From ipcakc@vigyan.iisc.ernet.in Sun Sep 3 02:27:34 1995 Received: from sangam.ncst.ernet.in for ipcakc@vigyan.iisc.ernet.in by www.ccl.net (8.6.10/950822.1) id CAA25998; Sun, 3 Sep 1995 02:26:42 -0400 From: Received: from iisc.ernet.in (iisc.iisc.ernet.in [144.16.64.3]) by sangam.ncst.ernet.in (8.6.12/8.6.6) with SMTP id LAA14166 for ; Sun, 3 Sep 1995 11:57:08 +0530 Received: from vigyan.UUCP by iisc.ernet.in (ERNET-IISc/SMI-4.1) id AA05870; Sun, 3 Sep 95 12:00:45+0530 Received: by vigyan.iisc.ernet.in (smail2.3) id AA04648; 3 Sep 95 11:59:22 EST (Sun) To: CHEMISTRY@www.ccl.net Subject: 3-21G parameters for Bromine Date: 3 Sep 95 11:59:22 EST (Sun) Message-Id: <9509031159.AA04648@vigyan.iisc.ernet.in> Could anyone give me the 3-21G basis parameters for Bromine ? Thanks in advance. Sridhar ipcakc@vigyan.iisc.ernet.in From markz@msi.com Sun Sep 3 15:42:45 1995 Received: from msi.com for markz@msi.com by www.ccl.net (8.6.10/950822.1) id PAA29408; Sun, 3 Sep 1995 15:27:53 -0400 Received: from gomez (gomez.msi.com) by msi.com (4.1/SMI-4.1) id AA26365; Sun, 3 Sep 95 15:23:09 EDT Received: by gomez (920330.SGI/911001.SGI) for CHEMISTRY@www.ccl.net id AA05930; Sun, 3 Sep 95 15:27:04 -0400 Date: Sun, 3 Sep 1995 15:27:03 -0400 (EDT) From: "Mark A. Zottola" Subject: Conformational Analysis Results To: CHEMISTRY@www.ccl.net Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Netters: A while back I had requested references/pointers to schemes which would provide complete descriptions of conformational space for any given molecule. I did receive several pointers. Many thanks to those that responded. Original Post: Is there a gold standard for exhaustively searching conformational space for discrete conformers? I realize that there is systematic search (but this fails for large and floppy molecules). I can imagine using distance geometry as a source for exhausting conformational space as well. Is there a concensus on a method? I would prefer public domain or QCPE-available code as opposed to "professional" efforts. If there is sufficient interest, I will summarize to the list. Thanks! Responses: Mark, There is very little done in the field of completeness of conformational searches. However, there are some ideas out there: Smellie J Chem. Inf. Comput. Sci. 1995, 35, 285-294 Perez, J. Phys. Chem. 98:2318-2324 (1994) There are many methods you can use to explore the conformational space of a molecule. All of them, and to some extent systematic nested rotations can not ensure that your search is complete. Now if what you want is a program that will extensively search the space there are many good papers, and most of them use either molecular dynamics simulations or monte carlo, combined with some minimization step. Some of the ideas on the field : Wilson, J. Comp Chem 12: 342 (1991) Li, PNAS 84: 6611 (1987) Saunders, JACS 112:1419 (1990) You can also look into the use of Genetic Algorithms, etc. I recommend that you look into the Vol 3 of Reviews in Computational Chemistry,(Lipkowitz & Boyd). So the short answer is there is nothing that ensures that you did a complete search of the conformational space. There are some interesting ideas on how to do it. But regardless of which approach you decide to take, you will need to use extreme good judgement. A few more references for you to look over are: 6:175 (1992). There is plenty on how to get to a low energy conformer, there is very little on how to carry out an extensive and exhaustive search for minima. Good luck. Hugo O. Villar ******************************************************************************* For anything that involves a non-aromatic ring, I prefer distance geometry followed by optimization in an appropriate force-field or QM optimizer. This finds local minima. Any comparisons I have run shows we find more minima than other methods or that we at least find all that they do. Yvonne Martin Abbott Laboratories yvonne.martin@abbott.com ******************************************************************************* >From lipkowitz@chem.iupui.edu A great overview of conformational search strategies for medium sized molecules has been written by Andy Leach. It's volume 2 of Reviews in Computational Chemistry, VCH Publishers, 1991. *******************************************************************************