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From: "Xavier ASSFELD" <Xavier.Assfeld -()- cbt.uhp-nancy.fr>
To: "Karla Tersago" <karla.tersago -()- ua.ac.be>, <chemistry -()- ccl.net>
Subject: RE: conflict between energy and imaginary frequency
Date: Mon, 6 Jun 2005 17:04:05 +0200
Message-ID: <NMEDKFNKILGNCLLLEKCPKENICCAA.Xavier.Assfeld -()- cbt.uhp-nancy.fr>
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Dear,

there are two possible explainations. The first one, as you mentioned is the
numerical noise due to the grid of integration. The cure is to use a
"better" grid! Is it possible?
The second possibility is intramolecular BSSE. Look at the work of Franck
Jensen Chem. Phys. Lett. 261 (1996) 633.
Yours.
                               ...Xav

Pr. Xavier Assfeld             Xavier.Assfeld -()- cbt.uhp-nancy.fr
Chimie et Biochimie theoriques T: (33) 3 83 68 43 82
Faculte des Sciences           F: (33) 3 83 68 43 71
54506 Vandoeuvre, France       http://www.lctn.uhp-nancy.fr

  -----Message d'origine-----
  De : Computational Chemistry List [mailto:chemistry-request -()- ccl.net]De la
part de Karla Tersago
  Envoye : lundi 6 juin 2005 11:35
  A : chemistry -()- ccl.net
  Objet : CCL:conflict between energy and imaginary frequency


  Dear CCL'ers,

  When I perform a geometry optimization, with frequency calculation of a
certain molecule with Gaussian03, I have the following problem:
  Cs symmetry: imaginary frequency of -20 cm-1, so this is transition state
structure.
  C1 symmetry: no imaginary frequencies, so it is a minimum on the potential
energy surface. It's lowest frequency is 27 cm-1.
  I checked the normal modes of both structures and the imaginary frequency
of the Cs form and the lowest frequency of the C1 form correspond to the
same normal mode.
  The problem is that energy of the optimized structured shows that the Cs
form has a lower energy (it is stabilized by 0.02 kcal/mol) than the C1
form.

  How can it be that a transition state has a lower energy than a minimum?

  The calculations were done with B3LYP/6-311+G*
  opt=verytight int=ultrafine freq

  As the data conflict, I thought it might be a problem with some
thresholds, so I tried to set better thresholds with:
  Iop(3/27=15) and Iop(3/29=15)

  I also tried iop(3/32=x) in combination with the above set options, but
for x=3,4,5 the scf did not converged (even not if I put MaxCycle on 500).

  Does anybody have any suggestions on how I can solve this?

  Best regards,

  Karla

--
----------------------------------------------------------------------------
-
Karla Tersago
Structural Chemistry Group, Department of Chemistry
University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
E-mail: karla.tersago -()- ua.ac.be /Phone:+32(03)8202366/Fax:+32(03)8202310
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-

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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD><TITLE></TITLE>
<META http-equiv=3DContent-Type content=3D"text/html; =
charset=3Dus-ascii">
<META content=3D"MSHTML 6.00.2900.2627" name=3DGENERATOR></HEAD>
<BODY text=3D#000000 bgColor=3D#ffffff>
<DIV><SPAN class=3D451054614-06062005><FONT face=3DArial color=3D#0000ff =

size=3D2>Dear,</FONT></SPAN></DIV>
<DIV><SPAN class=3D451054614-06062005><FONT face=3DArial color=3D#0000ff =

size=3D2></FONT></SPAN>&nbsp;</DIV>
<DIV><SPAN class=3D451054614-06062005><FONT face=3DArial color=3D#0000ff =
size=3D2>there=20
are two possible explainations. The first one, as you mentioned is the =
numerical=20
noise due to the grid of integration. The cure is to use a "better" =
grid! Is it=20
possible?</FONT></SPAN></DIV>
<DIV><SPAN class=3D451054614-06062005><FONT face=3DArial color=3D#0000ff =
size=3D2>The=20
second possibility is&nbsp;intramolecular BSSE. Look at the work =
of&nbsp;Franck=20
Jensen Chem. Phys. Lett. 261 (1996) 633.</FONT></SPAN></DIV>
<DIV><FONT face=3DArial color=3D#0000ff size=3D2><SPAN=20
class=3D451054614-06062005>Yours.</SPAN></FONT></DIV>
<P>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=20
&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <FONT=20
size=3D2>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; ...Xav<BR><BR>Pr. Xavier=20
Assfeld&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;=
&nbsp;=20
Xavier.Assfeld -()- cbt.uhp-nancy.fr<BR>Chimie et Biochimie th&eacute;oriques =
T: (33) 3 83=20
68 43 82<BR>Facult&eacute; des=20
Sciences&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; F: =
(33) 3=20
83 68 43 71<BR>54506 Vandoeuvre, =
France&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <A=20
href=3D"http://www.lctn.uhp-nancy.fr/"=20
target=3D_blank>http://www.lctn.uhp-nancy.fr</A></FONT> </P>
<BLOCKQUOTE dir=3Dltr=20
style=3D"PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #0000ff 2px =
solid; MARGIN-RIGHT: 0px">
  <DIV class=3DOutlookMessageHeader dir=3Dltr align=3Dleft><FONT =
face=3DTahoma=20
  size=3D2>-----Message d'origine-----<BR><B>De&nbsp;:</B> Computational =
Chemistry=20
  List [mailto:chemistry-request -()- ccl.net]<B>De la part de</B> Karla=20
  Tersago<BR><B>Envoy&eacute;&nbsp;:</B> lundi 6 juin 2005 =
11:35<BR><B>&Agrave;&nbsp;:</B>=20
  chemistry -()- ccl.net<BR><B>Objet&nbsp;:</B> CCL:conflict between energy =
and=20
  imaginary frequency<BR><BR></FONT></DIV>
  <P class=3DMsoNormal>Dear CCL&#8217;ers,</P>
  <P class=3DMsoNormal><O:P></O:P>When I perform a geometry =
optimization, with=20
  frequency calculation of a certain molecule with Gaussian03, I have =
the=20
  following problem:<BR><O:P></O:P>Cs symmetry: imaginary frequency of =
-20=20
  cm<SUP>-1</SUP>, so this is transition state structure.<BR>C1 =
symmetry: no=20
  imaginary frequencies, so it is a minimum on the potential energy =
surface.=20
  It&#8217;s lowest frequency is 27 cm<SUP>-1</SUP>.<BR>I checked the =
normal modes of=20
  both structures and the imaginary frequency of the Cs form and the =
lowest=20
  frequency of the C1 form correspond to the same normal mode.<BR>The =
problem is=20
  that energy of the optimized structured shows that the Cs form has a =
lower=20
  energy (it is stabilized by 0.02 kcal/mol) than the C1=20
  form.<O:P>&nbsp;</O:P></P>
  <P class=3DMsoNormal>How can it be that a transition state has a lower =
energy=20
  than a minimum?<O:P>&nbsp;</O:P></P>
  <P class=3DMsoNormal>The calculations were done with=20
  B3LYP/6-311+G*<BR>opt=3Dverytight int=3Dultrafine =
freq<O:P>&nbsp;</O:P></P>
  <P class=3DMsoNormal>As the data conflict, I thought it might be a =
problem with=20
  some thresholds, so I tried to set better thresholds =
with:<BR>Iop(3/27=3D15) and=20
  Iop(3/29=3D15)<O:P>&nbsp;</O:P></P>
  <P class=3DMsoNormal>I also tried iop(3/32=3Dx) in combination with =
the above set=20
  options, but for x=3D3,4,5 the scf did not converged (even not if I =
put MaxCycle=20
  on 500).<O:P>&nbsp;</O:P></P>
  <P class=3DMsoNormal>Does anybody have any suggestions on how I can =
solve=20
  this?<O:P>&nbsp;</O:P></P>
  <P class=3DMsoNormal>Best regards,</P>
  <P class=3DMsoNormal>Karla</P><PRE class=3Dmoz-signature =
cols=3D"72">--=20
-------------------------------------------------------------------------=
----
Karla Tersago
Structural Chemistry Group, Department of Chemistry
University of Antwerp, Universiteitsplein 1, B-2610 Antwerp, Belgium
E-mail: <A class=3Dmoz-txt-link-abbreviated =
href=3D"mailto:karla.tersago -()- ua.ac.be">karla.tersago -()- ua.ac.be</A> =
/Phone:+32(03)8202366/Fax:+32(03)8202310=20
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