Firefly and PC GAMESS-related discussion club

 
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Tatiana Alieva
vishnevoe00@list.ru

According to the authors: "In popular quantum chemistry packages such as Gaussian03 and GAMESSPLUS, the term (Esoln + Gnes) is misleadingly referred to as the total free energy in solution, including nonelectrostatic contributions .... As a result, this term has mistakenly been used as the solution-phase free energy in the literature. To extract the solution-phase free energy from a continuum model calculation it is instead necessary to perform the gas-phase thermal corrections and use eq 4."

Eq.4: Gsoln = Esoln + Gnes + ΔGcorr_gas

where Esoln ... refer to the electronic energy of the solute in the presence of the continuum solvent field, and Gnes denotes the sum of any nonelectrostatic contributions (e.g., cavitation and dispersion-repulsion interactions) to the solvation free energy.
ΔGcorr_gas refers to the thermal correction to the free energy of the solute in the gas phase, not the solution phase.

The authors agree, that eg. 4 looks "rather counterintuitively", however it is correct since "any noncanceling differences in the thermal contributions in the two phases (e.g., entropic changes associated with structural reorganization of the solvent) are indirectly incorporated into (Esoln + Gnes) through parametrization of eq 3 to reproduce experimental solvation free energie".

Is it the case for Firefly too? So that to get the solution-phase free energy the thermal correction to the free energy of the solute in the gas has to be added to Firefly's TOTAL FREE ENERGY IN SOLVENT?

P.S. I'd recommend to read the above-mentioned article at least to beginners in PCM.



On Thu Mar 13 '14 3:58pm, Tatiana Alieva wrote
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>Hallo to all once more,

>The question in the title was vague for me all the time. I've failed to find a clear answer in the firefly documentation.
>1) Does TOTAL FREE ENERGY IN SOLVENT include entropy contribution of a solute?

>And
>2) Why in e.g. MP2 energy calculation  FREE ENERGY IN SOLVENT =  E(0), not =E(MP2) from RHF-MP2 ENERGY CALCULATION?

>Perhaps, It would be a good thing if the contributions to the TOTAL FREE ENERGY IN SOLVENT were explicitly documented in the Firefly manual... If this term really doesn't include the entropy contribution from the solute, then better write down this explicitly.

>I will be grateful for your answer.
>Tatiana