From owner-chemistry@ccl.net Tue May 14 10:23:00 2013 From: "Scott Mckechnie jsm78|,|cam.ac.uk" To: CCL Subject: CCL: Orbital energies for neutral and cation species in vacuum and solution Message-Id: <-48681-130514095305-21698-DUxjutQWQLGgcy5ZkTtgow++server.ccl.net> X-Original-From: "Scott Mckechnie" Date: Tue, 14 May 2013 09:53:04 -0400 Sent to CCL by: "Scott Mckechnie" [jsm78]-[cam.ac.uk] I am looking into the change in orbital energies upon vertical ionization (i.e. ignoring nuclear reorganization) for molecules in vacuum and in solution. First of all in vacuum, I modelled the removal of an electron by performing a DFT single-point energy calculation (on the neutral closed shell ground state gas phase optimized geometry) with charge and multiplicity '12'. The single-point calculation output file noted that there are now 74 beta electrons and so am I right in saying that the first virtual beta orbital is the orbital from which the electron was removed? This orbital energy (-8.76 eV) is much lower than the highest occupied orbital energy (-5.81 eV) in the neutral molecule. However, performing the same calculation in solution (with an implicit solvent model) gives a highest occupied orbital energy of -5.65 eV for the neutral molecule and a first virtual beta orbital energy of -5.40 eV for the cation. So, in vacuo you have a drop in the orbital energy but in solution the energy is raised. Is this a result of the solvent having a larger effect on the energetics than the increase in positive charge? Best wishes, Scott jsm78^^cam.ac.uk From owner-chemistry@ccl.net Tue May 14 13:05:00 2013 From: "Johannes Hachmann jh*chemistry.harvard.edu" To: CCL Subject: CCL: Orbital energies for neutral and cation species in vacuum and solution Message-Id: <-48682-130514114557-1437-8teP1pLOtMmKbNL5aCd0IA++server.ccl.net> X-Original-From: "Johannes Hachmann" Content-Language: en-us Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset="us-ascii" Date: Tue, 14 May 2013 11:45:40 -0400 MIME-Version: 1.0 Sent to CCL by: "Johannes Hachmann" [jh^chemistry.harvard.edu] Hi Scott, > file noted that there are now 74 beta electrons and so am I right in saying that > the first virtual beta orbital is the orbital from which the electron was > removed? Yes. BTW: Did you set up your delta-SCF as restricted open shell or unrestricted? Depending on the molecule you study it may be worth to compare the two approaches. In each case you should be consistent though, and make sure that you interpret any spin-polarized results carefully. > This orbital energy (-8.76 eV) is much lower than the highest occupied orbital > energy (-5.81 eV) in the neutral molecule. Interpreting KS eigenvalues - in particular for virtuals is a tricky business. You should check out, e.g., Zhang, G.; Musgrave, C. B. Comparison of DFT Methods for Molecular Orbital Eigenvalue Calculations. J. Phys. Chem. A 2007, 111, 1554-1561. Stowasser, R.; Hoffmann, R. What Do the KohnSham Orbitals and Eigenvalues Mean?. J. Am. Chem. Soc. 1999, 121, 3414-3420. Hamel, S.; Duffy, P.; Casida, M. E.; Salahub, D. R. Kohn Sham Orbitals and Orbital Energies: Fictitious Constructs but Good Approximations All the Same. J. Electron Spectrosc. Relat. Phenom. 2002, 123, 345-363. Chong, D. P.; Gritsenko, O. V.; Baerends, E. J. Interpretation of the KohnSham Orbital Energies as Approximate Vertical Ionization Potentials. J. Chem. Phys. 2002, 116, 1760-1772. Luo, J.; Xue, Z. Q.; Liu, W. M.; Wu, J. L.; Yang, Z. Q. Koopmans' Theorem for Large Molecular Systems within Density Functional Theory. J. Phys. Chem. A 2006, 110, 12005-12009. Zhan, C.-G.; Nichols, J. A.; Dixon, D. A. Ionization Potential, Electron Affinity, Electronegativity, Hardness, and Electron Excitation Energy: Molecular Properties from Density Functional Theory Orbital Energies. J. Phys. Chem. A 2003, 107, 4184-4195. > This orbital energy (-8.76 eV) is much lower than the highest occupied orbital > energy (-5.81 eV) in the neutral molecule. This is not really unexpected because the Fock operator is rather different in the two cases. Also note the difference of occupied and virtual orbitals in the DFT framework. > So, in vacuo you have a drop in the > orbital energy but in solution the energy is raised. Is this a result of the solvent > having a larger effect on the energetics than the increase in positive charge? It's a bit more complicated than that. Check out this discussion: http://jcp.aip.org/resource/1/jcpsa6/v130/i4/p044107_s1 I hope this helps. Best wishes over to Cambridge Johannes ----------------------------------------------- Dr. Johannes Hachmann Research Associate Harvard University Department of Chemistry and Chemical Biology 12 Oxford St, Rm M104A Cambridge, MA 02138 ----------------------------------------------- > -----Original Message----- > From: owner-chemistry+jh==chemistry.harvard.edu[]ccl.net [mailto:owner- > chemistry+jh==chemistry.harvard.edu[]ccl.net] On Behalf Of Scott Mckechnie > jsm78|,|cam.ac.uk > Sent: Tuesday, 14 May, 2013 09:53 > To: Hachmann, Johannes > Subject: CCL: Orbital energies for neutral and cation species in vacuum and > solution > > > Sent to CCL by: "Scott Mckechnie" [jsm78]-[cam.ac.uk] I am looking into the > change in orbital energies upon vertical ionization (i.e. ignoring nuclear > reorganization) for molecules in vacuum and in solution. First of all in vacuum, I > modelled the removal of an electron by performing a DFT single-point energy > calculation (on the neutral closed shell ground state gas phase optimized > geometry) with charge and multiplicity '12'. The single-point calculation output > file noted that there are now 74 beta electrons and so am I right in saying that > the first virtual beta orbital is the orbital from which the electron was > removed? > > This orbital energy (-8.76 eV) is much lower than the highest occupied orbital > energy (-5.81 eV) in the neutral molecule. However, performing the same > calculation in solution (with an implicit solvent model) gives a highest occupied > orbital energy of -5.65 eV for the neutral molecule and a first virtual beta > orbital energy of -5.40 eV for the cation. So, in vacuo you have a drop in the > orbital energy but in solution the energy is raised. Is this a result of the solvent > having a larger effect on the energetics than the increase in positive charge? > > Best wishes, > > Scott > jsm78.[].cam.ac.ukTo > recover the email address of the author of the message, please change the > strange characters on the top line to the [] sign. You can also look up the X- > Original-From: line in the mail header. From owner-chemistry@ccl.net Tue May 14 23:33:00 2013 From: "Ramesh Kumar rameshchitumalla^gmail.com" To: CCL Subject: CCL: Orbital energies for neutral and cation species in vacuum and solution Message-Id: <-48683-130514233032-780-lAYADWMKX57yRq13EUle9A++server.ccl.net> X-Original-From: Ramesh Kumar Content-Type: text/plain; charset=ISO-8859-1 Date: Wed, 15 May 2013 09:00:26 +0530 MIME-Version: 1.0 Sent to CCL by: Ramesh Kumar [rameshchitumalla(a)gmail.com] Dear Scott, The reply from Dr. Johannes Hachmann is really very useful. The orbital energy of a cation is much lower than that of its corresponding neutral molecule and again it comes very near to the case similar to neutral molecule in the presence of a polar solvent. For some numbers you can see CPL 396 (2004) 43-48. -- With Best Regards: CH. Ramesh Kumar Senior Research Fellow, Computational Chemistry Lab, Indian Institute of Chemical Technology(IICT), Tarnaka, Hyderabad.