From owner-chemistry@ccl.net Sat Aug 11 02:56:01 2012 From: "Andreas Klamt klamt .. cosmologic.de" To: CCL Subject: CCL: Approximation of the dielectric constant of a binary solvent mixture Message-Id: <-47359-120811024728-31521-0R3agrqJ/SLf/diR5qL7hg===server.ccl.net> X-Original-From: Andreas Klamt Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=ISO-8859-1; format=flowed Date: Sat, 11 Aug 2012 08:47:18 +0200 MIME-Version: 1.0 Sent to CCL by: Andreas Klamt [klamt-x-cosmologic.de] Dear Jean-Pierre, it is one of the most severe shortcomings of dielectric continuum models that they cannot describe the difference of protic and aprotic solvents, e.g. with identical epsilon. That was one of my motivations to develop COSMO-RS, COSMO for realistic solvation already in 1995(!!!), i.e. just 2 years after I invented COSMO. Fudging the radii in a dielectric continuum model in order to describe that effect is black magic. Read about COSMO-RS. COSMO-RS also has the full concept of mixture thermodynamics and temperature dependence. What kind of properties are you interested in? For equilibrium constants you can use standard COSMO-RS, if you want response properties, you need direct-COSMO-RS (available in TURBOMOLE and ORCA). Best regards Andreas Am 10.08.2012 17:31, schrieb DJUKIC Jean-Pierre djukic]*[unistra.fr: > > Sent to CCL by: DJUKIC Jean-Pierre [djukic!^!unistra.fr] > Dear listers, > > I need to do a quick COSMO-DFT calculation for a molecular system > dipped into a binary mixture of ( miscible ;) ) polar (1) and apolar > (2) solvents. > > I have read that one could approximate the resulting epsilon12 value > of the solvent mixture by the following formula > > ln(epsilon12)= x1ln(epsilon1) + x2ln(epsilon2) where x is the molar > fraction of each component of the mixture. > > This sounds reasonable to me (but perhaps not to a specialist ...), > the question is now how to approximate the equivalent solvent radius > for such a mixture...if relevant( because it is obviously an important > parameter in COSMO)? I would be tempted to keep the value of the > major component of the mixture...but I feel like juggling with > swords... what happens to the "solvent radius" parameter if x1=x2 ? > > > > Jean-Pierre.http://www.ccl.net/chemistry/sub_unsub.shtmlConferences: > http://server.ccl.net/chemistry/announcements/conferences/> > > -- Prof. Dr. Andreas Klamt CEO / Geschäftsführer COSMOlogic GmbH & Co. KG Burscheider Strasse 515 D-51381 Leverkusen, Germany phone +49-2171-731681 fax +49-2171-731689 e-mail klamt.:.cosmologic.de web www.cosmologic.de [University address: Inst. of Physical and Theoretical Chemistry, University of Regensburg] Join us at the 4th-COSMO-RS-Symposium April 2013 Details at www.cosmologic.de/symposium2013 HRA 20653 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt Komplementaer: COSMOlogic Verwaltungs GmbH HRB 49501 Amtsgericht Koeln, GF: Prof. Dr. Andreas Klamt