From chemistry-request@ccl.net Wed Sep 25 03:06:53 1991 To: CHEMISTRY@ccl.net Organization: University of Illinois at Chicago Date: Wednesday, 25 Sep 1991 01:30:06 CDT From: Prasad Ravi Subject: Need data on benzene-methane binary mixtures Status: R I am working on calculating the internal contributions to the thermal conductivity of polyatomic mixtures using non-equilibrium molecular dynamics and was wondering if there is any thermodynamic/transport property data available for the benzene-methane mixture, so I could check my simulation results. Does anyone know of the existence of such data?? Thanks a lot for your help!! Prasad Ravi Chemical Engineering University of Illinois at Chicago EMail: U21709@UICVM.CC.UIC.EDU From chemistry-request@ccl.net Wed Sep 25 10:13:00 1991 Date: Wed, 25 Sep 91 10:06:18 EST From: Marcelo Giordan Santos Subject: Natural Orbitals in GAUSSIAN To: chemistry@ccl.net Status: R Does anybody know if it is possible to get Natural Orbitals from any correlation option of GAUSSIAN-88 packge ? I've read the manual, but it seens to have nothing about this. Thanks, Marcelo Giordan. e-mail: marcelo@iqm.unicamp.ansp.br From chemistry-request@ccl.net Wed Sep 25 17:13:49 1991 Date: Wed, 25 Sep 91 13:45:45 PLT From: 97748509@WSUVM1.CSC.WSU.EDU Subject: help for HOMO and LUMO precision To: chemistry@ccl.net Status: R Hello, netters! I am trying to extract HOMO and LUMO values from GAUSSIAN output. The problem is when different basis sets are used, there will be huge difference for the results. The molecules I tried were water and methanol. Can anybody help me figure out why? Is there any better softwere to use for this purpose? P.S.: Since GAUSSIAN cannot do computations on big molecules, I move MOPAC will be my next choice. Then, are the HOMO and LUMO values from MOPAC acceptable, comparing with those from GAUSSIAN? Thanks W. Philip Leigh (1) 97748509@WSUVM1.CSC.WSU.EDU (2) wlei@yoda.eecs.wsu.edu From chemistry-request@ccl.net Wed Sep 25 22:36:29 1991 Date: Wed, 25 Sep 91 21:10:04 EDT From: m10!frisch@uunet.UU.NET (Michael Frisch) Subject: Re: help for HOMO and LUMO precision To: chemistry@ccl.net Status: RO Hello, netters! I am trying to extract HOMO and LUMO values from GAUSSIAN output. The problem is when different basis sets are used, there will be huge difference for the results. The molecules I tried were water and methanol. Can anybody help me figure out why? Is there any better softwere to use for this purpose? P.S.: Since GAUSSIAN cannot do computations on big molecules, I move MOPAC will be my next choice. Then, are the HOMO and LUMO values from MOPAC acceptable, comparing with those from GAUSSIAN? Thanks W. Philip Leigh (1) 97748509@WSUVM1.CSC.WSU.EDU (2) wlei@yoda.eecs.wsu.edu The values of the orbitals evaluated at specific points in space change only moderately with basis set; the values of the coefficients depend on the basis functions -- clearly, when you go from minimal basis to double-zeta, each coefficient of an MBS orbital is replaced by coefficients of two orbitals. These coefficients will vary depending how the relative sizes of the two basis functions and how tight or diffuse the MO would like to be (given the flexability which is not present in a minimal basis). If the minimal basis is particularly poor for a molecule (for example, an anion, for which the orbitals may be much different in size from the fixed size imposed by a minimal basis), then the orbitals will change qualitatively. As for "big molecules", that depends on your definition of big. Of course, semi-empirical methods are cheap and applicable to bigger systems than ab initio. On the other hand, it is routine to do a couple of dozen atoms and several hundred basis functions on modern workstations with Gaussian 90, especially if you just want to look at orbitals. So there's a fair amount you can do ab initio. Semi-empirical methods constrain you to a minimal basis. That avoids the complications of interpreting results from larger basis sets, but it also means you don't have the flexability of better calculations if that's what you need. I would suggest making the choice between ab initio and semi-empirical methods on the basis of whether the semi-empirical methods are reliable for the problems you're interested in. For stable structures of neutral molecules involving the atoms for which lots of parametrization information is available (H, C, N, and O) you will find that the STO-3G MO's and the AM1 MOs are indeed very similar (provided that you interpret the raw AM1 MO coefficients as coefficients of symmetrically orthogonalized AOs, as Gaussian does before printing AM1 orbitals). If you're primarily interested in orbitals for this type of system, there isn't much point in doing STO-3G -- you can either do AM1 (which is as good and cheaper) or Hatree-Fock with a larger basis set (which is more accurate). The farther you stray from the regime for which the semi-empirical method was parametrized, the more you need to concern youself with its reliability. Michael Frisch Gaussian, Inc. ------- From chemistry-request@ccl.net Thu Sep 26 11:03:17 1991 Date: Thu, 26 Sep 1991 09:56 CDT From: Andy Holder Subject: Nobel Prizers To: CHEMISTRY@ccl.net Status: R How about Michael Dewar for a Nobel Prize? An uninterested observed, Andy Holder =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= DR. ANDREW HOLDER Department of Chemistry || BITNET Addr: AHOLDER@UMKCVAX1 University of Missouri - Kansas City || Internet Addr: aholder@vax1.umkc.edu Spencer Chemistry, Room 502 || Phone Number: (816) 235-2293 Kansas City, Missouri 64110 || FAX Number: (816) 235-1717 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=