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Alex Granovsky
gran@classic.chem.msu.su

I'm sorry for the delay with my reply.

>Thank you for your reply. In addition to the message that you clarify it Please let us know why the following terms are called free energy ? the lines were copied from a PCM calculation.

These terms are called free energy because they include the work
to be done to self-consistently polarize an environment
(i.e. solvent molecules), not just the internal energy of solute.

>In fact in PCM calculation no vibrational analysis is done so I wonder why the term should be called free energy and what are the H(0) and V/2 operators ?

H(0) is the Hamiltonian in the absence of solvent,
V is the perturbation due to solute-solvent interaction.
V/2 arises as a part describing the increase of the internal
energy and the same amount of energy is the work to be done
to polarize solvent.

Hope this helps,
Alex


On Thu Feb 20 '14 10:05pm, David G. wrote
-----------------------------------------
>>Dear Alex

>Thank you for your reply. In addition to the message that you clarify it Please let us know why the following terms are called free energy ? the lines were copied from a PCM calculation.

>            ----------------------------------------------
>             ------   RESULTS OF D-PCM CALCULATION  -------
>             ----------------------------------------------

> FREE ENERGY IN SOLVENT =       =     -100.4300085340 A.U.
> INTERNAL ENERGY IN SOLVENT =       =     -100.4265000845 A.U.
> DELTA INTERNAL ENERGY =         =        0.0000000000 A.U.
> ELECTROSTATIC INTERACTION = 1/2(PB+PC) + 1/2PX + UNZ=       -0.0035084495 A.U.
> PIEROTTI CAVITATION ENERGY                          =        0.0000000000 A.U.
> DISPERSION FREE ENERGY                              =        0.0000000000 A.U.
> REPULSION FREE ENERGY                               =        0.0000000000 A.U.
> TOTAL INTERACTION (DELTA + ES + CAV + DISP + REP)   =       -0.0035084495 A.U.
> TOTAL FREE ENERGY IN SOLVENT                        =     -100.4300085340 A.U.
>     PB  =    17.22941062 A.U.   PC  =    17.23293229 A.U.
>     PX  =   -17.27908407 A.U.   UNZ =    -8.59513787 A.U.

> FREE ENERGY IN SOLVENT       =      -63020.79 KCAL/MOL
> INTERNAL ENERGY IN SOLVENT   =      -63018.59 KCAL/MOL
> DELTA INTERNAL ENERGY        =           0.00 KCAL/MOL
> ELECTROSTATIC INTERACTION    =          -2.20 KCAL/MOL
> PIEROTTI CAVITATION ENERGY   =           0.00 KCAL/MOL
> DISPERSION FREE ENERGY       =           0.00 KCAL/MOL
> REPULSION FREE ENERGY        =           0.00 KCAL/MOL
> TOTAL INTERACTION            =          -2.20 KCAL/MOL
> TOTAL FREE ENERGY IN SOLVENT =      -63020.79 KCAL/MOL

>In fact in PCM calculation no vibrational analysis is done so I wonder why the term should be called free energy and what are the H(0) and V/2 operators ?
>
>
>Sincerely Yours
>D.
>
>
>
>
>
>On Thu Feb 20 '14 7:49pm, Alex Granovsky wrote
>----------------------------------------------
>>Dear David,

>>>many thanks for your help and reading the forum in details. It's your great favor.

>>You are welcome.

>>>yes, it has such terms since if I understand well it was proposed by FF to calculate free energy in gas then compare it with the free energy of the system in solvent.

>>> NOTE THAT THE FREE ENERGY IN GAS PHASE IS NOT EQUAL TO
>>> THE -INTERNAL ENERGY IN SOLVENT- WHICH WAS USED TO COMPUTE
>>> VARIOUS QUANTITIES AND CONTRIBUTIONS ABOVE. THIS MEANS
>>> THAT YOU NEED TO PERFORM SEPARATE GAS-PHASE CALCULATIONS
>>> TO COMPUTE FREE ENERGY IN GAS PHASE AND GET ENERGY CHANGE
>>> WHEN GOING FROM THE GAS PHASE TO SOLUTION
>>>

>>>yes it seems that the free energy in solvent doesn't contain translational, rotational, and vibrational terms of Gibbs free energy. So the question that is arising from that is why we do call it free energy and why FF does propose to calculate free energy in gaseous state. Is that free energy something else ?
>>>
>>
>>
>>Many thanks for reporting this problem. I have changed the text
>>of this message to be more correct. Actually the words "FREE ENERGY"
>>should be replaced by just "ENERGY" or "INTERNAL ENERGY". Now the
>>message is:

>>

 NOTE THAT THE ENERGY IN GAS PHASE IS NOT EQUAL TO
 THE -INTERNAL ENERGY IN SOLVENT- WHICH WAS USED TO COMPUTE
 VARIOUS QUANTITIES AND CONTRIBUTIONS ABOVE. THIS MEANS
 THAT YOU NEED TO PERFORM SEPARATE GAS-PHASE CALCULATIONS
 TO COMPUTE ENERGY IN GAS PHASE AND GET ENERGY CHANGE
 WHEN GOING FROM THE GAS PHASE TO SOLUTION

>>I'm sorry for any confusion or misunderstanding the old message could
>>cause.

>>Kind regards,
>>Alex

>>>
>>>
>>>Sincerely Yours,
>>>David
>>>

[ This message was edited on Wed Feb 26 '14 at 3:00am by the author ]