a good 'benchmark' to investigate solvation effects? HF is a strong acid and will almost fully dissociate into H+ and F- in water. I would also expect some dissociation when in benzene. As such, your current model of dissolved HF is not very realistic.
>
>
>Kind regards,
>Thom
>
>
>On Thu Feb 13 '14 6:33am, David G. wrote
>----------------------------------------
>>Hi

>>As a test to understand how Firefly does compute and consider solvent effects the free energy of HF diatomic molecule has been calculated in gaseous state, water, and benzene to compare the results.

>>free energy of HF (gaseous) : -100.426656 - 18.394/2625.5 = -100.433662 H
>>free energy of HF (water): -100.433893 H
>>free energy of HF (benzene): -100.430009 H

>>we expected a larger difference between the values in water and benzene since HF is a highly polar molecule. I have attached the input/output files and I appreciate any comment to help us how to improve the results if it looks unwise in this state. Many Thanks
>>
>>
>>Sincerely, David
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[ This message was edited on Sun Feb 16 '14 at 2:01am by the author ]


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