From chemistry-request@ccl.net Tue Jan 28 00:53:26 1992 Date: Mon, 27 Jan 1992 23:23 EST From: "DOUGLAS A. SMITH" Subject: Angelo Rossi To: chemistry@ccl.net Status: RO Angelo can be reached at rossi@watson.ibm.com. His phone number is 914-945-3834. Again, thanks to all who responded, and apologies to Angelo if he gets a ton of mail from this posting. Doug Smith From chemistry-request@ccl.net Tue Jan 28 03:36:35 1992 Date: Tue, 28 Jan 92 09:17 MET From: LOES KROON-BATENBURG Subject: Re:Generalized Karplus Calculations To: chemistry@ccl.net Status: RO There is a program " 3JHH2 " availabe from QCPE (nr. 591).It is written by K. Imai and E. Osawa and contains an extended form of the Karplus equation. Loes Kroon-Batenburg University of Utrecht bate@hutruu54.bitnet From chemistry-request@ccl.net Tue Jan 28 19:19:56 1992 Date: Tue, 28 Jan 92 18:37:01 -0500 From: bbesler@ouchem.chem.oakland.edu (Brent H. Besler) To: chemistry@ccl.net Subject: downloads available by anoymous FTP Status: R On ouchem.chem.oakland.edu the following are now available for download via anonymous ftp. CHELPG from Curt Brenneman Mopac 6.0 in both the Vax and DEC 3100 Unix(should work on any Unix system) version The Fortran versions of the microfiche programs from the McAllen & Tildesly book "Computer Simulation of Liquids" The IP address is 141.210.108.5 and all of the files are in pub or its subdirectories. From chemistry-request@ccl.net Tue Jan 28 20:47:35 1992 Date: Tue, 28 Jan 1992 19:25 CST From: Andy Holder Subject: SADDLE in MOPAC/AMPAC To: CHEMISTRY@ccl.net Status: R Hi Guys and Guyettes! A while back someone posted a messgae on using the SADDLE method to locate a transition state with one of the Dewar semiempirical pro- grams (MOPAC or AMPAC). My experience is that this is not as reliable as some other techniques. AMPAC has implemented the excellent CHAIN algorithm, installed by Daniel Liotard. This requires input of a guess transition state, and left and right minima. It has performed very well in locating reasonable TS's. SADDLE has some problems that almost require one to specify everything in Cartesian coordinates for it to function properly (if that will do the trick). I usually only resort to these automated procedures after the "shotgun" method has failed. When beginning, I make an approximate guess at the trans- ition state and use a gradient minimization routine (POWELL, NLLSQ, or LTRD). POWELL is generally the fastest. After a POWELL computation, one MUST MUST MUST calculate the force constant matrix. The output file contains an "estimate" of the number of imaginary frequencies that is generally wrong. (In fact, I have eliminated this part of the printout to avoid confusion to other users in my version.) LTRD is a very stable approach as it computes a full second deriv- ative matrix on each step. It's frequency calculations are reliable. To sum up: 1. estimate TS geometry (Hammond's postulate is useful here) 2. gradient minimize with POWELL, compute force constants 3. if POWELL fails, try LTRD gradient minimzation/force const. 4. if this fails use CHAIN to locate approximate TS and go back to step 2 5. if this fails, find an easier reaction! Notes: Multiple bond breaking/forming reactions will be hard. Grid searches along tow or more coordinates will be needed to get a good starting point for refinement. Even if you have a CRAY-ZMP59000, do the calculation with a semiempirical method before you waste time searching the pot- ential surface with a big, hairy ab initio method. Bye now. Hope the sermon helps out some folks. Andy Holder =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= DR. ANDREW HOLDER Assistant Professor of Computational/Organic Chemistry 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 =-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= From chemistry-request@ccl.net Tue Jan 28 22:18:57 1992 Date: Tue, 28 Jan 92 21:02 CDT From: CUNDARIT%MEMSTVX1.BITNET@OHSTVMA.ACS.OHIO-STATE.EDU To: chemistry@ccl.net Status: R Fellow Netters, Lately, a few letters have appeared on the network dealing with transition metal calculations. Although not as popular among the general computational crowd as organic or biomolecules, this seems like a good opportunity to try and get some discussion regarding these 30 elements. It is well known that transition metal complexes can be a bit tricky to converge, especially those in the first series where the bonding is less covalent. The best, but by no means foolproof, way to tackle this is the old- fashioned way: sit down with paper and pencil, think about the chemistry, draw a Lewis structure, localize intermediate MOs and plot them to make sure no "impostors" are occupied. If so, reorder them with the appropriate options in your favorite program. One "trick" for first row metals (if you use effective core potentials and do not have to worry about different size cores) is to run a "quick and dirty" on the heavier analogue in the same group. For example, if TiCl4 is a problem, try ZrCl4 or HfCl4 first, and if successful, plug these in as a starting guess for TiCl4. Another problem in our experience is that when DIIS is used before the MOs have a chance to "calm down" (usually 10-15 SCF cycles with damping and extrapolation), oscillation often results. Again, this is a bigger problem for the first row metals. The solution we have found is to have one run though with DIIS turned off and damping and extrapolation turned on, read these MOs in as an initial guess for the second attempt, with DIIS turned on. Although somewhat biased (having worked with the North Dakota State GAMESS bunch), my experience has been that Gaussian is more prone to convergence problems for transition metal complexes than GAMESS. Recently, new initial guess routines have been written for GAMESS which in our experience has virtually eliminated convergence problems even for notorious cases: first row metal complexes, coordinatively unsaturated complexes, high spin molecules. Sorry, if this sounds like an ad, but one "trick" would be to get a copy of GAMESS, hope for convergence and then read these MOs into your other favorite program as an initial guess. If anybody would like to comment on other tricks, progams or methods such as semiempirical or density functional (particularly the latter) that they have found successful in dealing with transition metals or even the lanthanides, I'd be interested in hearing in them. Sincerely, Thomas R. Cundari, Asst. Prof. Dept. of Chemistry Memphis State University Memphis, TN 38152 phone: (901)678-2629 FAX: MSU-FAXX e-mail: CUNDARIT@MEMSTVX1.MEMST.EDU