From krys.radacki@ac.rwth-aachen.de Mon Jul 13 04:33:13 1998 Received: from mail.rwth-aachen.de (mail.RWTH-Aachen.DE [137.226.144.9]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id EAA06362 Mon, 13 Jul 1998 04:33:08 -0400 (EDT) Received: from ac.rwth-aachen.de (pae102.ac.RWTH-Aachen.DE) by mail.rwth-aachen.de (PMDF V5.1-10 #30440) with ESMTP id <01IZCKFE07BG000C35@mail.rwth-aachen.de> for CHEMISTRY@www.ccl.net; Mon, 13 Jul 1998 10:30:38 +0200 Date: Mon, 13 Jul 1998 08:28:49 +0000 From: Krzysztof Radacki Subject: summary: basis functions in LaTeX Sender: root@mail.rwth-aachen.de To: CCL Message-id: <35A9C541.70059ABA@ac.rwth-aachen.de> Organization: Inst.Inorg.Chem., RWTH Aachen, Germany MIME-version: 1.0 X-Mailer: Mozilla 4.05 [en] (X11; I; Linux 2.1.99 i586) Content-type: text/plain; charset=us-ascii Content-transfer-encoding: 7bit I'd like to thanks all who answerd on my question. >>I'm trying to formate table with some basis fuctions in first column. >>When I type: >> >>{\centering \begin{tabular}{|c|c|c|c|c|c|c|} >>\hline ... >>What should I write to obtain output with '/' in the same position in >>cell? Only in first two houres after sending my question I've obtained 13 answers. Most of them was something like incresing amount of columns and useing '/' as column separator: \centering \begin{tabular}{|r@{/}l|c|c|c|c|c|c|} thanks ones more :) -- Krzys Radacki _________________________---------------------------------------------------- ------------------------- e-mail: Krys.Radacki@ac.RWTH-Aachen.DE --- ----------------------------------------------------------------------------- From muhlbach@chemie.uni-wuerzburg.de Mon Jul 13 10:05:44 1998 Received: from wrzx07.rz.uni-wuerzburg.de (wrzx07.rz.uni-wuerzburg.de [132.187.1.7]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id KAA10119 Mon, 13 Jul 1998 10:05:43 -0400 (EDT) Received: from wocx04.chemie.uni-wuerzburg.de (wocx13.chemie.uni-wuerzburg.de [132.187.64.13]) by wrzx07.rz.uni-wuerzburg.de (8.8.8/8.8.8) with SMTP id QAA18487 for ; Mon, 13 Jul 1998 16:05:26 +0200 (MET DST) Received: by wocx04.chemie.uni-wuerzburg.de (940816.SGI.8.6.9/uniwue-C-3.0) id PAA18000; Mon, 13 Jul 1998 15:59:35 +0200 Date: Mon, 13 Jul 1998 15:59:34 +0200 (MDT) From: Joerg Muehlbacher X-Sender: muhlbach@wocx13 To: CCL Subject: CCL: MM3-Bug ? Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Dear CCL'ers, I've a problem with MM3 (Sybyl-Modul): While computing a dynamics-calculation, the abolute configuration of my molecul changed from 'R' to 'S'. (Time p. Step = 0.5fs, T = 300K, Temp.Coup.Fact = 30fs, No Shake was used.) Is this a MM3-Bug or a problem caused by my molecular dynamics parameters ? Cheers, Joerg Muehlbacher _________________________________________________________________________ Joerg Muehlbacher Institut fuer Organische Chemie Computational Chemistry Group phone: +49-(0)931-888-4750 Universitaet Wuerzburg fax : +49-(0)931-888-4755 Am Hubland mail : muehlbacher@chemie.uni-wuerzburg.de D-97074 Wuerzburg _________________________________________________________________________ From d.pender@surrey.ac.uk Mon Jul 13 11:53:39 1998 Received: from mailc.surrey.ac.uk (mailc.surrey.ac.uk [131.227.100.12]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with SMTP id LAA11831 Mon, 13 Jul 1998 11:53:33 -0400 (EDT) Received: from surrey.ac.uk (actually host pc096.chem.surrey.ac.uk) by mailc.surrey.ac.uk with SMTP-external (PP) with ESMTP; Mon, 13 Jul 1998 16:53:25 +0100 Message-ID: <35AA2E92.D5531A34@surrey.ac.uk> Date: Mon, 13 Jul 1998 16:58:10 +0100 From: Dave Organization: University of Surrey X-Mailer: Mozilla 4.04 [en] (Win95; I) MIME-Version: 1.0 To: chemistry@www.ccl.net CC: Peter Karadakov Subject: Summary:Negative eigenvalues in IRC Calcn. Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Dear all, Here is a summary of the responses I received regarding my query posted a week ago. Thank you to Patrik Johansson, Stefan Fau, Stephan Graf and Wibke Sudholt for your interest. I was in fact unable to reproduce the error so maybe it was a one off error, albeit a somewhat peculiar one. The problem seems to occur at a change in symmetry of the TS/product. =========> Original Query <========== I have been doing some ab initio calculations recently on the ring opening of cyclobutene using GAUSSIAN94. I have completed an optimisation of the transition state corresponding to the ring opening and formation of the TRANS product (trans-butadiene). To check that the transition state corresponds to the trans conformation an IRC calculation was performed to follow the path in the direction TOWARDS (reverse direction) the trans product. The command line was: >> # RHF/6-31G(d) IRC(CalcFC,Reverse,Stepsize=40,maxpoints=24) The calculation stopped on the 12th point along the path after 5 optimisation steps having failed to converge with this unusual message: >> Optimization stopped. >> -- Wrong number of negative eigenvalues: Desired= 0 Actual=*** This is very peculiar - I have never seen this before. It is highly unlikely that the calculation has 'stumbled upon' another saddle point. Has anyone come across this before? Any reasons/suggestions/ideas would be welcomed. RESPONSES ==========> 1 <========== Hi Dave Your problem sound like one I encountered about a year ago, maybe you've stumbled into a bifurcation point.. If this is the case it would mean that your IRC calc cannot proceed since two alternative ways - truely equal from the calc point of view - are possible, this would for example be possible if the point where your calc crashes has a C2 or Cs symmetry ( or close to ). The way to check and to let the calc. continue is : 1. to perform a freq calc at the IRC point immediately before your calc crashes ( perhaps with a smaller stepsize.) 2. Check the resulting imaginary freqs and see which mode that corresponds to the path you would like to continue along. 3. Move your geometry away from the bifurc point by using the mode above. 4. Perform a new IRC calc from this new geometry. best wishes Patrik ==========> 2 <========== Hi Dave, something went seriously wrong with your IRC. The three stars indicate >999 negative eigenvalues! This is a problem of the actual run and might just vanish on repeating the calculation. By the way, it is advisable to start with the read in structure and hessian matrix of the confirmed TS using IRC(...,readfc,...) and geom=check since this avoids problems due to low numerical accuracy of the input TS structure. If you continue having problems, try to reduce the stepsize and increase the accuracy (using the tight option). Greetings, Stefan ==========> 3 <========== Hi Dave, I had a similar problem during the optimization of saddle points structures. Sometimes G94 stopped with the same message. It seems that there is a bug in the G94 routine which counts the number of negative eigenvalues. Because after testing the structure with a frequency job, I got the correct number of negative eigenvalues. With the OPT keyword is the NoEigenTest option available, which omits the counting of the negative eigenvalues. Unfortunately this option is not listed for the IRC keyword (at least on www.gaussian.com). But ther is maybe an IOp which does the same. Hope this helps, Stephan __________________________________________________________ Dave Pender Tel. 01483 259591 Department of Chemistry Pager. 0336 785185 University of Surrey Guildford Surrey GU2 5XH. ** "The World is a Stage, but the Play is Badly Cast" -- Oscar Wilde ** From boufer@cennas.nhmfl.gov Mon Jul 13 15:15:07 1998 Received: from cennas.nhmfl.gov (cennas.nhmfl.gov [146.201.220.8]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id PAA13845 Mon, 13 Jul 1998 15:15:06 -0400 (EDT) Received: from localhost (boufer@localhost) by cennas.nhmfl.gov (980427.SGI.8.8.8/970903.SGI.AUTOCF) via SMTP id QAA01173 for ; Mon, 13 Jul 1998 16:16:19 -0400 (EDT) Date: Mon, 13 Jul 1998 16:16:19 -0400 (EDT) From: Ahmed Bouferguene To: CHEMISTRY@www.ccl.net Subject: Derivatives of the density matrix Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Greetings all, I wonder if somebody knows where the derivatives of the density matrix with respect to X, Y, Z(of the atoms) are stored in G94. Thanks for your time and help. From elewars@alchemy.chem.utoronto.ca Mon Jul 13 17:52:12 1998 Received: from alchemy.chem.utoronto.ca (alchemy.chem.utoronto.ca [142.150.224.224]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id RAA02317 Mon, 13 Jul 1998 17:52:12 -0400 (EDT) Received: (from elewars@localhost) by alchemy.chem.utoronto.ca (8.7.4/8.7.3) id RAA13779 for chemistry@www.ccl.net; Mon, 13 Jul 1998 17:52:11 -0400 (EDT) Date: Mon, 13 Jul 1998 17:52:11 -0400 (EDT) From: "E. Lewars" Message-Id: <199807132152.RAA13779@alchemy.chem.utoronto.ca> To: chemistry@www.ccl.net Subject: ELECTRON CORRELATION SUMMARY Mon 1998 July 13 Thanks to all who replied to my questions about electron correlation. Here are the answers I got. E. Lewars ==================== Questions Tues, 1998 July 7 SOME QUESTIONS ABOUT ELECTRON CORRELATION AND THE HARTREE-FOCK METHOD Hello, The HF method (HFM), even at the basis set limit, gives an energy which is higher than the exact expectation value of the Hamiltonian, the energy difference being the correlation energy. The higher value of the HF energy is said to be due to overestimation of *potential* energy ("the HF method always underestimates the kinetic energies of the electrons"--Pilar, 2nd ed, p 286), specifically electron-electron repulsion. The HFM is also said to underestimate the coulomb hole ("the coulomb hole is neglected almost completely" -- Pilar, p 296/297) and to overestimate the fermi hole (Pilar 296). So the HFM gives an energy that is too high, because it overestimates el-el potential E ; as far as *kinetic* energy goes, the HFM would give an energy that is too *low*. QUESTIONS: 1) Does anyone question any of the above statements? 2) If the fermi hole is overestimated, should this decrease el-el repulsion, since the fermi hole means a region around each el. unfriendly to other electrons of the same spin--if any two electrons avoid one another they repel one another less; in which case: 3) Shouldn't the neglect of the *coulomb hole* be the real cause of the over- estimation of el-el repulsion? In other words, shold not most of the el-el repulsion in the HFM be between electrons of *opposite* spin (electrons of the same spin avoiding one another because of the Pauli effect (i.e. because of the fermi hole)? 4) Overestimation of the fermi hole is simply a result of using a one- determinant wavefunction--right? 5) Is there a way to see *intuitively* that the HFM must overestimate electron-electron repulsion and underestimate electron kinetic energy? Thanks E. Lewars ======================== ANSWERS: [1] Jul 7 Samuel A. Abrash (75) Re: CCL:QUESTIONS:ELECTRON CORRELATCommand: Read MessageMessage 2/19 from Samuel A. Abrash Jul 07 '98 at 12:10 (noon) X-Sender: sabrash@facstaff.richmond.edu Subject: Re: CCL:QUESTIONS:ELECTRON CORRELATION At 11:42 AM 7/7/98 -0400, you wrote: >Tues, 1998 July 7 > > SOME QUESTIONS ABOUT ELECTRON CORRELATION AND THE > HARTREE-FOCK METHOD > >Hello, > >The HF method (HFM), even at the basis set limit, gives an energy which is >higher than the exact expectation value of the Hamiltonian, the energy >difference being the correlation energy. The higher value of the HF energy is >said to be due to overestimation of *potential* energy ("the HF method always >underestimates the kinetic energies of the electrons"--Pilar, 2nd ed, p 286), >specifically electron-electron repulsion. The HFM is also said to >underestimate the coulomb hole ("the coulomb hole is neglected almost >completely" -- Pilar, p 296/297) and to overestimate the fermi hole (Pilar 296). > > So the HFM gives an energy that is too high, because it overestimates el-el >potential E ; as far as *kinetic* energy goes, the HFM would give an energy >that is too *low*. >5) Is there a way to see *intuitively* that the HFM must overestimate >electron-electron repulsion and underestimate electron kinetic energy? > Intuitively, the Hartree-Fock method has the electron interacting with the average position of the other electron in its two electron orbital. However, when an electron in a two electron orbital is at a given point in space, the wavefunction of the other electron is substantially less isotropic than the wavefunction used in the Hartree fock calculation, and is peaked as far as possible from the position of the electron under consideration. Thus the hartree fock equation has the electron of interest interacting with the other electron at close distances far too much of the time. Since the average radius of interaction of the two electrons in the orbital is smaller than the true value, the electron-electron repulston energy is too high. > E. Lewars >======================== > Samuel A. Abrash Associate Professor Department of Chemistry University of Richmond Richmond, VA 23174 (804) 289-8248 Fax: (804)289-8482 sabrash@richmond.edu "I believe in the open mind, but not so open your brain falls out." ==================== [2] Jul 7 Alan Shusterman (24) Re: CCL:QUESTIONS:ELECTRON CORRELATCommand: Read MessageMessage 3/19 from Alan Shusterman Jul 07 '98 at 9:45 am Date: 07 Jul 98 09:45:57 PDT Subject: Re: CCL:QUESTIONS:ELECTRON CORRELATION To: elewars@alchemy.chem.utoronto.ca I think your 3rd point, repulsion is overestimated between electrons of opposite spin, is correct. HF assigns an electron pair to the same orbital and this must create most of the correlation error. Alan ---------------- Alan Shusterman Department of Chemistry Reed College Portland, OR www.reed.edu/~alan ============= [3] Jul 7 Vitaly Rassolov (62) Re: CCL:QUESTIONS:ELECTRON CORRELATCommand: Read MessageMessage 4/19 from Vitaly Rassolov Jul 7 '98 at 12:02 (noon) X-Sender: rassolov@b.theory.nwu.edu Reply-To: Vitaly Rassolov Subject: Re: CCL:QUESTIONS:ELECTRON CORRELATION Most of the features of electron correlation can be "understood" if one remembers that HF model is equivalent to describing the motion of every electron in the averaged field of the others. For instance, if this field is not averaged, it structure is more complicated and electrons have to do a more complicated movement, thus increasing their kinetic energy (it does take kinetic energy to avoid other electrons!). The same goes for the electron repulsion energy - it should go down. Both of these statements are universal i.e. they apply to all "reasonable" (i.e. no "funny" potentials with non-isolated singularites, etc) systems. The "overestimation" of Fermi hole is en exception. It is either not true, or true only for some specific cases. We know that in dense electron gas the Fermi hole is underestimated, just like a Coulomb one. line 1 [h for help]In fact, they are underestimated in a very similar manner, which is somewhat surprising. One can also see that a triplet state of two-electron system (like He) also has its Fermi hole underestimated by the HF model (the electron repulsion energy should be smaller for the correlated wave function, and there is no Coulomb hole in the system, so the whole effect is in the Fermi hole). To summarize: 1. Yes (with respect to Fermi hole). 2. Yes. 3. Yes. 4. The whole question is probably wrong. 5. The averaged field explains it all. I hope it helps, Vitaly Rassolov. Vitaly Rassolov rassolov@chem.nwu.edu Chemistry Department tel. (847) 491-3423 Northwestern University fax (847) 491-7713 ========== [4] NU 5 Jul 7 Thomas A Adler (70) Re: CCL:QUESTIONS:ELECTRON CORRELATCommand: Read MessageMessage 5/19 from Thomas A Adler Jul 7 '98 at 10:29 am Organization: Albany Research Center, DOE To: "E. Lewars" Date: Tue, 7 Jul 1998 10:29:48 PST Subject: Re: CCL:QUESTIONS:ELECTRON CORRELATION Message-ID: <12371133264@zr.alrc.doe.gov> Dear Dr. Lewars, The best explanation that I have seen for the correlation problem is in Bethe and Salpeter, Quantum Mechanics of One- and Two-Electron Systems. The correlation problem is due to the form of the wave function. The Hartree-Fock method uses only single electron functions, while an exact solution to the Hamiltonian must contain two electron terms. One electron function: U = u(r_1)v(r_2) where r_1 is the distance from the nucleus to electron 1 and r_2 is the distance from the nucleus to electron 2. Two electron function: W = u(r_1)v(r_2)w(r_12) where r_12 is the distance from electron one two electron 2. w(r_12) is missing in the HFM and is the reason the electron-electron potential energy is too high and the kinetic energy is too low. The overestimate in the coulomb term is greater than the underestimate in the exchange term. Therefore the net electron-electron potential is overestimated. The underestimate in the kinetic energy is nearly the same as the net overestimate in the electron-elctron potential. The electron-nuclear potential is nearly correct. (In other words, I do not question the statements from Pilars.) > Tues, 1998 July 7 > > SOME QUESTIONS ABOUT ELECTRON CORRELATION AND THE > HARTREE-FOCK METHOD > Thomas A. Adler Albany Research Center, Department of Energy 1450 Queen Avenue, SW Albany OR 97321-2198 E-mail: adler@alrc.doe.gov (541) 967-5853 ========= [5] N 7 Jul 7 gunnj@CERCA.UMontr (41) Re: CCL:QUESTIONS:ELECTRON CORRELATCommand: Read MessageMessage 7/19 from gunnj@CERCA.UMontreal.CA Jul 7 '98 at 2:22 pm Subject: Re: CCL:QUESTIONS:ELECTRON CORRELATION To: elewars@alchemy.chem.utoronto.ca (E. Lewars) Date: Tue, 7 Jul 1998 14:22:15 -0400 (EDT) X-Mailer: ELM [version 2.4 PL23] Mime-Version: 1.0 Content-Transfer-Encoding: 8bit > > 5) Is there a way to see *intuitively* that the HFM must overestimate > electron-electron repulsion and underestimate electron kinetic energy? I'm not familiar with the literature in this area, but as I read your question I thought about it to see if it made sense, so I'd thought I'd try responding directly to this last point. What is missing from the HFM is the correlation, which corresponds roughly to allowing the electrons to avoid one another. I think this is also what you refer to as the coulomb hole. In that case, it seems obvious that the coulomb repulsion integral between two mean-field orbitals will be necessarily larger than the average of the instantaneous repulsion between two moving electrons. The other effects would seem to be compensating for that. The variational calculation still tries to minimize the energy as best it can, and so it takes more advantage of the Pauli repulsion than it would otherwise, and it uses larger orbitals than it really needs which lowers the kinetic energy. -John. ========== [6] Jul 7 J. Sichel (37) Re: CCL:QUESTIONS:ELECTRON CORRELATCommand: Read MessageMessage 8/19 from J. Sichel Jul 7 '98 at 3:22 pm X-Authentication-Warning: bosoleil.ci.umoncton.ca: sichelj owned process doing - bs Date: Tue, 7 Jul 1998 15:22:17 -0300 (ADT) X-Sender: sichelj@bosoleil.ci.umoncton.ca Reply-To: "J. Sichel" On Tue, 7 Jul 1998, E. Lewars wrote: > SOME QUESTIONS ABOUT ELECTRON CORRELATION AND THE > HARTREE-FOCK METHOD > > 5) Is there a way to see *intuitively* that the HFM must overestimate > electron-electron repulsion and underestimate electron kinetic energy? The exact and HF wave function both obey the virial theorem (Levine Quantum Chem 4/e p.441) =20 That is, =3D -2 and therefore =3D + =3D - .=20 So since the variational theorem guarantees that E(HF) > E(exact), we must have T(HF) < T(exact) and V(HF) > V(exact). John Sichel Universit=E9 de Moncton, NB, Canada ============= From elewars@alchemy.chem.utoronto.ca Mon Jul 13 17:56:41 1998 Received: from alchemy.chem.utoronto.ca (alchemy.chem.utoronto.ca [142.150.224.224]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id RAA02355 Mon, 13 Jul 1998 17:56:41 -0400 (EDT) Received: (from elewars@localhost) by alchemy.chem.utoronto.ca (8.7.4/8.7.3) id RAA13932 for chemistry@www.ccl.net; Mon, 13 Jul 1998 17:56:41 -0400 (EDT) Date: Mon, 13 Jul 1998 17:56:41 -0400 (EDT) From: "E. Lewars" Message-Id: <199807132156.RAA13932@alchemy.chem.utoronto.ca> To: chemistry@www.ccl.net Subject: TWO ELECTRON INTEGRAL ERROR? Monday July 1998 Hello, Comparing some two-electron integrals in the book "Modern Quantum Chemistry", by Szabo and Ostlund (1989) with Gaussian 92 output I find what seem to be discrepancies: ------------ H2 molecule STO-3G bond length = 1.4 a.u. (0.741 A) I give the integrals in the order and the approximate format in which they appear in the book and in the G92 output: Book, page 162 G92 I J K L (11|11)=(22|22) = 0.7746 2 2 2 2 0.7746 (11|22) = 0.5697 2 2 2 1 0.4441 (21|11)=(22|21) = 0.4441 2 1 2 1 0.1485 (21|21) = 0.2970 2 2 1 1 0.2848 What is supposed to correspond to the Book's 0.5697 and 0.2970?? ----------------- HeH+ molecule STO-3G bond length = 1.4632 a.u. (0.7743 A) Book, page 172 G92 (11|11) = 1.3072 (22|11) = 0.6057 2 2 2 2 1.0557 2 2 1 1 0.5908 (21|11) = 0.4373 (22|21) = 0.3118 2 2 2 1 0.4440 2 1 1 1 0.3674 (21|21) = 0.1773 (22|22) = 0.7746 2 1 2 1 0.2243 1 1 1 1 0.7746 What is supposed to match 1.3072? and 0.6057? ....etc.? -------------------- I'm sure I may just be overlooking something _very simple_. But on the surface the numbers do not agree. Is one set of values wrong? Thanks E. Lewars ============================ From 9702029k@lv.levels.unisa.edu.au Mon Jul 13 20:55:22 1998 Received: from zorba.levels.unisa.edu.au (SYSTEM@Zorba.levels.unisa.edu.au [130.220.17.9]) by www.ccl.net (8.8.3/8.8.6/OSC/CCL 1.0) with ESMTP id UAA10028 Mon, 13 Jul 1998 20:55:20 -0400 (EDT) Received: from xiy205359.unisa.edu.au ("port 4854"@XIY205359.Levels.UniSA.Edu.Au) by Levels.UniSA.Edu.Au (PMDF V5.1-10 #27872) with SMTP id <01IZDYJ5NCY69878XC@Levels.UniSA.Edu.Au> for chemistry@www.ccl.net; Tue, 14 Jul 1998 10:25:16 +0930 Received: by xiy205359.unisa.edu.au with Microsoft Mail id <01BDAF12.DE23C440@xiy205359.unisa.edu.au>; Tue, 14 Jul 1998 10:33:40 +0930 Date: Tue, 14 Jul 1998 10:33:37 +0930 From: Josh Bowden <9702029k@lv.levels.unisa.edu.au> Subject: Summary : Mixing basis sets. To: "'chemistry@www.ccl.net'" Message-id: <01BDAF12.DE23C440@xiy205359.unisa.edu.au> MIME-version: 1.0 Content-type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by www.ccl.net id UAA10028 Hello all, Thanks to you who replied. I wrote : >As a continuation of recent discussion on this list about 3-21G vs 6-31G*, can I ask if anyone >has information on mixing basis sets in a calculation. Programs such as CRYSTAL 95 and >HyperChem (probably others as well) allow you to apply different basis to individual atoms. If >the lack of polarization functions ( as stated by cory@chem.ucalgary) is a problem can you >not apply a bigger basis set to 'problem' atoms and reduce the basis of others? >Has anyone looked at this systematically and is there any referencs on this topic? >Are there any problems in this metholodgy (does it have any major downfalls)? Dr. Cory C. Pye (cory@zinc.chem.ucalgary.ca) wrote : >The biggest problem with mixing basis sets is that you run the risk of >obtaining an 'unbalanced' overall basis set. This basically means that the >electronic distribution, compared to the true distribution, is lopsided. >A way to think of this is that if you have a homonuclear diatomic with a >minimal basis set on one atom (A) and a triple zeta valence + pol + dif on >the other atom (B), then, because B has more functions over which to distribute >electron density, you will basically have a dipole moment for this homonuclear >diatomic (more charge on B than A), which is physically unrealistic. > >One should therefore always try to balance the basis set by using similar >types on different atoms. For example (from my own work) in >J. Org. Chem., 60, 2328-9 (1995), J. Org. Chem., 63, 105-112 (1998), and >J. Phys. Chem B, 102, 3564-3573 (1998), we did not have available a >6-31G* basis set for atoms of interest beyond Ar (Br,I,Se,Te,As,Sb,Ge,Sn(x2);Cd) >so we spliced in a Huzinaga basis set (from his book --- >take the minimal basis set with the highest # of primitives in the innermost >shell; split the valence shell (n) to ( (n-1)(1) ); and add a polarization >function provided) to give a SVP type basis set (like 6-31G*). > >On a related note, there is a basis set called 3-21G(N) (by Hehre, I believe) >where the 3-21G* basis set is augmented by nitrogen polarization functions. Dr. Georg Schreckenbach (schrecke@t12.lanl.gov) wrote : >In any case, I think people have used such "locally dense" basis sets a >lot. Typically, you would use the high level basis set on, e.g., the metal >atom AND its nearest neighbors, and smaller basis sets elsewhere. One >reference is a review by Don Chesnut: D. B. Chesnut, in Annual Reports on >NMR Spectroscopy Vol. 29, Academic Press 1994, p. 71. He uses such locally >dense basis sets for NMR calculations, and I believe that he has newer >papers on this as well. > The more recent NMR review by de Dios has similar information (A. >C. de Dios, Prog. NMR Spectros. 29 (1996), 229.) You will find further >references in these reviews. > >Furthermore, and this is slightly off from your question, the idea of using >a higher level of theory for the interesting atoms, and a lower level >elsewhere, has been pursued in the QM/MM methods: In this case, you do >whatever quantum mechanical method you need at the reaction center, and >molecular mechanics at the bulky ligands or solvent or so. The Morokuma >version of this ("ONIOM") is present in GAUSSIAN98, as far as I know. >Others have done such things as well, e.g. T.K.Woo/T.Ziegler. > >Best regards, Georg Robert J. Zellmer (rzellmer@chemistry.ohio-state.edu) wrote : >I think most programs that allow you to put in general basis sets would be >able to do this. I know GAMESS is capable of this and I have done it using >GAMESS. I don't know of any systematic study of doing this, at least not one >that has been published. I know a few years back when I was doing some >calculations on perfluoroethers in conjuction with someone at Dupont they had >determined that d-type polarization functions could be left off the Fluorines >w/o any real affect on the calculations, but they were still needed on the >Oxygen atoms. This might be mentioned in some of the papers published by the >folks at Dupont and I can check if you like. > Stefan Konietzny (konietz@chemie.uni-kl.de) wrote : >Hi! > >I dont know which program you use, but in GAUSSIAN it is possible. > >Try the GEN Keyword instead of of general basis set. > ># hf/gen fopt .... > >After the molecule specification you have to apply the basis to the atoms. >You can do this like this > >H C 0 >6-31+g(d) >**** > >This means every H and C atom has 6-31+g(d). > >But if you use the numbers of the atoms, you can apply different basis >sets to different H (or C, or anything else) atom. > ># hf/gen fopt name=konietz > >h2o > >0 1 >h >o 1 1.1 >h 2 1.1 h 108. > >2 0 >6-31g >**** >1 3 0 >3-21g >**** > >Hope this helps. > Thanks again, Josh Josh Bowden Ian Wark Research Institute University of South Australia E-mail : 9702029k@lv.levels.unisa.edu.au