From rgab@purisima.molres.org Thu Apr 28 03:32:08 1994 Received: from purisima.molres.org for rgab@purisima.molres.org by www.ccl.net (8.6.4/930601.1506) id CAA21266; Thu, 28 Apr 1994 02:47:18 -0400 Message-Id: <199404280647.CAA21266@www.ccl.net> Received: by purisima.molres.org (1.37.109.4/16.2) id AA06350; Wed, 27 Apr 94 23:27:47 -0700 Date: Wed, 27 Apr 94 23:27:47 -0700 From: "R.G.A. Bone" To: chemistry@ccl.net Subject: Symmetry: Definitive References In view of the current comments on the philosophy of the use of symmetry in the computation of molecular potential energy surfaces, I thought it would be useful to put out a compendium of 'primary' references in this field. I revisited my (1992) PhD thesis and culled the following. It is worth restating, though, that there is no theorem which allows you claim that a minimum-energy structure (in fact, any stationary point) must have any point group symmetry at all, in the absence of other information, e.g., a force law. (The converse is open to serious discussion, nevertheless: - does a structure of given symmetry have to be a stationary point?) Symmetry can be used somewhat heuristically, however, with caution. And, as has also, already been stated, once one has located a stationary point (confirmed by checking all gradient components), the only sure way of testing whether or not it is a local minimum, is to calculate the Hessian. A general discussion of all basic features of PESs can be found in; ------------------ P.G.Mezey, Studies in Physical and Theoretical Chemistry, 53, "Potential Energy Hypersurfaces", Elsevier, (1987). Symmetry at Stationary Points ----------------------------- If one is looking for a 'proof' that the energy must be stationary w.r.t. all non-totally symmetric distortions (i.e., the oft-desired result that "symmetric structures are (frequently) stationary points") then there are two papers which address the issue (for a non-degenerate electronic state): D. J. Wales, J. Am. Chem. Soc., 112, 7908, (1990) - a paper which considers the balance of forces on the atoms at various points in a given structure. H. Metiu, J. Ross, R. Silbey and T. F. George, J. Chem. Phys.,61, 3200, (1974) This paper observes that the discussion is linked closely with the notion of expanding the local potential surface in normal coordinates (and their derivatives, etc.). [Because, of course, normal coordinates are guaranteed to transform as irreducible representations of the point group.] This, in turn, leads on to discussions of reaction paths, etc. and an understanding of how the gradient vector transforms under symmetry operations, a subject which has been addressed by many authors. Symmetry of the gradient. ------------------------- The first of these papers contains a straightforward and rigorous formal proof. J. W. McIver, Jr. and A. Komornicki, Chem. Phys. Lett., 10, 303, (1971) The papers by Pearson describe a perturbation-theory approach. R. G. Pearson, J. Am. Chem. Soc., 91, 1252, (1969) R. G. Pearson, J. Am. Chem. Soc., 91, 4947, (1969) R. G. Pearson, Theor. Chim. Acta., 16, 107, (1970) R. G. Pearson, J. Chem. Phys., 52, 2167, (1970) R. G. Pearson, Pure Appl. Chem., 27, 45, (1971) R. G. Pearson, Acc. Chem. Res., 4, 152, (1971) R. G. Pearson, Symmetry Rules for Chemical Reactions, Wiley Interscience, (1976) Rodger and Schipper have a formalism based upon normal-mode expansions. A. Rodger and P. E. Schipper, Chem. Phys., 107, 329, (1986) A *landmark* paper by Pechukas describes the properties of steepest-descent paths and leads to cornerstone statements of transition state symmetries. P. Pechukas, J. Chem. Phys., 64, 1516, (1976) Transition State Symmetry Rules ------------------------------- The believed limitations on the symmetries of transition states have lead to many analyses, beginning with Stanton and McIver: J. W. McIver, Jr. and R. E. Stanton, J. Am. Chem. Soc., 94, 8618, (1972) R. E. Stanton and J. W. McIver, Jr., J. Am. Chem. Soc., 97, 3632, (1975) J. W. McIver, Jr., Acc. Chem. Res., 7, 72, (1974) A. Rodger and P. E. Schipper, Chem. Phys., 107, 329, (1986) A. Rodger and P. E. Schipper, Inorg. Chem., 27, 458, (1988) A. Rodger and P. E. Schipper, J. Phys. Chem., 91, 189, (1987) R. G. A. Bone, Chem. Phys. Lett., 193, 557, (1992) Exceptions and Pitfalls ----------------------- The application of symmetry and many assumptions about the form of a PES can lead to problems if unusual features are present. The oft-cited example is that of a (putative) monkey-saddle (3rd order 'degenerate' critical point), but except where symmetry itself may impose severe restrictions on the form of the potential function, it is safe to assume that there will always be minor perturbations which lift the degeneracy. Near 4th-order critical points can arise on exceptionally flat surfaces and when symmetry demands that 3rd order terms in the potential must vanish. Far more frequent are bifur- cations. Strictly a "bifurcation" is a feature of a path. Valtazanos and Ruedenberg demonstrated their association with "valley-ridge inflection points" on a PES: P. Valtazanos and K. Ruedenberg, Theor. Chim. Acta., 69, 281, (1986) Bifurcations are legion. For description of one on a very simple and surpris- ing surface, see: R. G. A. Bone, Chem. Phys., 178, 255, (1993). Other more exotic examples, include: J. F. Stanton, J. Gauss, R. J. Bartlett, T. Helgaker, P. Jorgensen, H. J. Aa. Jensen and P. R. Taylor, J. Chem. Phys., 97, 1211, (1992). T. Taketsugu and T. Hirano, J. Chem. Phys., 99, 9806, (1993) The main significance of bifurcations in the context oif symmetry is that they are points at which, symmetry may be 'broken'. For a qualitative discussion of the plethora of forms of PES and the influence of point group symmetry, see: R. G. A. Bone, T. W. Rowlands, N. C. Handy and A. J. Stone, Molec. Phys., 72, 33, (1991) And, a paper which describes concepts useful for characterisation the local symmetry of potential energy surfaces in Jahn-Teller systems. A. Ceulemans, D. Beyens and L. G. Vanquickenbourne, J. Am. Chem. Soc., 106, 5824, (1984) Symmetry-breaking in Open-Shell Systems --------------------------------------- This subject has a long history, so I will be selective here: General considerations/review: E. R. Davidson, J. Phys. Chem., 87, 4783, (1983) UHF calculations: L. Farnell, J. A. Pople and L. Radom, J. Phys. Chem., 87, 79, (1983) D. B. Cook, Int. J. Quant. Chem., 43, 197, (1992) D. B. Cook, in "The Self-Consistent Field Approximation", Ed. R. Carbo D. B. Cook, J. Chem. Soc. Far. Trans. 2, 82, 187, (1986) P. O. Lowdin, Rev. Mod. Phys., 35, 496, (1963)( W. D. Allen and H. F. Schaefer, III, Chem. Phys., 133, 11, (1989) Calculations with MC-SCF/CAS-SCF P. Pulay and T. P. Hamilton, J. Chem. Phys., 88, 4926, (1988) J. M. Bofill and P. Pulay, J. Chem. Phys., 90, 3637, (1989) Calculations with a Coupled-Cluster Wavefunction J. D. Watts and R. J. Bartlett, J. Chem. Phys., 95, (1991) Final Comments: There is no definitive answer to the question of what role symmetry should play in a given molecular problem. There will always be a compromise between (computational) resources available and thoroughness of analysis. Sometimes it makes sense to start in high symmetry, sometimes not. Sometimes it is only possible to use symmetry - because of the difference it makes to the size of the calculation. In calculating a reaction path, it's probably a good idea to use as little symmetry as possible. When optimizing a geometry, symmetry will help you get to a stationary point (probably) but only a frequency calculation can tell you what it is. When searching for saddle-points, the theorems tell you that you'll only increase in symmetry (at the T.S.) if you're finding a T.S. for a 'degenerate' rearrangement. Otherwise, your transition state cannot be searched for by minimizing in a symmetry-constraint. This means that the majority of T.S.'s don't have any useful distinguishing symmetries. Sad, but true. Despite the zeal with which chemists have pursued those symmetric 'beauties', the Fullerenes, Nature more often displays low-symmetry than high-symmetry, but a bit of thought shows that two low-symmetry structures are often related to one another by a symmetry operation in a higher-symmetry 'midpoint' so symmetry of the PES is always conserved. Richard Bone ================================================================================ R. G. A. Bone. Molecular Research Institute, 845 Page Mill Road, Palo Alto, CA 94304-1011, U.S.A. Tel. +1 (415) 424 9924 x110 FAX +1 (415) 424 9501 E-mail rgab@purisima.molres.org From javito@netcom.com Thu Apr 28 04:32:11 1994 Received: from netcom.com for javito@netcom.com by www.ccl.net (8.6.4/930601.1506) id DAA21610; Thu, 28 Apr 1994 03:58:01 -0400 Received: by netcom.com (8.6.8.1/SMI-4.1/Netcom) id AAA20501; Thu, 28 Apr 1994 00:59:19 -0700 From: javito@netcom.com (James Vito) Message-Id: <199404280759.AAA20501@netcom.com> Subject: postscript viewer for PC? To: chemistry@ccl.net Date: Thu, 28 Apr 1994 00:59:18 -0700 (PDT) X-Mailer: ELM [version 2.4 PL23] MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Content-Length: 271 I have a doc file that is in postscript format. I don't have an application to view the file properly. maybe I am missing something here. Any suggestions.... I do have ms-windows 3.1 maybe there is some program that I can ftp get? Thanks. Jim Vito javito@netcom.com From toukie@zui.unizh.ch Thu Apr 28 05:32:09 1994 Received: from rzusuntk.unizh.ch for toukie@zui.unizh.ch by www.ccl.net (8.6.4/930601.1506) id FAA21882; Thu, 28 Apr 1994 05:19:10 -0400 Received: from rzurs6.unizh.ch by rzusuntk.unizh.ch (4.1/SMI-4.1.9) id AA02188; Thu, 28 Apr 94 11:18:56 +0200 Received: by rzurs6.unizh.ch (AIX 3.2/UCB 5.64/4.03) id AA17837; Thu, 28 Apr 1994 11:18:45 +0200 From: toukie@zui.unizh.ch (Hr Dr. S. Shapiro) Message-Id: <9404280918.AA17837@rzurs6.unizh.ch> Subject: Software for prediction of pKa values To: chemistry@ccl.net Date: Thu, 28 Apr 1994 11:18:44 +0100 (MEST) Cc: bz@cdk-cgx.hu X-Mailer: ELM [version 2.4 PL13] Content-Type: text Content-Length: 754 Dear Dr. Welsh (and prospective others); An excellent programme for predicting pKa values for organic acids and bases is "pKalc", manufactured by CompuDrug Chemistry, Ltd. Furst Sandor utca 5 H-1136 Budapest The Marketing Director for CompuDrug Chemistry, Ltd. is Dr. Zoltan Bencz; his e-mail address is: bz@cdk-cgx.hu CompuDrug's FAX number is (0036 1) 132'25'74 CompuDrug has a marketing office in the United States. For details, please con- tact CompuDrug directly. Sincerely, S. Shapiro Abt. orale Mikrobiol. allg. Immunol. Zahnaerztl. Inst. der Univ. ZH Plattenstr. 11 Postfach CH-8028 Zuerich Internet: toukie@zui.unizh.ch From wolpert@neon.chem.utk.edu Thu Apr 28 08:32:13 1994 Received: from neon.chem.utk.edu for wolpert@neon.chem.utk.edu by www.ccl.net (8.6.4/930601.1506) id HAA22643; Thu, 28 Apr 1994 07:52:29 -0400 Received: by neon.chem.utk.edu (4.0/1.34) id AA17259; Thu, 28 Apr 94 07:52:50 EDT Date: Thu, 28 Apr 94 07:52:50 EDT From: wolpert@neon.chem.utk.edu (Edward Wolpert) Message-Id: <9404281152.AA17259@neon.chem.utk.edu> To: rgab@purisima.molres.org Cc: chemistry@ccl.net In-Reply-To: <199404271844.OAA15112@www.ccl.net> (rgab@purisima.molres.org) Subject: CCL:USENET News Group ... YES! Netters- Actually, UseNet news and the mail-list can be intergrated, so people who do not have usenet news can still get all the info passed into either list. Many folks have 'digests' where an article is submitted, and will be posted via news and listserver. Some cases, such articles are moderated, and in other's they are not. By doing this sort of scheme, you can reach more people. Of course, this is a double edge sword, since UseNet news has been in the past abused. (Some mailings have been abused as well, but not as much as UseNet, since UseNet is more well known than individual mailing lists.) At this least, perhaps ccl.net should post an 'ad' once a month, for this mailing list, so that everyone who reads that group will know about this list. Virtually, Edward Wolpert --------------------------- -------------------- wolpert@utk.edu | System Administrator | "No, sorry, there's wolpert@osti.rmt.utk.edu | Systems Programmer | nothing to be pa153568@utkvm1.utk.edu | Graduate Chemistry Student | done about it." --------------------------- -------------------- I'm sorry, but Godot isn't here today. Perhaps if you came back tomorrow... home page From SERGEI@ps1515.chemie.uni-marburg.de Thu Apr 28 08:48:31 1994 Received: from Mailer.Uni-Marburg.DE for SERGEI@ps1515.chemie.uni-marburg.de by www.ccl.net (8.6.4/930601.1506) id HAA22594; Thu, 28 Apr 1994 07:42:25 -0400 Received: from ps1515.Chemie.Uni-Marburg.DE by Mailer.Uni-Marburg.DE (AIX 3.2/UCB 5.64/19.11.93) id AA50273; Thu, 28 Apr 1994 13:44:06 +0200 Received: from NWS_CHEMIE/MAILQ by ps1515.chemie.uni-marburg.de (Mercury 1.11); Thu, 28 Apr 94 13:44:24 GMT+2 Received: from MAILQ by NWS_CHEMIE (Mercury 1.11); Thu, 28 Apr 94 13:43:54 GMT+2 To: CHEMISTRY@ccl.net From: "Sergei Vyboishchikov" Date: 28 Apr 94 13:43:46 MDT Subject: Symmetry again Priority: normal X-Mailer: Pegasus Mail v2.3 (R5). Message-Id: <1F401EB035D@ps1515.chemie.uni-marburg.de> Dear Netters, I have some comments concerning the discussion about symmetry. R.G.A.Bone wrote: >The gradient of the energy w.r.t. nuclear displacements should transform >as the totally symmetric 'irrep' in whatever point group you happen to be >in. For 'closed-shell' systems (no electronic degeneracies) this means in >practice that 'symmetric' structures are usually stationary points. E.Lewars wrote: >Does anybody know of a formal theorem that says non-C1 structures are >always stationary points? Yes, I do. There is the rigorous theorem that states that any symmetrical structure is a stationary point with respect to NOT totally symmetric nuc- lear displacements. I know some references to this statement but only in Russian textbooks (sorry). This is a purely geometrical statement and does not depend upon the symmetry of electronic state and whether or not the system has closed shells only. The molecules with Jahn-Teller effect are not exclusions. Their symmetric structures are also stationary points, but not minima. But the term "stationary point" is defined as a point where all partial derivatives (consequently, gradient) is equal to zero. It need not be a maximum or a minimum, but can be a saddle point. If one optimizes geometry within symmetry constraints, it guarantees that the found stricture is a minimum with respect to totally symmetric nuclear displacements and hence a stationary point with respect to all possible displacements. Note that one starts optimizing a structure from a symmetrical geometry, it is impossible to come to a structure with a lower symmetry, no matter this symmetry is imposed explicitly (using variables with the same names in Z-matrix) or simply actually present in the starting geometry. This is due to the fact that "the gradient of the energy w.r.t. nuclear displacements should transform" as R.Bone writes. (however, not "should transform" but "does transform"). The error messages such as GAUSSIAN's "change of point group or standard orientation" arises either from numerical errors in transforming Cartesian coordinates into internal or from "false" Z-matrix (in which some parameters are denoted by the same variables though they are not symmetrically equivalent). Sergei F.Vyboishchikov Universitaet Marburg, Germany E-Mail: sergei@ps1515.chemie.uni-marburg.de From jmiller@SANDCASTLE.COSC.BROCKU.CA Thu Apr 28 10:32:29 1994 Received: from nexus.BrockU.CA for jmiller@SANDCASTLE.COSC.BROCKU.CA by www.ccl.net (8.6.4/930601.1506) id JAA24145; Thu, 28 Apr 1994 09:38:17 -0400 Received: from sandcastle.cosc.BrockU.CA by nexus.BrockU.CA via SMTP (920110.SGI/911001.SGI.UNSUPPORTED.PROTOTYPE) for CHEMISTRY@ccl.net id AA13085; Thu, 28 Apr 94 09:38:45 -0400 Received: from applepie.chem.BrockU.CA by SANDCASTLE.COSC.BROCKU.CA via SMTP (920330.SGI/920502.SGI) for @NEXUS.BROCKU.CA:CHEMISTRY@ccl.net id AA03353; Thu, 28 Apr 94 09:38:24 -0400 Date: Thu, 28 Apr 94 09:38:24 -0400 Message-Id: <9404281338.AA03353@SANDCASTLE.COSC.BROCKU.CA> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" To: CHEMISTRY@ccl.net From: jmiller@SANDCASTLE.COSC.BROCKU.CA (Jack Martin Miller) Subject: Molecular Modeling Programs Would anyone care to comment on the relative merits and/or their experiences with of BioGraph, Cerius2 and Biosym molecular modeling programs bot in general and for applications involving metals including octahedral configurations and for solvation studies. Jack Martin Miller Professor of Chemistry Adjunct Professor of Computer Science Brock University, St. Catharines, Ontario, Canada, L2S 3A1. Phone (905) 688 5550, ext 3402 FAX (905) 682 9020 e-mail jmiller@sandcastle.cosc.brocku.ca From bewilson@emn.com Thu Apr 28 10:49:36 1994 Received: from emngw1.emn.com for bewilson@emn.com by www.ccl.net (8.6.4/930601.1506) id KAA24562; Thu, 28 Apr 1994 10:08:38 -0400 Received: by emngw1.emn.com (AIX 3.2/UCB 5.64/4.03) id AA22962; Thu, 28 Apr 1994 10:07:20 -0400 Date: Thu, 28 Apr 1994 10:07:20 -0400 From: bewilson@emn.com (Wilson_Bruce) Message-Id: <9404281407.AA22962@emngw1.emn.com> To: chemistry@ccl.net Subject: Re: Polymer conformation calculations Jens Lehmann asks about calculating the preferred conformations of the monomers in a poly(aryletherketon) --- It has been our experience here that getting the correct relative rotational energies for aromatic ketones/carboxylic acids (e.g. terephthalic acid) is somewhat difficult. The energy barrier between conformers is very low and the energy differences are slight. Generating the parameters for a rotational isomeric state model is somewhat problematic then. You can use basically two approaches. One is to model pieces, using ab initio code (at least 3-21G*) to get the rotational energies for a RIS model (I've not been satisfied when I've tried doing this with AM1 or PM3). The second is a periodic cell type annealing experiment. The trick here is to get the cell to match the observed density of the polymer at the desired temperature. Several commercial packages have the tools to be able to do this (Biosym, Sybyl, ...). I can't help on which would be "best" though the Sybyl force field is qualitative, not quantitative, IMO, which may limit the applicability to this particular problem. Bruce Wilson (bewilson@emn.com) From shenkin@still3.chem.columbia.edu Thu Apr 28 11:32:16 1994 Received: from still3.chem.columbia.edu for shenkin@still3.chem.columbia.edu by www.ccl.net (8.6.4/930601.1506) id KAA25157; Thu, 28 Apr 1994 10:35:38 -0400 Received: by still3.chem.columbia.edu (931110.SGI/930416.SGI.AUTO) for chemistry@ccl.net id AA15619; Thu, 28 Apr 94 10:17:11 -0400 From: "Peter Shenkin" Message-Id: <9404281016.ZM15617@still3.chem.columbia.edu> Date: Thu, 28 Apr 1994 10:16:59 -0400 In-Reply-To: "R.G.A. Bone" "CCL:Symmetry: Definitive References" (Apr 27, 11:27pm) References: <199404280647.CAA21266@www.ccl.net> X-Mailer: Z-Mail (3.1.0 22feb94 MediaMail) To: "R.G.A. Bone" , chemistry@ccl.net Subject: Re: CCL:Symmetry: Definitive References Content-Type: text/plain; charset=us-ascii Mime-Version: 1.0 On Apr 27, 11:27pm, R.G.A. Bone wrote: > Subject: CCL:Symmetry: Definitive References > It is worth restating, though, that there is no theorem which > allows you claim that a minimum-energy structure (in fact, any > stationary point) must have any point group symmetry at all, in > the absence of other information, e.g., a force law. (The > converse is open to serious discussion, nevertheless: - does a > structure of given symmetry have to be a stationary point?) Excuse me; I'm not an expert on this sort of thing, so I may be missing something, but consider ethane in the staggered conformation. This conformation is an energetic minimum, and has point-group symmetry. If I simply stretch or compress the C-C bond, I do not change the point-group, but I am no longer at a minimum, nor at any other stationary point. Doesn't this demonstrate that symmetric structures need not be stationary points? -P. -- ********************** "So much for global warming...." ********************* Peter S. Shenkin, Box 768 Havemeyer Hall, Dept. of Chemistry, Columbia Univ., New York, NY 10027; shenkin@still3.chem.columbia.edu; (212) 854-5143 ***************************************************************************** From SATYAM@vms.cis.pitt.edu Thu Apr 28 12:32:16 1994 Received: from VM2.CIS.PITT.EDU for SATYAM@vms.cis.pitt.edu by www.ccl.net (8.6.4/930601.1506) id LAA26234; Thu, 28 Apr 1994 11:45:25 -0400 From: Received: from vms.cis.pitt.edu by vms.cis.pitt.edu (PMDF V4.2-14 #4065) id <01HBPH3HESPCDHSN5M@vms.cis.pitt.edu>; Thu, 28 Apr 1994 11:45:10 EST Date: Thu, 28 Apr 1994 11:45:10 -0500 (EST) Subject: Help with integration for some student.. To: chemistry@ccl.net Message-id: <01HBPH3HF2CIDHSN5M@vms.cis.pitt.edu> X-Envelope-to: chemistry@ccl.net X-VMS-To: IN%"chemistry@ccl.net" MIME-version: 1.0 Content-transfer-encoding: 7BIT Dear Netters Some student is looking for references/details to perform analytical integration of the type :: Sin(a * x1) * (1./(|x1 - x2| )) * Sin(b * x1) * dx1 over the limit xmin <= x1 <= xmax If enough interest I will summarize on behalf of the student Thanks Satyam From stephan.irle@itc.univie.ac.at Thu Apr 28 12:45:49 1994 Received: from itc.univie.ac.at for stephan.irle@itc.univie.ac.at by www.ccl.net (8.6.4/930601.1506) id LAA26383; Thu, 28 Apr 1994 11:52:48 -0400 Received: from retsina.itc.univie.ac.at. (retsina.itc.univie.ac.at) by itc.univie.ac.at (5.65c/ITC-Vie(tk)-1.1m) id AA14808; Thu, 28 Apr 1994 17:50:47 +0200 Received: by retsina.itc.univie.ac.at. (5.65c/ITC-Vie(tk)-1.1s) id AA16046; Thu, 28 Apr 1994 17:47:53 +0200 From: stephan.irle@itc.univie.ac.at (Stephan Irle) Message-Id: <199404281547.AA16046@retsina.itc.univie.ac.at.> Subject: CT-complexes of pi-systems To: chemistry@ccl.net (Post Articles to CCL) Date: Thu, 28 Apr 1994 17:47:52 +0100 (MESZ) Organization: Institute of Theoretical Chemistry, University of Vienna Phone: (+43/1) 40480-670, priv. 423499 Postal-Address: Waehringer Str. 17, A-1090 Wien, Austria Private-Address: Speckbachergasse 30/23, A-1160 Wien, Austria X-Mailer: ELM [version 2.4 PL20] Content-Type: text Content-Length: 957 Dear netters, we do SCF and MP2 calculations on li/na "doped" oligomers of polythiophene/ polyphenylene (n=1,...,4). Our aim is to examine the mechanism of the charge transfer and the geometry relaxation of the molecule. We would be very glad for any hint concerning other ab-inito calculations on this topic that exist in the literature. Please reply to the e-mail address given below. Thank you in advance! Stephan Irle and Hans Lischka -------------------------------------------------------------------------------- + Stephan Irle .&______~*@*~______&. m Stephan.Irle@itc.univie.ac.at "w/%%%%%%%%%%%%%%%%%%%\w" mmm*** Institute for Theoretical `Y""Y""Y"""""Y""Y""Y' mm***** Chemistry and Radiation p-p_|__|__|_____|__|__|_q-q mm**Y** Chemistry, University of _-[EEEEM==M==MM===MM==M==MEEEE]-_.|..|.... Vienna, Austria From chem4@dvc.edu Thu Apr 28 13:32:18 1994 Received: from viking.dvc.edu for chem4@dvc.edu by www.ccl.net (8.6.4/930601.1506) id MAA26863; Thu, 28 Apr 1994 12:36:01 -0400 Received: by viking.dvc.edu (Smail3.1.28.1 #1) id m0pwZ5W-000Rk6C; Thu, 28 Apr 94 09:37 PDT Date: Thu, 28 Apr 1994 09:37:21 -0700 (PDT) From: Chem Student 4 Subject: information To: chemistry@ccl.net Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII I am a student at a junior college in Pleasant Hill, Ca I would appreciate it if you could send the address for Torganal. Also, could you tell me how to get program File Transfer Protocal. Thank you From elewars@alchemy.chem.utoronto.ca Thu Apr 28 14:32:25 1994 Received: from alchemy.chem.utoronto.ca for elewars@alchemy.chem.utoronto.ca by www.ccl.net (8.6.4/930601.1506) id OAA28169; Thu, 28 Apr 1994 14:04:09 -0400 Received: from localhost (elewars@localhost) by alchemy.chem.utoronto.ca (8.6.4/8.6.4) id OAA15578 for chemistry@ccl.net; Thu, 28 Apr 1994 14:03:22 -0400 Date: Thu, 28 Apr 1994 14:03:22 -0400 From: "E. Lewars" Message-Id: <199404281803.OAA15578@alchemy.chem.utoronto.ca> To: chemistry@ccl.net Subject: symmetry again, re staggered ethene Peter Shenkin wites: "...consider ethane in the staggered conformation. This conf is an energetic minimum, and point-group symmetry. If I simply stretch or compress the C-C bond, I do not change the point group, but I am no longer at a minimum, nor at any other stationary point. Doesn't this demonstrate that symmetric structures need not be stationary points?" Yes, but wer're not really asking if a symmetric structure of *arbitrary* geometry is a stationary point, but rather if such a structure, optimized within the limits of its symmetry (keeping the Sch:/nfliess point group, e.g. C2v, Cs, etc) must go to a stationary point. === From moshe_o@VNET.IBM.COM Thu Apr 28 14:35:15 1994 Received: from VNET.IBM.COM for moshe_o@VNET.IBM.COM by www.ccl.net (8.6.4/930601.1506) id OAA28448; Thu, 28 Apr 1994 14:20:34 -0400 Message-Id: <199404281820.OAA28448@www.ccl.net> Received: from HAIFASC3 by VNET.IBM.COM (IBM VM SMTP V2R2) with BSMTP id 8990; Thu, 28 Apr 94 14:19:36 EDT Date: Thu, 28 Apr 94 20:51:50 IDT From: "Moshe Olshansky" To: chemistry@ccl.net Subject: Hartree-Fock on PC Dear netters! I want to thank all those who responded to my query. Below you will find some of the responses I got. Before doing that I would like to make 3 remarks: 1) some of you suggested to get Gaussian 92 for Windows. I contacted Gaussian Inc. and their response was that for the PC they have only the binary version and that currently they do not intend to release the source code (they certainly distribute source code for "bigger" machines - $20,000 commercial, $2,00 academic) 2) another suggestion was to use the source code found in Szabo and Ostlund's "Modern Quantum Chemistry". I will look into that option. However, if I remember correctly, they compute ERIs containing only s and p orbitals. Moreover, I do not think that they cared too much about their code's efficiency. 3) I will investigate more the other possibilities. Let me know if you are interested in what I find (or do you want me to summarize for the net?). Well, now the responses: ------------------------------------------------------------------------- ......................................................................... ------------------------------------------------------------------------- ========================================================================= Received: from gatekeeper.es.dupont.com by vnet.IBM.COM (IBM VM SMTP V2R2) with TCP; Tue, 26 Apr 94 11:00:36 EDT Received: by gatekeeper.es.dupont.com (5.65/ULTRIX-mjr-062991); id AA08083; Tue, 26 Apr 94 11:01:28 -0400 Received: by esds01.es.dupont.com; id AA03001; Tue, 26 Apr 94 10:58:22 -0400 From: fredvc@esvax.dnet.dupont.com Message-Id: <9404261458.AA03001@esds01.es.dupont.com> Received: from esvax.dnet; by esds01.dnet; Tue, 26 Apr 94 11:01:27 EDT Date: Tue, 26 Apr 94 11:01:27 EDT To: moshe_o@vnet.ibm.com Cc: fredvc@esvax.dnet.dupont.com Apparently-To: moshe_o@vnet.ibm.com Subject: RE: CCL:Hartree Fock on PC You should begin by contacting Michel Dupuis, who is the keeper of HONDO v8.x for IBM. His e-mail address is: michel@kgnvmt.vnet.ibm.com Good Hunting!! ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ FREDERIC A. VAN-CATLEDGE Scientific Computing Division || Office: (302) 695-1187 or 529-2076 Central Research & Development Dept. || The DuPont Company || FAX: (302) 695-9658 P. O. Box 80320 || Wilmington DE 19880-0320 || Internet: fredvc@esvax.dnet.dupont.com -------------------------------------------------------------------------------- Opinions expressed in this electronic message should ***> NOT <*** be taken to represent the official position(s) of the DuPont Company. *****> ANY OPINIONS EXPRESSED ARE THE PERSONAL VIEWS OF THE AUTHOR ONLY. <***** ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ ========================================================================= Received: from garfield.cs.mun.ca by vnet.IBM.COM (IBM VM SMTP V2R2) with TCP; Tue, 26 Apr 94 11:16:20 EDT Received: from riemann.math.mun.ca (cory@riemann.math.mun.ca [134.153.1.200]) by garfield.cs.mun.ca with SMTP id <408862>; Tue, 26 Apr 1994 12:48:15 -0230 Received: (cory@localhost) by riemann.math.mun.ca (8.6.8/8.6.4) id MAA09447 for moshe_o@vnet.ibm.com; Tue, 26 Apr 1994 12:40:14 -0230 Date: Tue, 26 Apr 1994 12:40:14 -0230 From: "Cory C. Pye" Message-Id: <199404261510.MAA09447@riemann.math.mun.ca> To: moshe_o@VNET.IBM.COM Subject: 4 center - 2-electron repulsion integrals Talk to my Ph. D. supervisor, Raymond A. Poirier. He has a code called MUNGAUSS which is written in FORTRAN and is 'object-oriented'. The code is a distant cousin of MONSTERGAUSS from the University of Toronto. I don't think that there is a PC version, so some twiddling may be necessary. Contact him at rpoirier@kean.ucs.mun.ca , and tell him that I sent you. :-) -Cory Pye ========================================================================= Received: from kalypso.iqm.unicamp.br by vnet.IBM.COM (IBM VM SMTP V2R2) with TCP; Tue, 26 Apr 94 13:05:58 EDT Received: (vazquez@localhost) by kalypso.iqm.unicamp.br (8.6.8/8.3) id OAA05153; Tue, 26 Apr 1994 14:09:39 -0300 From: Pedro A M Vazquez Message-Id: <199404261709.OAA05153@kalypso.iqm.unicamp.br> Subject: hf on pc To: moshe_o@vnet.ibm.com Date: Tue, 26 Apr 1994 14:09:33 -0300 (GMT-0300) X-Mailer: ELM [version 2.4 PL23] Content-Type: text Content-Length: 335 hello I'm running GAMESS on 486 machines both under os2 and a free unix (freebsd). Gamess while not PD is free and distributed in full source code. I think is what looking for, if you have a 486 or pentium based PC and like unix go freebsd, if you do prefer os2 go this way both are good for what you're looking for. Regards Pedro ========================================================================= Received: from danpost.uni-c.dk by vnet.IBM.COM (IBM VM SMTP V2R2) with TCP; Wed, 27 Apr 94 02:10:17 EDT Received: from localhost (ean@localhost) by danpost.uni-c.dk (8.6.4/8.6) id HAA05403 for moshe_o@vnet.ibm.com; Wed, 27 Apr 1994 07:25:12 +0200 Date: 27 Apr 94 7:25 +0200 From: Frank Jensen To: moshe_o@vnet.ibm.com Message-ID: <1121*frj@dou.dk> Subject: HF on PC I'm not sure what kind of OS you will be running on the PC, but in any you'll need a fortran and probably also a C compiler. You may try the Gamess-US package, that runs on a variety of UNIX boxes. It comes with source code etc., and is free of charge. Contact Mike Schmidt for info (mike@si.fi.ameslab.gov) Frank ========================================================================= Received: from AWIUNI11.EDVZ.UniVie.AC.AT by vnet.IBM.COM (IBM VM SMTP V2R2) with TCP; Wed, 27 Apr 94 02:39:33 EDT Received: from AWIUNI11.EDVZ.UNIVIE.AC.AT by AWIUNI11.EDVZ.UniVie.AC.AT (IBM VM SMTP V2R2) with BSMTP id 5968; Wed, 27 Apr 94 08:39:54 MEZ Received: from AWIUNI11.EDVZ.UNIVIE.AC.AT (NJE origin C7081DAA@AWIUNI11) by AWIUNI11.EDVZ.UNIVIE.AC.AT (LMail V1.2a/1.8a) with BSMTP id 7640; Wed, 27 Apr 1994 08:39:53 +0100 Date: Wed, 27 Apr 94 08:28:33 MEZ From: C7081DAA@AWIUNI11.EDVZ.UniVie.AC.AT Subject: Re: CCL:Hartree Fock on PC To: Moshe Olshansky In-Reply-To: Your message of Tue, 26 Apr 94 15:28:27 IDT Hi , Moshe ! I would suggest HONDO 8.something from Michael Dupuis. It is a very clearly written program , not too big in the SCF-part. Michael works at IBM. His mail is schin@yktvmz As far as I know, his program together with a few enhancements is available for ca. $300. The program has been running successfully on a PC. Michael Department of Chemistry, Organic Division University of Florida ========================================================================= Received: from peladon.rmit.EDU.AU by vnet.IBM.COM (IBM VM SMTP V2R2) with TCP; Thu, 28 Apr 94 00:13:55 EDT Received: from thal.xx.rmit.EDU.AU by peladon.rmit.EDU.AU with SMTP id AA26780 (5.65c/IDA-1.4.4 for ); Thu, 28 Apr 1994 14:14:27 +1000 Received: From RMITCC/WORKQUEUE2 by thal.xx.rmit.EDU.AU via Charon-4.0-VROOM with IPX id 100.940428140337.1696; 28 Apr 94 14:14:28 -1000 Message-Id: To: moshe_o@VNET.IBM.COM From: "Assoc.Prof. Robert Shanks" Date: 28 Apr 1994 14:04:02 EST-10 Subject: Re: CCL:Hartree Fock on PC Reply-To: ShanksRA@rmit.edu.au Priority: normal X-Mailer: Pegasus Mail/Mac v2.02 Dear Dr Olshansky, I recommend HyperChem, distibuted by Autodesk Inc. It has both HF and molecular mechanics. We have found it a very complete simulation program. It has many graphical representations for the molecules. Some calculations take a long time, but we do these over the weekend. We use an Intel 486 computer with MS-Windows. Yours sincerely, Robert Shanks Assoc. Prof. Robert A. Shanks Associate Professor of Polymer Science Department of Applied Chemistry Royal Melbourne Institute of Technology From fercu@cwgk.chem.cwru.edu Thu Apr 28 15:32:23 1994 Received: from cwgk.chem.cwru.edu for fercu@cwgk.chem.cwru.edu by www.ccl.net (8.6.4/930601.1506) id OAA28987; Thu, 28 Apr 1994 14:53:30 -0400 From: Received: by cwgk.chem.cwru.edu (MX V3.3 VAX) id 8470; Thu, 28 Apr 1994 14:54:52 EDT Date: Thu, 28 Apr 1994 14:54:50 EDT To: CHEMISTRY@ccl.net Message-ID: <0097DA2F.01A0B1E7.8470@cwgk.chem.cwru.edu> Subject: pKa program There is a QSAR-type program for predicting pKa's of organic acids, built on a database of some 2000 compounds. It is available through Discovery Software Inc. For pricing information, please contact Dr. Mario Dimayuga (Email address: mld8@po.cwru.edu). Dan Fercu Department of Chemistry Case Western Reserve University 10900 Euclid Ave. Cleveland, OH 44106 From rgab@purisima.molres.org Thu Apr 28 15:33:59 1994 Received: from purisima.molres.org for rgab@purisima.molres.org by www.ccl.net (8.6.4/930601.1506) id OAA29071; Thu, 28 Apr 1994 14:57:57 -0400 Message-Id: <199404281857.OAA29071@www.ccl.net> Received: by purisima.molres.org (1.37.109.4/16.2) id AA07439; Thu, 28 Apr 94 11:38:28 -0700 Date: Thu, 28 Apr 94 11:38:28 -0700 From: "R.G.A. Bone" To: chemistry@ccl.net Subject: Symmetry: reply to Peter Shenkin Ok, I'll make this my last statement on this subject: Peter Shenkin writes in reply to my latest... >> It is worth restating, though, that there is no theorem which >> allows you claim that a minimum-energy structure (in fact, any >> stationary point) must have any point group symmetry at all, in >> the absence of other information, e.g., a force law. (The >> converse is open to serious discussion, nevertheless: - does a >> structure of given symmetry have to be a stationary point?) > > Excuse me; I'm not an expert on this sort of thing, so I may > be missing something, but consider ethane in the staggered > conformation. This conformation is an energetic minimum, and > has point-group symmetry. If I simply stretch or compress the > C-C bond, I do not change the point-group, but I am no longer > at a minimum, nor at any other stationary point. > > Doesn't this demonstrate that symmetric structures need not > be stationary points? > > -P. > Yes, he is right, I was being a little sloppy; in my first posting on this subject, I amplified the same point ... > ... this means in practice > that 'symmetric' structures are usually stationary points.The only distortions > to which the energy gradient could be non-zero are totally symmetric. Thus one > should be cautious with, say, van der Waals clusters, in which a totally- > symmetric distortion which corresponds to dissociation might be favourable if > the high-symmetry structure contains repulsions. The distortion that Shenkin mentions is, of course, totally symmetric (A_1g in D3d point group). I guess I shouldn't have made the unqualified statement, assuming that people would remember a detail of an earlier posting. The remaining missing qualifier from the basic statement is that one assumes that one's "symmetric structure" has been energy-minimized. Perhaps one can remove potential confusion by stating that: if one has a structure of given symmetry, then one can probably find a stationary point by energy-minimization, constraining that symmetry. The energy has changed only w.r.t. totally-symmetric distortions of the initial structure. This is not the same as suggesting that symmetric structures are often stationary- points, which I accept is rather a bold statement, given that any structure can be subjected to an infinitesimal distortion. The main point of practicality is that the energy of a symmetric structure will be stationary w.r.t. non- totally-symmetric distortions; in most instances a 'guessed' structure of a given symmetry (particularly high symmetry) will be close to a stationary point (requiring small changes only in the totally symmetric degrees of freedom to minimize to it). And in that sense one may loosely state that symmetric structures commonly turn out to be stationary points. As we can all see - symmetry is a complicated subject and one which is difficult to write about. Apologies if I clouded the issue. Till the next 'virtual interaction' ... Richard Bone ================================================================================ R. G. A. Bone. Molecular Research Institute, 845 Page Mill Road, Palo Alto, CA 94304-1011, U.S.A. Tel. +1 (415) 424 9924 x110 FAX +1 (415) 424 9501 E-mail rgab@purisima.molres.org From boehm@bohr.cem.msu.edu Thu Apr 28 16:32:18 1994 Received: from msu.edu for boehm@bohr.cem.msu.edu by www.ccl.net (8.6.4/930601.1506) id PAA29978; Thu, 28 Apr 1994 15:47:50 -0400 Received: from bohr.cem.msu.edu by msu.edu (IBM VM SMTP V2R2) with TCP; Thu, 28 Apr 94 15:47:59 EDT Received: by bohr.cem.msu.edu (920330.SGI/911001.SGI) for @msu.edu:CHEMISTRY@ccl.net id AA25179; Thu, 28 Apr 94 15:46:49 -0400 Date: Thu, 28 Apr 94 15:46:49 -0400 From: boehm@bohr.cem.msu.edu (Randy Boehm) Message-Id: <9404281946.AA25179@bohr.cem.msu.edu> To: CHEMISTRY@ccl.net Subject: summer_workshop This is to announce a summer workshop: ELECTRONIC PROPERTIES OF SOLIDS USING CLUSTER METHODS Michigan State University, July 17-19 (1994) organizing committee: T. A. Kaplan & S. D. Mahanti (1,3) J. F. Harrison, (2,3) Department of Physics & Astronomy Department of Chemistry Center for Fundamental Materials Research goals are to understand: A) intrinsic limitations of cluster methods as applied to electronic properties of solids B) relative strengths of various implementations of these methods (SCF, CI, LDA, etc.) partial list of invited speakers: P. Bagus, IBM Almaden Res. Ctr. J. Callaway, Louisiana State Univ. T. P. Das, SUNY, Albany D. E. Ellis, Northwestern Univ. M. A. Garcia-Bach, Univ. de Barcelona R. L. Martin, Los Alamos W. C. Nieuwpoort, Univ. of Groningen J. Vail, Univ. of Manitoba J. L. Whitten, North Carolina State Univ. R. Zeller, KFA, Julich The registration fee is $40, and partial support is available for students. Persons interested in attending should reply to: e-mail: boehm@slater.cem.msu.edu (Randall C. Boehm, Scientist) U.S. mail: Professor T. A. Kaplan Dept. of Physics & Astronomy Michigan State University East Lansing, MI 48824, USA From CHEM86@Jetson.UH.EDU Thu Apr 28 17:32:19 1994 Received: from Rosie.UH.EDU for CHEM86@Jetson.UH.EDU by www.ccl.net (8.6.4/930601.1506) id RAA01404; Thu, 28 Apr 1994 17:20:48 -0400 From: Received: from Jetson.UH.EDU by Jetson.UH.EDU (PMDF V4.2-11 #5185) id <01HBPQOCGAAO8Y8Y3P@Jetson.UH.EDU>; Thu, 28 Apr 1994 16:19:08 CDT Date: Thu, 28 Apr 1994 16:19:07 -0500 (CDT) Subject: USENET News Group - NO !!! To: chemistry@ccl.net Message-id: <01HBPQOCLN768Y8Y3P@Jetson.UH.EDU> X-VMS-To: IN%"chemistry@ccl.net" MIME-version: 1.0 Content-type: TEXT/PLAIN; CHARSET=US-ASCII Content-transfer-encoding: 7BIT Netters- > Actually, UseNet news and the mail-list can be intergrated, so people > who do not have usenet news can still get all the info passed into either > list. Many folks have 'digests' where an article is submitted, and will be > posted via news and listserver. Some cases, such articles are moderated, and > in other's they are not. By doing this sort of scheme, you can reach more > people. No, don't do this ! > Of course, this is a double edge sword, since UseNet news has been > in the past abused. (Some mailings have been abused as well, but not as much > as UseNet, since UseNet is more well known than individual mailing lists.) The USENET is at the turning point right now and its future is very uncertain. Those who read newsgroups regularly (especially news.admin.policy, news.admin.misc) know the Usenet has recently been very badly abused by law firm Cancer & Slime from Phoenix, AZ. These lawyers sent their commercial trash to over 5000 inappropriate newsgroups and threatened the network connection provider with lawsuit after their account was revoked. If they win then millions of different companies will use it as legal precedent and the whole Usenet will be "carpet bombed" with commercial advertisements. Of course the S/N ratio will go down to zero, which effectively destroy the Usenet. So please, think TWICE before you vote for CCL newsgroup - it will not be as safe as mailing list. > At this least, perhaps ccl.net should post an 'ad' once a month, for > this mailing list, so that everyone who reads that group will know about this > list. No, don't do it (for the same reasons) !! --- Robert Fraczkiewicz Dept. of Chemistry University of Houston --- "It is also a good rule not to put too much confidence into experimental results until they have been confirmed by Theory" Sir Arthur Eddington From ZOEBISCH@CRVAX.SRI.COM Thu Apr 28 17:34:17 1994 Received: from CRVAX.SRI.COM for ZOEBISCH@CRVAX.SRI.COM by www.ccl.net (8.6.4/930601.1506) id QAA00982; Thu, 28 Apr 1994 16:43:19 -0400 Date: Thu, 28 Apr 94 13:42:39 PDT From: ""Eve Zoebisch"" To: CHEMISTRY@ccl.net Subject: Semi-empirical methods revisited Message-Id: <9951665.4287052160.ZOEBISCH@CRVAX.SRI.COM> Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 8BIT Semi-empirical methods revisited. In the discussion about semi-empirical methodology, parameterization, methods used in the past, and the need for improved methods, Holder espouses the values of one general method for a given level of approximation whereas Cramer, Paneth and others would appreciate a suite of methods optimized for different problems. As a method developer I find I agree with both viewpoints since, in practice, both are important as this long winded argument will attempt to show. In the development of AM1, one of the first approaches tried was to remove the dipole moments from the basis set in the expectation that the heats of formation would improve. We were very surprised to see negligible improvement in heats of formation whereas the dipole moments no longer made chemical sense. It was clear why this was the case. Assume the dipole moments are irrelevant and randomly assign charges to the atoms (i.e. randomly assign occupation of the atomic orbitals). Clearly these charges would not produce a good description of the electronic structure of the molecule and the heats of formation which are calculated from the density matrix would be poor. In order to provide a good estimate of the energy it is necessary to have an optimal description of the electronic distribution. The most direct and available experimental evidence of electronic distribution was dipole moment and ionization potentials. Other evidence routinely used included the angle in biphenyl, the angle of :CH2 and the relative bond lengths in acetylene. Examination of calculated results compared to experimental data indicated that correlation energy was both important and handled reasonably well within the formalism used. A first order argument of how correlation energy is incorporated was developed in 87. I am glad to see Martin has developed a more rigorous derivation. Given that correlation energy was not the largest source of error, it should be possible to use experimental data to deduce a description of the density matrix. Approximately 2/3 of the time spent developing AM1 parameters was devoted to reproduce data indicative of appropriate electron density distribution. This excessive attention was intended to produce the best possible correlated electron density. Unfortunately the effort was hindered by the approximations in the method. In particular the lack of 3 and 4 center terms (terms describing bond-bond repulsion) and the resulting errors made the effort difficult. At this point it is not possible to know how successful this endeavor was. Literature on ab- initio calculations indicate a high level of correlation is needed before one reproduces the relevant experimental data. I have been hesitant to discuss this aspect until there are appropriate first principle calculations with high level correlation to prove or disprove the appropriate description of electron density and correlation effects. During this stage all data was relevant and provided a clue as to where the model was correct and where it was wrong. The routine day was to minimize the error function in parameter space, compare the resulting parameters with previous sets, deduce how the changes in parameters would change the electronic structure of molecules and propose experimental data which could be found in the library which would clearly demonstrate the strengths and weaknesses of each parameter set. The resulting information was used to propose a new search direction in parameter space. At this stage different parameters sets appeared to be different minima in the error surface. The intent was to determine which minima (which sets of parameters) produce models which most closely resembled chemistry. By far the most difficult part of this procedure was to propose experimental data which would clearly show the differences between two sets of parameters, a task which depends predominantly on chemical intuition. Every method developer using an approach which is not an exact solution of the Schroedinger Equation faces this task independent of the speed of the computer, the size of the basis set, or the search algorithm used. Up to this point I agree with Andy Holder that a method which is general is important. Any data which aids the search and characterization of the error surface is valuable and systems which are in error are an important indicator of where the method is weak. Indeed it was common for a correction implemented to improve one error to improve results for numerous other, seemingly unrelated, systems. One would expect this to be true if the error function is non-linear (resulting in multiple minima) and the method is, to an approximation, correct as Martins work indicates is the case. As a result, the insistence on generality improves the method for all problems as expected for equations which are approximately correct. However as one considers the errors in the method the situation changes. For the optimal sets of parameters mentioned above, different sets represent different distribution of errors. Once the error space is characterized, pragmatic concerns prevail and a parameter set is chosen which minimizes the different errors. It is inappropriate to state that the parameters on, for example, nitrogen are wrong. The parameters chosen are those which reproduced experimental data and it is not possible for them to be wrong. However there may be a difference in opinion on which data is important and particular systems (e.g. nitrogens involved in pi bonding) may have been over emphasized. Personally I would have preferred to maintain a model with an optimal description of the electron density. However most users are interested in heats of formation and the correct angle in biphenyl, among other features, was lost when the method was optimized for heats of formation. With a few notable exceptions, at the time the method was released I was aware of all the errors in AM1 which have crossed my desk since. One of the errors I was not aware of was the interaction between oxygens in water. J. Stewart found this bug and it was thought to have been corrected but apparently it wasnÕt. With these few exceptions, the errors in AM1 were a compromise and an improvement in one area resulted in worse results for another. IÕm not convinced new data and larger molecules would result in a significant improvement. It may be preferable to develop a better (albeit more expensive) approximation such as MNDO/D and SAM1. A better method would lower the errors which are responsible for the lack of generality of a method. Disregarding the above, there is another issue at stake. There is a minor inconsistency in the equations used in AM1 that was found in 87. I have long suspected that correction of this would produce a large enough improvement to justify a cleaner version of the method. I am currently a user and, as a user, I recognize that generating a suite of programs for use in different problems has merit within the concessions to generality mentioned above about the characterization of the error surface. While the 10 year gap does not permit me to remember all the trade-offs made in AM1, I believe the following suite of parameter sets to be possible: -an improved handling of -NO2 groups and heteroatoms involved in pi systems (amide bond) with laughable results for bulk water where there is a strong attraction between oxygen atoms. -improved heats of formation of closed shell, ground state systems with vanishing activation barriers for some radical reactions (indicative of a problem for all reactions) -improved description of electronic properties (spectra, angles, etc.) at the expense of heats of formation. -improved bulk water with loss of -NO2 groups. The amide bond was not tested in this minimum and the effect on the amide bond is not known.. Note: In my recollection, all reasonable sets of parameters gave rotational barriers which were low and the set used was one of the best in this regard. Any significant change in the method would probably have a negative impact on transition states. I would prefer not to see a proliferation of groups developing parameters for specific experiments which one sees in force field work. In MM the correlation between the geometry and the equations is straight forward with few ambiguities. Yet there are still problems with reproducibility from one group to the next and the source of parameters in published work is often not known (often obtained from a friend working with similar functional groups). With methods as ambiguous as semi-empirical functions the problem would be greatly amplified. A small change in one part of a molecule has large effects on totally unrelated systems as seen with -NO2 groups and water mentioned above. As a result an empirical method should be fully characterized (characterization is more difficult in semi-empirical work than in MM) before it can be used in published work. If the suite mentioned above is to be generated, it should be a group effort with common standards of generality, where excessive amounts of chemical intuition is used to ascertain the strengths and weaknesses of the method and these strengths and weaknesses are clearly stated and published before the methods are used. When I have considered all aspects, the effort required for careful method development and characterization, the ambiguity of correct incorporation of correlation energy, the need for more accurate methods, and the likelyhood of obtaining that accuracy within the approximations made in the NDDO approximation, I have generally considered it to be of greater utility to create new methods and not rehash old approximations. E. G. Zoebisch eve@amethyst.sri.com