From thuber@Physik.TU-Muenchen.DE Thu Feb 2 08:41:45 1995 Received: from srv.cip.physik.tu-muenchen.de for thuber@Physik.TU-Muenchen.DE by www.ccl.net (8.6.9/930601.1506) id IAA08381; Thu, 2 Feb 1995 08:08:46 -0500 Received: from speedy.cip.physik.tu-muenchen.de by srv.cip.physik.tu-muenchen.de with SMTP id AA01360 for (5.67a/IDA-1.5/bs04); Thu, 2 Feb 1995 14:07:19 +0100 Received: by speedy.cip.physik.tu-muenchen.de (4.1/SMI-4.1) id AA25541; Thu, 2 Feb 95 14:07:19 +0100 Date: Thu, 2 Feb 95 14:07:19 +0100 From: Thomas.Huber@Physik.TU-Muenchen.DE Message-Id: <9502021307.AA25541@speedy.cip.physik.tu-muenchen.de> To: CHEMISTRY@ccl.net Subject: Summary: van der Waals parameters from ab initio calc 10 days ago I submitted the following question to CCL, the answers I got are appeded: Subject: van der Waals parameters from ab initio calc? Hi netters! Could you please tell me how to derive van der Waals parameters from ab initio calculations! Any suggestions are wellcome (references, principles,...). I'm interested in practical as well as theoretical approaches to this problem. If I got interesting response, I'll collect them and post it to this group! Thank you for help! Thomas Thomas Huber Institut fuer Physikalische Biochemie der Universitaet Muenchen Schillerstrasse 44 80336 Muenchen Germany email: thuber@physik.tu-muenchen.de Return-Path: YQIN@aardvark.ucs.uoknor.edu Dear Huber: Thank you for posting such interesting question. Eventhough I can not give you answer, but I would like to see the summary if you can get enough. Thank you very much in advarce With my best regards yuli qin yqin@aardvark.ucs.uoknor.edu From: jxh@ibm12.biosym.com (Joerg Hill) Hi, sorry for wasting bandwidth, but a direct response did not work. Van-der-Waals parameters for repulsion can be obtained from ab initio calculations using a test particle ansatz. The most papers have been published by Ahlrichs: H.-J. Boehm, R. Ahlrichs: JCP 77 (1982) 2028 H.-J. Boehm, R. Ahlrichs, P. Scharf, H. Schiffer: JCP 81 (1984) 1389 are the both basic paper. Applications can be found in: H.-J. Boehm, C. Meissner, R. Ahlrichs: Mol. Phys. 53 (1984) 651 K. P. Sagarik, R. Ahlrichs, S. Brode: Mol. Phys. 57 (1986) 1247 K. P. Sagarik, R. Ahlrichs: Chem. Phys. Letters 131 (1986) 74 K. P. Sagarik, R. Ahlrichs: JCP 86 (1987) 5117 J.-R. Hill, J. Sauer: JPC 98 (1994) 1238 A new paper, which considers anisotropy is: A. J. Stone, C.-S. Tong: JCC 15 (1994) 1377 I don't know any papers concerning the derivation of dispersive parameters from ab initio calculations. But dispersion requires electron correlation and since these calculations are rather expensive, it could be that noone has triesd it so far. Density Functional calculations could change this. Tschuess Joerg P.S.: host name Physik.TU-Muenchen.DE NOT FOUND. -------------------------------------------------------------------------------- Dr. Joerg-Ruediger Hill | Every attempt to employ mathematical methods in the Biosym Technologies, Inc. | study of chemical questions must be considered pro- 9685 Scranton Road | foundly irrational and contrary to the spirit of San Diego, CA 92121-2777 | chemistry ... If mathematical analysis should ever USA | hold a prominent place in chemistry - an aberration | which is happily almost impossible - it would Phone (619) 546-5508 | occasion a rapid and widespread degeneration of Fax (619) 458-0136 | that science. E-mail jxh@biosym.com | A. Comte, 1830 -------------------------------------------------------------------------------- The opinions expressed in this message are my personal opinions and no offical statements of Biosym Technologies, Inc. For informations about Biosym products send mail to: rcenter@biosym.com. -------------------------------------------------------------------------------- Return-Path: helden@gaucho.ucsb.edu Servus, We are interested in the ineraction of helium with small to medium small (10 - 200 atoms) molecules. We found that with the MM3 vdW parameters (Theochem, 312 (1994) 69), we can reproduce our experimental results (gas phase mobilities) very well. I also tried to calculate vdW parameters for He-He and H3C-H - He. In order to get the attractive part of the potential right, one has to throw in a lot of correlation (CCSD(t)) and large basis sets (tripple zeta+pol.+diffuse). The repulsive part of the potential on the other hand is well described by plain SCF + small basis set. I did a scan of the pot. surface of H3C-H - He and found that fitting a 12-6 potential to the scan gives very poor agreement while an exp.-6 potential is much better. The well depth and the position for these two systems seems to be in reasonable good agreement with the MM3 parameters. Contact me if you want to know more about what we are doing, ....Gert ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ + Gert von Helden, Dept. of Chemistry, UCSB, Santa Barbara, CA 93106 + + Tel : 805-893-2673, Fax : 805-893-8703 + + E-mail: helden@gaucho.ucsb.edu + ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ Return-Path: states@ibc.wustl.edu |> Thomas Huber wrote: |> Could you please tell me how to derive van der Waals parameters from |> ab initio calculations! |> Any suggestions are wellcome (references, principles,...). For condensed matter, there is a fundamental problem with the derivation of non-bonded interactions from ab initio calculations on isolated molecules. High quality ab initio calculations include wavefunctions with quite large spatial extents, much larger than existence in a condensed matter environment would allow. So, if you are going to calculate non-bonded interactions, you need to start with realistic calculations including multiple molecules. The energy of interaction is straightforward. Deciding how much of it is "van der Waals" is another issue. David States From: underhil@hp.rmc.ca (Ross Underhill) Subject: Re: CCL:van der Waals parameters from ab initio calc? >Could you please tell me how to derive van der Waals parameters from ab initio >calculations! >Any suggestions are wellcome (references, principles,...). >I'm interested in practical as well as theoretical approaches to this problem. >If I got interesting response, I'll collect them and post it to this group! A very interesting question and one I have tried to deal with myself. For some elements you can put together two diatomics and bring them together using ab initio calcs and plot the total energy. You can then fit the calculated energy as a function of separation. I have done this in a few cases. I've even done it for methane. You really should do it using UHF since a lot of the attraction at long distances has to do with correlation energy. Obviously this scheme will not work for some elements that don't make diatomics or small simple molecules. There is also the point that this only seems to make sense for closed shell systems. It seems to me I saw some references on deriving VDW parameters on the AMBER WWW site. You might want to look there. I picked up some F parameters there. Dr. Ross Underhill Royal Military College of Canada Kingston, Ontario (613) 541-6000 X6175 Return-Path: mizan@engin.umich.edu A possible reference for Nonbonding interactions from ab initio calculations may be: Dinur, U. and A.T. Hagler, J. Am. Chem. Soc., 111, 5149-5151, 1989. Hope this helps. Tahmid Mizan University of Michigan Return-Path: d-white1@assistant.beckman.uiuc.edu Thomas Please either summarize this for the net or send me a copy of the replies. I am really intereted in this myself. Sincerely David White **************************************************************************** * * * * David White * Man is the best computer we can put * * Postdoctoral Research Associate * aboard a spacecraft -- and the only * * Beckman Institute * one that can be mass produced with * * (217) 244-1733 * unskilled labour * * (217) 244-8371 (fax) * Werner von Braun * * * * ****************************************************************************