CCL: Thermodynamic Data & Solvation - Calculation Questions:



 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
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