From genghis {*at*} darkwing.uoregon.edu Mon Oct 14 10:15:14 1996 Received: from darkwing.uoregon.edu for genghis: at :darkwing.uoregon.edu by www.ccl.net (8.8.0/950822.1) id KAA22953; Mon, 14 Oct 1996 10:04:39 -0400 (EDT) Received: (from genghis-!at!-localhost) by darkwing.uoregon.edu (8.7.6/8.7.3) id HAA14711; Mon, 14 Oct 1996 07:04:37 -0700 (PDT) Date: Mon, 14 Oct 1996 07:04:37 -0700 (PDT) From: Dale Braden To: cclpost Subject: Summary: ab initio questions Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Dear CCL, Below are two questions I posted recently, followed by the responses. Thanks to all who responded. 1) The output of a frequency calculation normally includes the mass-weighted nuclear displacements for each normal mode, along with the reduced mass. Does anyone know how to calculate the *absolute* nuclear displacements, given the kind of data available from a frequency calculation by, for example, Gaussian 94? 2) In looking through the literature on calculations for organometallic complexes, I have noticed that polarization functions are often NOT added to the basis set for the transition metal, although they are always added to first-row atoms. Furthermore, for anionic systems, diffuse functions will be added only to the basis set used for the ligand atoms, but not to that for the metal. Now, perhaps calculations using such basis sets will agree well with experiment, but wouldn't this be fortuitous, since the basis set is unbalanced? Do the readers agree with the above practice? ---------------------- From hinsen:~at~:ibs.ibs.frMon Oct 14 06:55:54 1996 Date: Mon, 7 Oct 96 10:47:41 +0100 From: Konrad Hinsen You must divide each displacement by the square root of the mass of the respective atom. ------------------------------------------------------------------------------- Konrad Hinsen | E-Mail: hinsen |-at-| ibs.ibs.fr Laboratoire de Dynamique Moleculaire | Tel.: +33-76.88.99.28 Institut de Biologie Structurale | Fax: +33-76.88.54.94 41, av. des Martyrs | Deutsch/Esperanto/English/ 38027 Grenoble Cedex 1, France | Nederlands/Francais ------------------------------------------------------------------------------- ------------------ From irikura: at :leatherback.nist.govMon Oct 14 06:56:01 1996 Date: Mon, 07 Oct 1996 18:03:22 -0400 From: Karl Irikura I believe that the normal mode vectors reported by Gaussian are generated by (1) diagonalization of the standard mass-weighted hessian, (2) mass un-weighting the resulting orthonormal eigenvectors, (3) re-normalization of the pure displacement vectors. (I think the multiplier required for this normalization step is reported by Gaussian as the reduced mass.) These vectors are not orthogonal. If I recall properly, the ACES II program reports the straight mass-weighted, orthonormal eigenvectors and the GAMESS-US program reports the mass-unweighted (but not re-normalized) vectors. In my limited work (energetics) with organometallic compounds, I have found it important to include polarization functions on the central metal. I don't know the effects of diffuse functions because I've never done calculations on anionic metal systems. Best wishes, Karl Irikura ---------------------------------------------- Dr. Karl K. Irikura Physical and Chemical Properties Division National Institute of Standards and Technology Gaithersburg, MD 20899 voice: 301-975-2510 fax: 301-975-3670 e-mail: karl.irikura # - at - # nist.gov ---------------------------------------------- -------------------- From fredvc #at# esvax.dnet.dupont.comMon Oct 14 06:56:05 1996 Date: Mon, 7 Oct 96 22:49:07 EDT From: fredvc -x- at -x- esvax.dnet.dupont.com My exerience has been that programs are not consistent in what they print as the PED. One expects the coefficients of the mass-weighted displace- ments, i.e, "C" for C * sqrt(m) * q One program I used printed "C" values, another printed "C * sqrt(m)" values. What I do with a new program is run something where the it will clear what is printed, say, HF. From this I can tell what the authors of the code decided to print. I know, I know,... it should always be "C", but I find it best to test eahc code that I run. ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 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 -A_T- 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. <***** ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ -------------------- From hommes.,at,.organik.uni-erlangen.deMon Oct 14 06:56:10 1996 Date: Tue, 8 Oct 1996 21:26:28 +0100 (MET) From: Nico van Eikema Hommes Reply to: hommes;at;derioc1.organik.uni-erlangen.de > 1) The output of a frequency calculation normally includes the > mass-weighted nuclear displacements for each normal mode, along with the > reduced mass. Does anyone know how to calculate the *absolute* nuclear > displacements, given the kind of data available from a frequency > calculation by, for example, Gaussian 94? What you want, if I understand it correctly, is just a diagonalization of the second derivatives matrix. That should be no problem to do. If I remember correctly, both sets of displacements are available from a MOPAC run. > 2) In looking through the literature on calculations for organometallic > complexes, I have noticed that polarization functions are often NOT added > to the basis set for the transition metal, although they are always added > to first-row atoms. Furthermore, for anionic systems, diffuse functions > will be added only to the basis set used for the ligand atoms, but not to > that for the metal. Now, perhaps calculations using such basis sets will > agree well with experiment, but wouldn't this be fortuitous, since the > basis set is unbalanced? Do the readers agree with the above practice? The reason for this habit is practical: polarization for transition metals means adding f-functions. That makes the calculations much more expensive, many programs handle only spd basis sets, and popular codes like g94 can not compute first derivatives for the combination f-functions and ECPs. Yet it does indeed result in an unbalanced basis set and is not a good idea, despite all the literature "support" for it. Augmenting the metal basis set with diffuse functions is a different matter. These are important on electronegative elements, especially for the proper description of lone pairs (and not only for anionic systems), but play little role when added to the metal. In some cases, they may even worsen the result by leading to basis set superposition error, with the metal diffuse functions helping to describe ligand density. Hope this helps. Best wishes, Nico van Eikema Hommes -- Dr. N.J.R. van Eikema Hommes Computer-Chemie-Centrum hommes- at -ccc.uni-erlangen.de Universitaet Erlangen-Nuernberg Phone: +49-(0)9131-856532 Naegelsbachstr. 25 FAX: +49-(0)9131-856566 D-91052 Erlangen, Germany *************************************************************** Dale Braden Department of Chemistry University of Oregon Eugene, OR 97402 genghis ":at:" darkwing.uoregon.edu