Author Topic: Thermodynamic properties calculation in solution  (Read 12100 times)

willows9803

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Thermodynamic properties calculation in solution
« on: July 30, 2009, 10:33:48 PM »
Hi guys,

How are you doing?

I'm using Turbomole & Cosmotherm to calculate physico-chemical properties of various compounds and they work very well. However, if I'd like to get the enthalpy, entropy and free energy of a compound, I can only get them in gas phase using "FreeH" module of Turbomole. How can I utilize cosmo to get those thermodynamic data in solution?

Thanks a lot.

willows

jan

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Re: Thermodynamic properties calculation in solution
« Reply #1 on: September 28, 2009, 05:36:22 PM »
The values calculated by freeH only depend on the geometry of the molecule only. These values are calculated via the partition sum of translation,
vibration and rotation and these depend on vibrational modes and moments of rotation. If you try to model solvation by doing a singlepoint calculation
with COSMO the geometry is not altered and the values from freeH are the same in solution. Only the electronic energy changes. You have to add the
electron energy from the COSMO-singlepoint to your chemical potential from freeH to obtain the "absolute" chemical potential in solution. I am not
 familiar with the cosmotherm program but if it does not alter the structure the values from freeH are still valid.

diedenho

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Re: Thermodynamic properties calculation in solution
« Reply #2 on: October 01, 2009, 03:45:03 PM »
Hi Jan,

For properties like the vapor pressure we use the cosmo file as well as the gas phase energy in COSMOtherm.
If you like to combine the gas phase and the solution I would suggest to use the Gibbs free energy of solvation
from COSMOtherm and the gas phase Gibbs free energy from the TURBOMOLE gas phase caulations and freeh.
For the Gibbs free energy of reactions, for instance, we use gas phase DFT frequencies for the chemical
potential in the gas phase (freeh) together with DFT or maybe MP2 etc. gas phase energies. To get back to
the solution you need the Gibbs free energy of solution for all product and educts. You can get this values
from COSMOtherm. As input you need the cosmo files and gas phase energy files, which can be calculated
with TURBOMOLE. The Gibbs free energy of solvation can be calculated via the Henry constant option (Gsolv option).
Please be aware of the different definition of this value (the reference 1bar/1mol solvent should be OK for you).

hope thius helps,
michael


willows9803

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Re: Thermodynamic properties calculation in solution
« Reply #3 on: October 12, 2009, 02:23:35 PM »
Hi michael,

Thank you for your reply.

Are you suggesting to use the gas phase energy, free energy of solvation and chemical potential (free FreeH) together to get the free energy of reaction in solution?

If I need to get the enthalpy of the reaction in solutions, how can I get the enthalpy of solvation from Cosmotherm?

Thanks again.

willows

Hi Jan,

For properties like the vapor pressure we use the cosmo file as well as the gas phase energy in COSMOtherm.
If you like to combine the gas phase and the solution I would suggest to use the Gibbs free energy of solvation
from COSMOtherm and the gas phase Gibbs free energy from the TURBOMOLE gas phase caulations and freeh.
For the Gibbs free energy of reactions, for instance, we use gas phase DFT frequencies for the chemical
potential in the gas phase (freeh) together with DFT or maybe MP2 etc. gas phase energies. To get back to
the solution you need the Gibbs free energy of solution for all product and educts. You can get this values
from COSMOtherm. As input you need the cosmo files and gas phase energy files, which can be calculated
with TURBOMOLE. The Gibbs free energy of solvation can be calculated via the Henry constant option (Gsolv option).
Please be aware of the different definition of this value (the reference 1bar/1mol solvent should be OK for you).

hope thius helps,
michael