From owner-chemistry@ccl.net Thu Feb 12 17:39:01 2015 From: "Mariusz Radon mariusz.radon-x-gmail.com" To: CCL Subject: CCL:G: Fermi coupling constants for singlet AF states Message-Id: <-51023-150212173633-7074-Ii6yPb8gxhIyaz0VVN9jCA#server.ccl.net> X-Original-From: Mariusz Radon Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset=ISO-8859-1 Date: Thu, 12 Feb 2015 23:36:25 +0100 MIME-Version: 1.0 Sent to CCL by: Mariusz Radon [mariusz.radon#%#gmail.com] On 02/10/2015 11:58 PM, Gennady L Gutsev gennady.gutsev[]famu.edu wrote: > Sent to CCL by: "Gennady L Gutsev" [gennady.gutsev%%famu.edu] > Good afternoon, > we got a problem with interpreting the results of calculations > of Fermi contact coupling constants for antiferromagnetic > singlet states. Generally, a singlet cannot be seen in ESR > experiments because the hyperfine coupling SAI should > be zero if S = 0. > (...) > 2S+1 = 1 > Mulliken atomic spin densities: > 1 Mn 0.100879 > 2 Al -0.100879 > Isotropic Fermi Contact Couplings > Atom a.u. MegaHertz Gauss 10(-4) cm-1 > 1 Mn(55) 0.75916 419.56836 149.71242 139.95294 > 2 Al(27) 0.03470 20.22439 7.21657 6.74613 > > That is, the singlet state has non-zero Fermi coupling constants (because > there are excess spin sensities on atoms). But this singlet is considered > to be not seen in ESR experiments. > Now, the question is what Gaussian09 actually computes for AF singlet state? > and how it can be related to ESR experiments? > Dear Gennady: I am not sure if I understood your question correctly. I suppose that the Fermi coupling constants computed for the AF "singlet" state from broken-symmetry DFT calculations are as unphysical as the spin densities themselves. For the pure singlet state (2S+1=1) the spin density should be zero everywhere in space. The reason why spin densities and Fermi couplings are non-zero in your AF calculations, is that the wave function used (i.e., spin-unrestricted Slater determinant) does not really describe a singlet state, but rather a superposition of a singlet and a triplet state, and possibly higher spin states too. (This is known as spin contamination problem.) So, I believe the non-zero Fermi couplings you get are due to the admixture of the contaminating triplet state (and possibly higher spin states too). > On another hand, the Mn Fermi coupling constant is zero in the > singlet state of MnO4-, > which is right, and there is no excess spin density on the Mn site. > This may happen if your calculations for MnO4- converged to a spin-restricted solution (you can compare the values for your two cases). Still, there could be a spin-unrestricted solution of lower energy. The keyword STABLE may be useful to check if the closed shell singlet solution you captured for MnO4- is really stable or there exists another, spin-unrestricted solution of lower energy. Best regards, M.R. -- Dr Mariusz Radon, Ph.D. Coordination Chemistry Group Faculty of Chemistry Jagiellonian University ul. Ingardena 3, 30-060 Krakow, Poland http://www2.chemia.uj.edu.pl/~mradon From owner-chemistry@ccl.net Thu Feb 12 19:32:00 2015 From: "Scott Brozell sbrozell]^[rci.rutgers.edu" To: CCL Subject: CCL: Announcement: Release of DOCK 6.7 Message-Id: <-51024-150212193015-8777-7XQA3kyJJ6E/9caoklREpQ~!~server.ccl.net> X-Original-From: Scott Brozell Content-Disposition: inline Content-Type: text/plain; charset=us-ascii Date: Thu, 12 Feb 2015 19:30:10 -0500 Mime-Version: 1.0 Sent to CCL by: Scott Brozell [sbrozell###rci.rutgers.edu] We are pleased to announce the release of DOCK 6.7. DOCK is a suite of programs for molecular docking. The source code for DOCK 6.7 is available for download and free for academic users at http://dock.compbio.ucsf.edu/. In version 6.7 the default values for several input parameters were updated based mainly on a performance assessment using large data sets and employing multiple metrics including pose reproduction, cross-docking, and database enrichment. For full information on what is new in DOCK 6.7, please visit: http://dock.compbio.ucsf.edu/DOCK_6/new_in_6.7.txt Sincerely, The DOCK Team Please visit us at the DOCK Web site. http://dock.compbio.ucsf.edu