From owner-chemistry@ccl.net Thu Apr 6 10:27:00 2017 From: "Uwe Huniar huniar,+,cosmologic.de" To: CCL Subject: CCL: Thermodynamic Data & Solvation - Calculation Questions: Message-Id: <-52727-170406102444-32097-O0pLCxkuFFS+UJQeqEfJSg..server.ccl.net> X-Original-From: Uwe Huniar Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=utf-8; format=flowed Date: Thu, 6 Apr 2017 16:24:18 +0200 MIME-Version: 1.0 Sent to CCL by: Uwe Huniar [huniar~!~cosmologic.de] Hello, some time ago we have been asked similar questions, so I forwarded this issue to our own implicit solvation expert, Frank Eckert. Here his answer (probably not directly an answer to all your questions, though): The topic of reference states is sometimes a bit confusing. The molar reference state of 1 mol/L in both gas and solution is the one that typically is used to compare the computed DGsolv to "experimentally" determined values, while the bar/mol reference state is intended for the use in reaction free energy calculations using the thermodynamic cycle. I have put "experimentally" in quotes, because DGfus is not a direct observable in experiments. DGfus typically is extrapolated from solubility or VLE data via the Henry law constant and the definition of DGsolv depends on a given reference state. This by convention is the molar reference state of 1 mol/L in both gas and solution. The molar convention is also followed by Cramer and Truhlar in their SMx papers. They converted both experimental and calculated DGsolv value to the molar reference frame. The molar reference state is used in most databases and also by most experimentalists, but it is in no way a natural or self-explaining choice. It is just a convention. If you look into original papers from experimentalists, in particular older oner > from Russia or China, you might as well also find other reference states. Here is s link to a recent publication that tries to unravel some of the confusion: http://onlinelibrary.wiley.com/doi/10.1002/aic.15716/full Hope this helps a bit, Uwe Am 06.04.2017 um 08:24 schrieb MIELCZAREK Detlev Conrad detlev-conrad.mielczarek-.-ifpen.fr: > > Sent to CCL by: MIELCZAREK Detlev Conrad [detlev-conrad.mielczarek]^[ifpen.fr] > Dear CCL, a question on thermodynamic data & solvation from me, maybe you can help me. > > So, the basic problem for me is, that I am calculating/want to calculate thermodynamic data (Hf, S - hence also dG) in solvation, using implicit solvation models, SMD with a COSMO cavity to be specific. For my application, these should be accurate enough. (So no molecular dynamics simulations etc.) > > Solvation models are normally parametrised for dGsolv - so this value can be extracted from the quantum chemistry calculation as the difference in the calculated Gibbs Free Enthalpy. > Hf can calculated easily in the gas phase, and a re-optimisation of the structure with solvation should capture the majority of the impact of solvation on the enthalpy. (Which is dominated by molecular structure.) > (I guess there is the case of stabilisation and complexes, such as are reported for water. However this is currently beyond the scope of my work.) > > The topic of solvation has been discussed previously on the CCL here: > http://www.ccl.net/chemistry/resources/messages/2011/12/01.001-dir/ > http://www.ccl.net/chemistry/resources/messages/2011/10/06.005-dir/ > http://www.ccl.net/chemistry/resources/messages/2014/05/01.004-dir/ > And there is the book "Essentials of Computational Chemistry Theories and Models" from Professor Cramer with a section on phase change (the source of my confusion). > > Specifically, the discussion concerning the energy change related to the state conversion causes me some grief. > > On the one hand, the CCL responses read as if this should be applied in the case of any phase change, but then others suggest this is applicable only if the process is a second order reaction and thus the total number of mols changes? - The latter view seems to agree with the book... > > So if I have compound A in both the gas and liquid phase (from a quantum chemistry calculation), do I need to account for the phase change/change of state or not? Or is it something that can be included in the parametrisation of the solvation model/the quantum chemistry code already? > > Just to add more confusion to the topic: I have trialled a commercial product which gives the Gibbs Enthalpy of Solvation in kcal/mol for mol/L concentrations and using a very low end/fast functional, it gives values similar to when a correction term is added... on the other hand, where available, the calculated values without correction agree with the published values in the SMD paper: http://pubs.acs.org/doi/abs/10.1021/jp810292n (Supplementary Data) > > In addition, a regular computational chemistry calculation sees very little (virtually no) difference in the entropy between the gaseous and solvated phase. This would agree with the CCL-linked paper here http://pubs.acs.org/doi/abs/10.1021/jp205508z . But this would clash with the common expectation that entropy in the liquid phase is reduced... > > Hence, I would highly appreciate if someone knowledgeable in the field of solvation could guide me onto the correct track. > > Detlev Conrad Mielczarek > Scientific Visitor/Post Doctorant > IFP Energies nouvelles > France > > www.ifpenergiesnouvelles.fr > > __________________________ > Avant d'imprimer, pensez à l'environnement ! Please consider the environment before printing ! > Ce message et toutes ses pièces jointes sont confidentiels et établis à l'intention exclusive de ses destinataires. Toute utilisation non conforme à sa destination, toute diffusion ou toute publication, totale ou partielle, est interdite, sauf autorisation expresse. IFP Energies nouvelles décline toute responsabilité au titre de ce message. This message and any attachments are confidential and intended solely for the addressees. Any unauthorised use or dissemination is prohibited. IFP Energies nouvelles should not be liable for this message. > __________________________> > > -- -------------------- Dr. Uwe Huniar COSMOlogic GmbH & Co. KG Imbacher Weg 46 D-51379 Leverkusen, Germany phone +49-2171-363668 fax +49-2171-731689 e-mail turbomole:cosmologic.de web www.cosmologic.de HRA 20653 Amtsgericht Koeln, GF: Dr. Andreas Klamt Komplementaer: COSMOlogic Verwaltungs GmbH HRB 49501 Amtsgericht Koeln, GF: Dr. Andreas Klamt