From owner-chemistry@ccl.net Thu Apr 6 02:28:00 2017 From: "MIELCZAREK Detlev Conrad detlev-conrad.mielczarek-.-ifpen.fr" To: CCL Subject: CCL: Thermodynamic Data & Solvation - Calculation Questions: Message-Id: <-52726-170406022507-27941-XpARDww3LCHSxvCrIscM0g[-]server.ccl.net> X-Original-From: MIELCZAREK Detlev Conrad Content-Language: en-US Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="utf-8" Date: Thu, 6 Apr 2017 06:24:59 +0000 MIME-Version: 1.0 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. __________________________