From ferenc ^%at%^ rchsg8.chemie.uni-regensburg.de Mon Oct 14 04:29:24 1996 Received: from comsun.rz.uni-regensburg.de for ferenc.,at,.rchsg8.chemie.uni-regensburg.de by www.ccl.net (8.8.0/950822.1) id DAA21188; Mon, 14 Oct 1996 03:53:32 -0400 (EDT) Received: from rchsg8.chemie.uni-regensburg.de by comsun.rz.uni-regensburg.de with SMTP id AA03051 (5.65c/IDA-1.4.4 for ); Mon, 14 Oct 1996 09:53:26 +0100 Received: by rchsg8.chemie.uni-regensburg.de (931110.SGI/URRZ-Sub-1.5-irix) (for CHEMISTRY \\at// www.ccl.net) id AA09717; Mon, 14 Oct 96 09:52:37 +0200 Date: Mon, 14 Oct 96 09:52:37 +0200 From: ferenc # - at - # rchsg8.chemie.uni-regensburg.de (Ferenc Molnar) Message-Id: <9610140752.AA09717*- at -*rchsg8.chemie.uni-regensburg.de> To: CHEMISTRY*- at -*www.ccl.net Subject: halomethanes Dear Netters: A few days ago I turned to the CCL with the following questions: Original request: > Dear Netters: > > I would like to calculate the optimized structures and > normal modes for a set of related compounds (halomethanes). > > Cl2-C-F2 (Dichlorodifluoromethane) > / \ > Cl-C-F2* Cl2-C-F2+ > (radical) (cation) > / \ > Cl-C-F2+ C-F2 > (cation) (carbene) > \ > C-F > >What type of basis-set would you recommend, that >treats all of these species in a balanced way? > >My idea was to use polarization and diffuse functions >to catch the ionic or radical character of these species. > >I belive, that Hartree-Fock (HF) will do a poor job for some >of these molecules and one has to include electron-correlation >even during optimization! Do you think that it is sensible >to start from a HF minimum structure and to reoptimze with MP2? > >Calculating normal modes with MP2 will be quite expensive >in terms of CPU and disk usage! Any idea about the "precision" >that can be expected from such a calculation? > >I have little experience with the calculation of ionic or >radical species and every comment, hint, or suggestion >is very much appreciated! I will summarize all the responses. I think it is time to summarize the replies. I am very grateful for the valuable information I obtained from: Dr. Luigi Cavallo, Dr. Peter R. Schreiner, Errol Lewars, and Russell D. Johnson III. Their original messages will be appended to this posting. Basically, I decided to compare three levels of theory (HF and Post-HF) for the problem stated in the original posting: 1) QCISD/6-311G(d,p) 2) MP2/6-311++G(d,p) 3) B3LYP/cc-pVTZ The results of these calculations will be compared to available experimental data (geometries). The effect of correlation and/or size of basis set should be clearly visible from the results. I tried to visit the URL given in the fourth reply, but could only get through to the parent page: http://fluid.nist.gov/ everything else seems to be unreachable for me?! Cheers, Ferenc Answers to the original posting: ---------------------------------------------------------------------- On Oct 9, 8:56am, CAVALLO $#at#$ CHEMNA.DICHI.UNINA.IT wrote: > Subject: Re: CCL:halomethanes > > > dear ferenc, > > I tried to make some calculations on substituted haloalkanes, and I found > quite a strange behaviour indeed. > > I tried to optimize the geometry of the following molecules: > CF2Cl-CH3 and the corresponding anion CF2Cl-CH2(-). > Well, the parent molecule gave me any problem, while the anion simply > broke apart. The chlorine atom ran away like an anion and left the > CF2=CH2 alkene. I.E. I obtained the van der waals complex of > 1,1-difluoroethylene and chloride anion. More or less similar > results were obtained with similar molecules. > > I was using classical ab-initio without any correlation. The > basis set I used was 631G + 1 polar + 1 diffuse on all the atoms > (H included). Unhappy of this behaviour, I also tried the simple > mopac and I also tried DFT methods with NL corrections included. > (This last approach should include good correlation effects) but > the results were always the same. > > The only reference I could find on the subject is: > Bernardi et al. Gazz. Chim. Ital. 1990, 120, 301. > > I know that you were asking for cations and radicals instead > of anions, but I think that my experience could be of some > help in warning you with respect to strange behaviours in > haloalkanes. > > yours > luigi > > ------------------------------ > Dr. Luigi Cavallo > Dept. Of Chemistry > Univ. Of Naples > ITALY > Email cavallo -x- at -x- chemna.dichi.unina.it > ------------------------------ >-- End of excerpt from CAVALLO $#at#$ CHEMNA.DICHI.UNINA.IT On Oct 9, 9:12am, Peter R. Schreiner wrote: > Subject: halomethanes > > > I would like to calculate the optimized structures and > > normal modes for a set of related compounds (halomethanes). > > > > Cl2-C-F2 (Dichlorodifluoromethane) > > / \ > > Cl-C-F2* Cl2-C-F2+ > > (radical) (cation) > > / \ > > Cl-C-F2+ C-F2 > > (cation) (carbene) > > \ > > C-F > > > > What type of basis-set would you recommend, that > > treats all of these species in a balanced way? > > > > My idea was to use polarization and diffuse functions > > to catch the ionic or radical character of these species. > > > > I belive, that Hartree-Fock (HF) will do a poor job for some > > of these molecules and one has to include electron-correlation > > even during optimization! Do you think that it is sensible > > to start from a HF minimum structure and to reoptimze with MP2? > > > > Calculating normal modes with MP2 will be quite expensive > > in terms of CPU and disk usage! Any idea about the "precision" > > that can be expected from such a calculation? > > > Dear Ferenc, > > The best compromise is probably DFT, preferrably B3LYP with a flexible > basis set, say 6-311+G* for geometry optimizations. For energies, > you will need a better basis for very accurate results. Others and > my experience would favor correlation-consistent basis sets of > triple zeta quality (e.g., cc-pVTZ) or higher, if you can afford it. > Ideally, you'd used CCSD(T) for the single points, but this may be too > expensive. Thus, the B3LYP/cc-pVTZ//B3LYP/6-311+G* + ZPVE should > be an acceptable compromise. > > For a mini-review on the performance of various methods with carbenes > see: J. Org. Chem. 1996, 61, 7030. > > Hope this helps, > Peter > > > -- > Dr. Peter R. Schreiner Computer-Chemie-Centrum > prs(+ at +)organik.uni-erlangen.de Universitaet Erlangen-Nuernberg > Phone: +49-(0)9131-856533 Naegelsbachstr. 25 > FAX: +49-(0)9131-856566 D-91052 Erlangen, Germany > > NOTE: NEW ADDRESS from November 1, 1996: > > Institut fuer Organische Chemie > Universitaet Goettingen > Tammannstr. 2 Phone: +49-(0)551-393291 > D-37077 Goettingen, Germany FAX: +49-(0)551-399475 > > http://www.ccc.uni-erlangen.de/ecc/private > -- > Dr. Peter R. Schreiner Computer-Chemie-Centrum > prs $#at#$ organik.uni-erlangen.de Universitaet Erlangen-Nuernberg > Phone: +49-(0)9131-856533 Naegelsbachstr. 25 > FAX: +49-(0)9131-856566 D-91052 Erlangen, Germany > > NOTE: NEW ADDRESS from November 1, 1996: > > Institut fuer Organische Chemie > Universitaet Goettingen > Tammannstr. 2 Phone: +49-(0)551-393291 > D-37077 Goettingen, Germany FAX: +49-(0)551-399475 > > http://www.ccc.uni-erlangen.de/ecc/private >-- End of excerpt from Peter R. Schreiner On Oct 9, 10:21am, E. Lewars wrote: > Subject: HALOMETHANES > Hello, some useful refs are: > 1. Theoretical Enthalpies of Formation of CHmCln > : Neutral Molecules and Cations > C. F. Rodrigues, D. K. Bohme, A. C. Hopkinson > J Phys Chem 1996, _100_ 2942-2949 > 2. Photochemical Isomerization of Dichloromethane in Argon Matrices > J Am Chem Soc 1990, _112_ 5117-5122. > Other papers by Hopkinson, in JPC and JACS, in the last 10 years, may also > be helpful. > Good Luck > ==== > Errol Lewars > === >-- End of excerpt from E. Lewars On Oct 9, 12:09pm, Russ Johnson wrote: > Subject: halomethane structures > Dear Ferenc, > First , there is some information on structures of fluoro methanes > and radicals at: > http://fluid.nist.gov/~drb/cgi/SpeciesData.html > > I would recommend a density functional method, as I've found it usually > gives very good geometries and frequencies for radicals and cations. Large > basis sets are usually not necessary so that B3LYP/6-31G* should > do quite well. > > You may have trouble with Cl2-C-F2+ , as both CF4+ and CCl4+ have non- > classical structures, they are more loosely bound complexes such as > CF3+ --- F. > > Good luck, > Russ > > > > > Russell D. Johnson III > Research Chemist > Physical and Chemical Properties Division > National Institute of Standards and Technology > Gaithersburg, MD 20899 > voice 301+975-2513 fax 301+975-3670 > email: russell.johnson ":at:" nist.gov >-- End of excerpt from Russ Johnson Ferenc Molnar --------------------------------------------------------------------------- Institut fuer Physikalische und Theoretische Chemie - Lehrstuhl Prof. Dick - Tel.: (+49) 941 943-4466 /-4486 Universitaet Regensburg Fax.: (+49) 941 943-4488 Universitaetsstrasse 31 D-93053 Regensburg Deutschland / Germany --------------------------------------------------------------------------- EMail (SMTP): Ferenc.Molnar $#at#$ chemie.uni-regensburg.de --------------------------------------------------------------------------- Those who do not archive the past are condemned to retype it! -- Garfinkel & Spafford, Practical Unix Security ---------------------------------------------------------------------------