From chemistry-request@ccl.net Thu Mar 5 06:51:26 1992 Date: Thu, 5 Mar 92 12:00:25 +0100 From: martin@biokth.sunet.SE (Martin Norin, Dept. Biochem., Royal Inst. Subject: MOPAC ESP charges-problems. To: "chemistry@ccl.net"@kth.sunet.SE Status: RO Dear Netters, I have a good experience in calculating atomic charges using the Electro- statical Potential fitting (ESP). I've been using the MOPAC 6.0 ESP program to calculate the point charges and then used them to assign organic molecules for AMBER MM/MD calculations. So far everything has been working successfully (the MM/MD calculations have reproduced experimental data). Now I have run into a problem: Obviously some times the ESP fitting breaks down or fail to converge to reasonable charges. I have calculated ESP charges of six different conformations charged molecule (-1). The different conformations were generated by a MD run and the minimized using MM. Three of these conformations yield charges that are almost the same but the remaining three conformations differs severely from each other and also gives unreasonable magnitudes of the charges. Like +4 and -9 for the atoms in a C=O group. What also can bee seen from the calculations are that the RMS DEVIATION of the electrostatic potential from the ESP charges versus the QM one is really large for these "failed" calculations. I have not seen this problem be mentioned in any article about any ESP programs (MOPAC ESP ot others). Does anybody have an idea of the reason for this problem ????? Could it be that a molecule in a packed conformation some atoms are "hidden" under the ESP surfaces by other exposed atoms and then the algorithm runs into troubles when calculating these hidden atoms charges or is it just that the algorithm fails to converge sometimes ?? or is it something else ???? I'll summarize the replies to the list !!!! Greetings /martin ************************************************************************ Martin Norin tel: +46-8-790 7512 Dept. Biochem fax: +46-8-723 1890 KTH e-mail: martin@physchem.kth.se 100 44 Stockholm Sweden ************************************************************************ DISCLAIMER: There is a theory that says that if anyone ever understands the laws of the Universe and why it exists it will immediately be replaced by something even more incomprehensible. Another theory says that this have already happened. /Freely after Douglas Adams. From chemistry-request@ccl.net Thu Mar 5 18:00:13 1992 Date: Thu, 5 Mar 1992 15:39 EST From: "DOUGLAS A. SMITH" Subject: Midwest Theoretical Chemistry Conference To: chemistry@ccl.net Status: RO Thanks to those of you who responded. No one knew the details, but I was told that Professor Kathy Hunt at Michigan State University was organizing the meeting. Prof. Hunt told me that the meeting is from June 4-6 at MSU, and that notices will be sent out soon. You can reach her at: Katharine C. Hunt Department of Chemistry Michigan State University East Lansing, MI 48824 (517) 355-9715 email: klch@enterprise.cem.msu.edu Doug Smith From chemistry-request@ccl.net Thu Mar 5 19:40:16 1992 Date: Thu, 5 Mar 1992 15:12:31 -0500 From: zheng@retina.chem.psu.EDU (Ya-Jun Zheng) To: jkl@MPS.OHIO-STATE.EDU Status: RO Could someone please give me Profeesor Karl Jug's e-mail address? Also, I would appreciate more information about SINDO1 program which has been recently parametrized for some transistion metals. Yajun Zheng From chemistry-request@ccl.net Thu Mar 5 19:54:08 1992 Date: Thu, 5 Mar 92 18:29:25 -0500 From: jle@world.std.COM (Joe M Leonard) Subject: Inquiry for cycle-burners To: chemistry@ccl.net Status: RO This is sort of a followup to jkl's posting regarding "what's next..." I'm interested in learning what folks burn SCADS of computer time doing. I know they do ab initio QM, as well as large-scale MD simulations, but is there anything else that's not getting the press? I'd really appreciate answers from folks managing supercomputer resources, or with large mini- super's or big superscalar workstation clusters... Reply to the net, or to me directly if bandwidth is a concern... Thanx in advance, Joe Leonard jle@world.std.com