From gregory@wucmd.wustl.edu Tue Nov 7 16:47:05 1995 Received: from wugate.wustl.edu for gregory@wucmd.wustl.edu by www.ccl.net (8.6.10/950822.1) id QAA20647; Tue, 7 Nov 1995 16:36:53 -0500 Received: from wucmd by wugate.wustl.edu (8.6.12/8.6.11) with SMTP id PAA28318; Tue, 7 Nov 1995 15:36:49 -0600 Received: by wucmd (931110.SGI/911001.SGI) for @wugate.wustl.edu:chemistry@www.ccl.net id AA02353; Tue, 7 Nov 95 15:22:42 -0600 Date: Tue, 7 Nov 1995 15:08:03 -0600 (CST) From: Gregory Nikiforovich Subject: Re: CCL:Global minimum (philosophical) problems... To: "Victor M. Rosas Garcia" Cc: chemistry@www.ccl.net In-Reply-To: <9511070941.ZM4954@irisdav.chem.vt.edu> Message-Id: Mime-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII On Tue, 7 Nov 1995, Victor M. Rosas Garcia wrote: > For the global minimum, we could easily prove or disprove: > "This particular conformer is higher in energy than the one we call 'global > minimum'." > By the same token, for a distribution: > "This particular conformer has an energy higher than our cutoff limit of > interest, (so we don't have to include it in the distribution)." > Since I like philosophical problems, let me comment. As far as we are interested in conformers (like in conformational search problem), energy is just a target function, and energy minimization is a way to find a conformer, i.e., a particular 3D arrangement of atoms/functional groups. If you look at the problem from this side, you would notice that several very similar 3D arrangements may possess different energies. On the other hand, some very different 3D arrangements can possess almost identical energies (e.g., enantiomers). So the true task of conformational search is not to find all conformers within a given cutoff; it is to find all different 3D arrangements within a given energy cutoff. This task is much more realistic, since the possibility of missing a really different 3D arrangement during any search is less than to miss a minimum close to "the global" one in energy. However, it is not philosophy any more... Best wishes. Gregory V. Nikiforovich Phone (314) 935-4677 Research Professor Fax (314) 935-4979 Center for Molecular Design E-mail address: Washington University gregory@wucmd.wustl.edu Lopata Hall, Box 1099 St.Louis, MO 63130