From owner-chemistry@ccl.net Fri Aug 10 11:50:01 2012 From: "DJUKIC Jean-Pierre djukic]*[unistra.fr" To: CCL Subject: CCL: Approximation of the dielectric constant of a binary solvent mixture Message-Id: <-47357-120810113216-31998-aJeq1lbrZLMLtbyzuefOHA()server.ccl.net> X-Original-From: DJUKIC Jean-Pierre Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-1; format=flowed Date: Fri, 10 Aug 2012 17:31:45 +0200 MIME-Version: 1.0 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. From owner-chemistry@ccl.net Fri Aug 10 13:26:00 2012 From: "John McKelvey jmmckel+/-gmail.com" To: CCL Subject: CCL: Approximation of the dielectric constant of a binary solvent mixture Message-Id: <-47358-120810132346-531-d3nIV0Yg22fYFJjKtrB6kw!A!server.ccl.net> X-Original-From: John McKelvey Content-Type: text/plain; charset=ISO-8859-1 Date: Fri, 10 Aug 2012 13:23:38 -0400 MIME-Version: 1.0 Sent to CCL by: John McKelvey [jmmckel#gmail.com] My experience shows that in COSMO that changes in solvent radius does not have a significant effect. At least in the MOPAC codes I have the same solvent radius is used for all solvents. The solvent radius seems to be used for mapping out the solute radius. If you can input the radius in the code you are using try a radius of 0.1 - 0.25. The default radius is usually the radius of H, around 1. Regards, John McKelvey On Fri, Aug 10, 2012 at 11:31 AM, DJUKIC Jean-Pierre djukic]*[unistra.fr wrote: > > 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/> > -- John McKelvey 10819 Middleford Pl Ft Wayne, IN 46818 260-489-2160 jmmckel#%#gmail.com