From chemistry-request@ccl.net Fri May 1 02:33:27 1992 Date: Thu, 30 Apr 1992 23:37 EST From: "DOUGLAS A. SMITH" Subject: basis set effects on virtual orbitals To: chemistry@ccl.net Status: RO I have a general question for those of you who use a variety of basis sets for ab initio quantum calculations. Suppose you were to do a study of a particular molecule or homologous series of molecules, and you did a study as a function of basis set. Would you expect to see a change in the ordering of the virtual orbital symmetries as a function of energy? If so, what basis sets or types of functions would cause such a change? Or would this change be due to the type of calculation, e.g. single determinant versus multiconfigurational approach? I would prefer to see this discussion on the open net, although I will summarize those answers I receive directly. Doug Smith Assistant Professor of Chemistry The University of Toledo Toledo, OH 43606-3390 voice 419-537-2116 fax 419-537-4033 email fax0236@uoft02.utoledo.edu From chemistry-request@ccl.net Fri May 1 10:04:06 1992 Date: Fri, 01 May 92 08:49:20 EDT From: Janet Del Bene Subject: Response to Doug Smith To: chemistry@ccl.net Status: RO Doug, The addition of diffuse functions to the basis set gives rise to low-energy virtual orbitals. Janet E. Del Bene From chemistry-request@ccl.net Fri May 1 14:21:54 1992 Date: Fri, 01 May 1992 11:28:07 EDT From: nancyb@XRAY.CHEM.RPI.EDU (Nancy O. Buswell) Subject: equipment for sale To: chemistry@ccl.net Status: RO Dear Netters, My lab has a Silicon Graphics IRIS 3120, approximately 5 years old, which does need some repair. If anyone would be interested in this for salvage purposes or parts, please let me know right away. It is located at Rensselaer Polytechnic Institute in Troy, NY. Thank you. Nancy Buswell nancyb@xray.chem.rpi.edu From chemistry-request@ccl.net Fri May 1 15:32:21 1992 Date: Fri, 1 May 1992 12:37 EST From: "To help us serve you better, please take a number..." Subject: virtual orbitals To: chemistry@ccl.net Status: RO Doug, I would be cautious about using virtual orbitals from HF SCF calculations, since the variation is done on the occupied orbitals they are 'better' than the virtual MOs. If I recall the classic example, electron affinities from Koopmans theorem are worse than ionization potentials. Michelle M. Francl Bryn Mawr College From chemistry-request@ccl.net Fri May 1 16:41:09 1992 Date: 1 May 92 12:30 LCL From: PA13808%UTKVM1.BITNET@OHSTVMA.ACS.OHIO-STATE.EDU Subject: BITNET mail follows To: CHEMISTRY@ccl.net Status: RO Role of basis functions and symmetry. I am not sure I understand the question, but here are some factors to consider. First the make up of virtual orbitals is determined by two requirements. They must be orthogonal to the occupied orbitals and to each other.If you add extra functions which have a different symmetry than the ones already present they could apear;above,inbetween or below the valence or antibonding manifold. If you add lots of very diffuse functions they will probably be above the antibonding mos . then they will depress those of the same symmetry and leave the others alone. If you have a molecule with low lying RYDBERG states these are usually described by adding suitable diffuse functions which will then be beloww the antibonding valence manifold. Then if they mix much then because of orthogonality they will push up the valence virtual orbitals of the same symmetry. The only way to really tell is to look at the LCAO make up of your virtual MO, particularly if you have a basis set which describes states, they could be anywhere! John E. BLOOR(PA13808 AT UTKVM1) From chemistry-request@ccl.net Fri May 1 18:29:21 1992 Date: Fri, 1 May 92 15:23 EDT From: SML108@PSUVM.PSU.EDU Subject: Re: equipment for sale To: nancyb@XRAY.CHEM.RPI.EDU Status: RO Hi, how goes things? Alas the poor old 3120 finally bites the dust, eh? Are you replacing it with anything better or is that a lost cause now? Scott From chemistry-request@ccl.net Fri May 1 19:36:21 1992 Date: Fri, 1 May 92 15:12:25 EDT From: curtis@libra.wistar.upenn.EDU (curtis wahlgren) Subject: equipment for sale To: nancyb@XRAY.CHEM.RPI.EDU Status: RO Dear Mrs. Buswell I am interested but I am going to have to take this up with my boss here at Wistar. Can you give me some more information on the IRIS machine? Do you just want someone to come and cart it away or do you want some money for it? What shape is it in? Is the monitor in good working condition? Please let me know so I can give my boss all the facts. Thank you. Curtis Wahlgren curtis@libra.wistar.upenn.edu From chemistry-request@ccl.net Fri May 1 20:17:00 1992 Date: Fri, 1 May 92 16:52:24 EDT From: gene@eastrg2.cray.COM (Eugene Fleischmann) Subject: CO Potential To: chemistry@ccl.net Status: RO Dear Secrest, Unfortunately, you don't say for what purpose you need the potential energy surface for CO, so I can't tell whether this suggestion will have sufficient accuracy. Morse potentials for ground state CO and for an ad hoc excited state were published for a classical dynamics study of atom recombination on single crystal platinum; E.D.Fleischmann and J.E.Adams, Surface Science, 193 (1988) 593 and earlier J.Tully, Journal of Chemical Physics, 73 (1980) 6333. Good luck. Gene Fleischmann