From owner-chemistry@ccl.net Fri Apr 27 15:34:00 2007 From: "Isaac Bersuker bersuker * mail.cm.utexas.edu" To: CCL Subject: CCL:G: large imaginary frequency in coronene when diffuse Message-Id: <-34149-070427101006-29109-1oayn+DcuXTPNn4vRaCnRg-*-server.ccl.net> X-Original-From: Isaac Bersuker Content-Type: multipart/alternative; boundary="------------030602070007050809090704" Date: Fri, 27 Apr 2007 08:09:47 -0500 MIME-Version: 1.0 Sent to CCL by: Isaac Bersuker [bersuker^^mail.cm.utexas.edu] This is a multi-part message in MIME format. --------------030602070007050809090704 Content-Type: text/plain; charset=KOI8-R; format=flowed Content-Transfer-Encoding: 7bit Dear ALL in this discussion, Puckering of the planar systems under consideration (as any other distortion of high-symmetry configuration in nondegenerate states) is a pseudo Jahn-Teller effect (sufficiently strong admixing of appropriate excited states under the distortion; see, e.g., I. B. Bersuker, The Jahn-Teller Effect, Cambridge University Press, Cambridge, UK, 2006), and as such its numerical computation depends on how well the corresponding excited states are presented in the basis set. The most influential excited states in this effect can be evaluated qualitatively involving symmetry considerations... Dr. Isaac B. Bersuker Institute for Theoretical Chemistry The University of Texas at Austin Chem & Biochem Department 1 University Station A5300 Austin, TX 78712-0165 Phone: (512) 471-4671; Fax: (512) 471-8696 E-mail: bersuker!A!cm.utexas.edu http://www.cm.utexas.edu/directory/isaac_bersuker/ cwannere^_^chem.uga.edu wrote: > Sent to CCL by: cwannere[*]chem.uga.edu > Dear Dr. Goumans, > > Prof. Schleyer's response to your mail is attached below. > > Best wishes, > Chait > > Dear Dr. Goumans > > Our paper may answer your question: > > Popular Theoretical Methods Predict Benzene and Arenes To Be Nonplanar. D. > Moran, A. C. Simmonett, F. E. Leach III, W. D. Allen, P. v. R. Schleyer, H. > F.Schaefer III J. Am. Chem. Soc. 2006, 128(29), 9342-9343. > > Please let us know what you find out. > > Sincerely, > Paul Schleyer > > >> Sent to CCL by: Fedor [t.goumans() ucl.ac.uk] >> Dear CCl-ers, >> >> When the frequencies are calculated with diffuse functions (6-31+G*) for >> coronene there is a large imaginary frequency corresponding to a puckering >> motion of the atoms in the inner ring, although it does not appear to be a >> first order saddle point. >> >> I have tried to understand what gives rise to this puzzling feature, so I >> have >> tried several things: >> >> * The large imaginary frequency arises for HF, DFT (pw91) as well as for >> hybrid >> DFT (B3LYP,B97-1,MPWB1K). Its magnitude is between 700 and 400 imaginary >> wavenumbers. >> * The wavefunction is stable to all the perturbations that are considered >> with >> gaussian's Stable keyword. >> * The imaginary frequency is observed for both G03 and GAMESS-UK. >> * Symmetry-lowering gives higher-energy structures (nosymm, c2v, c2). >> * Intrinsic reaction coordinate following likewise gives rise to >> higher-energy >> structures. >> * Numerical frequencies also give 1 imaginary frequency. From this >> calculation, >> it is seen that all displacements are higher in energy than the starting >> point, >> the optimised coronene. This gives reason to belief that the D6H structure >> is >> indeed a minimum and not a first-order saddle point. >> * A split basis set (6-31+G* on the central ring, 6-31G* on the peripheral >> rings) either with 6 d-functions or 5 d-functions also gives 1 imaginary >> frequency. With a triple-zeta basis set, however, no imaginary frequency >> is >> observed. >> >> It appears that this imaginary frequency arises from the use of diffuse >> functions only. I think that it may be related to the near-linear >> dependency of >> the basis. >> Has anybody observed similar behaviour, or have a better idea where this >> apparent superfluous imaginary frequency may come from? >> >> Thanks for any help, >> kind regards, >> >> Fedor Goumans> > > --------------030602070007050809090704 Content-Type: text/html; charset=KOI8-R Content-Transfer-Encoding: 7bit Dear ALL in this discussion,

Puckering of the planar systems under consideration (as any other distortion of high-symmetry configuration in nondegenerate states) is a pseudo Jahn-Teller effect (sufficiently strong admixing of appropriate excited states under the distortion; see, e.g., I. B. Bersuker, The Jahn-Teller Effect, Cambridge University Press, Cambridge, UK, 2006), and as such its numerical computation depends on how well the corresponding excited states are presented in the basis set. The most influential excited states in this effect can be evaluated qualitatively involving symmetry considerations...
Dr. Isaac B. Bersuker
Institute for Theoretical Chemistry
The University of Texas at Austin
Chem & Biochem Department
1 University Station A5300
Austin, TX 78712-0165
Phone: (512) 471-4671; Fax: (512) 471-8696
E-mail: bersuker!A!cm.utexas.edu
http://www.cm.utexas.edu/directory/isaac_bersuker/


cwannere^_^chem.uga.edu wrote: 
Sent to CCL by: cwannere[*]chem.uga.edu
Dear Dr. Goumans,

Prof. Schleyer's response to your mail is attached below.

Best wishes,
Chait

Dear Dr. Goumans

Our paper may answer your question:

Popular Theoretical Methods Predict Benzene and Arenes To Be Nonplanar. D.
Moran, A. C. Simmonett, F. E. Leach III, W. D. Allen, P. v. R. Schleyer, H.
F.Schaefer III J. Am. Chem. Soc. 2006, 128(29), 9342-9343.

Please let us know what you find out.

Sincerely,
Paul Schleyer

  
Sent to CCL by: Fedor [t.goumans() ucl.ac.uk]
Dear CCl-ers,

When the frequencies are calculated with diffuse functions (6-31+G*) for
coronene there is a large imaginary frequency corresponding to a puckering
motion of the atoms in the inner ring, although it does not appear to be a
first order saddle point.

I have tried to understand what gives rise to this puzzling feature, so I
have
tried several things:

* The large imaginary frequency arises for HF, DFT (pw91) as well as for
hybrid
DFT (B3LYP,B97-1,MPWB1K). Its magnitude is between 700 and 400 imaginary
wavenumbers.
* The wavefunction is stable to all the perturbations that are considered
with
gaussian's Stable keyword.
* The imaginary frequency is observed for both G03 and GAMESS-UK.
* Symmetry-lowering gives higher-energy structures (nosymm, c2v, c2).
* Intrinsic reaction coordinate following likewise gives rise to
higher-energy
structures.
* Numerical frequencies also give 1 imaginary frequency. From this
calculation,
it is seen that all displacements are higher in energy than the starting
point,
the optimised coronene. This gives reason to belief that the D6H structure
is
indeed a minimum and not a first-order saddle point.
* A split basis set (6-31+G* on the central ring, 6-31G* on the peripheral
rings) either with 6 d-functions or 5 d-functions also gives 1 imaginary
frequency. With a triple-zeta basis set, however, no imaginary frequency
is
observed.

It appears that this imaginary frequency arises from the use of diffuse
functions only. I think that it may be related to the near-linear
dependency of
the basis.
Has anybody observed similar behaviour, or have a better idea where this
apparent superfluous imaginary frequency may come from?

Thanks for any help,
kind regards,

Fedor Goumans>