Hi David,<= br>

I agree that for eve= ry TS identified an IRC should be run in order to verify. I have been surpr= ised in the past, and glad I did so! :)

<= /div>

Best,

Am= y

Fro= m: David Gallagher gallagher.da*gmail.com <owner-chemistry-,-cc= l.net>
To: "Austin,= Amy J " <amy_jean_austin-,-yahoo.com>
Sent: Saturday, August 4, 2012 5:09 PM
Subject: CCL: Negative Barrier Height

=0A

=0A =0A=0A =0A =0A

=0A Hi Bhupesh,
=0A
=0A As some other respondents have indicated, if=0A there are no negati= ve vibrations then you have found a (local)=0A energy minimum. A= true transition state is indicated by a single=0A negative vibration.=
=0A
=0A There are some suggested strategies for lo= cating transition states=0A posted at http://cacheresearch.com/= presentations.html=0A (about halfway down the page). Although thes= e were written for=0A MOPAC, the principles apply to most quantum method= s.
=0A
=0A Once you have characterized th= e transition state,=0A you should run an intrinsic reaction coordinate= (IRC) to verify=0A that it does go to the expected reactants and prod= ucts, i.e. to=0A make sure that it belongs to the correct reaction pat= h.
=0A
=0A Good luck.
=0A David Gallagher
= =0A CAChe Research
=0A
=0A
=0A = =0A

On 8/3/2012 7:05 = AM, Dr. Bhupesh Kumar=0A Mishra bhupesh_chem(_)rediffmail.com wrote:
=0A

=0A=

=0A

Sent to CCL by: "Dr. Bhupesh Ku=
mar Mishra" [bhupesh_chem__rediffmail.com]=0ADear All,=0AI am doing some calcul=
ation on reaction mechanism. I have optimized transition states. But the pr=
oblem is that it is characterized by low vibrational frequency (<100 cm-=
1). The calculated barrier heights are negative. Whether it is possible? Ma=
y negative barrier heights for TS are acceptable for understanding of any r=
eaction mechanism?=0A Any suggestions is highly appreciated.=0A=0ASincerely=
=0ABhupesh  Kumar Mishra(Ph.D.)=0AUGC-Dr. D. S. Kothari Post Doctoral Fello=
w=0ADepartment of Chemical Sciences=0ATezpur University=0ATezpur- ASSAM=0AI=
NDIAE-mail to subscribers: CHEMISTRY*|*ccl.net or use:=0A   ==0A=0AE-mail to administr=
ators: CHEMISTRY-REQUEST*|*ccl.net or use=0A=
      http:/=
/www.ccl.net/cgi-bin/ccl/send_ccl_messagehttp://www.ccl.net/chemistry/sub_u=
nsub.shtml=0A=0A=0A=
=0A=0AConferences: http://server.ccl.net/chemi=
stry/announcements/conferences/=0A=0ASearch Messages: http://www.ccl.net/chemist=
ry/searchccl/index.shtmlhttp://www.ccl.net/spammers.txt=0A=0ARTFI: http://w=
ww.ccl.net/chemistry/aboutccl/instructions/=0A=0A=0A=0A

=0A =0A=
=0A

=0A=0A

---790415396-2097169200-1344136174=:13111-- From owner-chemistry@ccl.net Sun Aug 5 02:53:00 2012 From: "Amy J Austin amy_jean_austin|a|yahoo.com" To: CCL Subject: CCL: Negative Barrier Height Message-Id: <-47324-120804234015-29536-eDvGvSaDEJAHdkFnBpJwOQ[*]server.ccl.net> X-Original-From: "Amy J Austin" Date: Sat, 4 Aug 2012 23:40:12 -0400 Sent to CCL by: "Amy J Austin" [amy_jean_austin++yahoo.com] I assumed you meant that you had found a true transition state along your reaction path, indicated by an imaginary (marked negative) frequency. As David points out, if you don't have one negative eigenvalue, then you are not at a saddle point. Best, Amy > "Amy J Austin amy_jean_austin*yahoo.com" wrote: > > Sent to CCL by: "Amy J Austin" [amy_jean_austin||yahoo.com] > > Hello Bhupesh, > > It sounds like a multi-step reaction in which there is an intermediate that is lower in energy than the reactants, and that you have found the transition state for that intermediate, which is also lower in energy than reactants. > > Best, > > Amy > > > > "Dr. Bhupesh Kumar Mishra bhupesh_chem(_)rediffmail.com" wrote: > > > > Sent to CCL by: "Dr. Bhupesh Kumar Mishra" [bhupesh_chem__rediffmail.com] > > Dear All, > > I am doing some calculation on reaction mechanism. I have optimized transition states. But the problem is that it is characterized by low vibrational frequency (<100 cm-1). The calculated barrier heights are negative. Whether it is possible? May negative barrier heights for TS are acceptable for understanding of any reaction mechanism? > > Any suggestions is highly appreciated. > > > > Sincerely > > Bhupesh Kumar Mishra(Ph.D.) > > UGC-Dr. D. S. Kothari Post Doctoral Fellow > > Department of Chemical Sciences > > Tezpur University > > Tezpur- ASSAM > > INDIA > > > > > > From owner-chemistry@ccl.net Sun Aug 5 16:27:01 2012 From: "Amy J Austin docronindaemon(a)gmail.com" To: CCL Subject: CCL:G: Gaussian Message-Id: <-47325-120805135821-29728-DZy7fWpUYZqWZenO6Y27Kg : server.ccl.net> X-Original-From: "Amy J Austin" Date: Sun, 5 Aug 2012 13:58:18 -0400 Sent to CCL by: "Amy J Austin" [docronindaemon]=[gmail.com] Hello Elham, If you used the GammaOnly option (see link below), then the full k-integration isn't performed, only for k=0. http://www.gaussian.com/g_tech/g_ur/k_pbc.htm Best, Amy > "Elham Abdolhamidi flight.66.ab],[gmail.com" wrote: > > Sent to CCL by: "Elham Abdolhamidi" [flight.66.ab^_^gmail.com] > Dear Members; > I'm working with gaussian and when I calculate the energy levels of Polypyrrole(using PBC), for 10 levels (using 5/103=10) , I find the HOMO and LUMO in k=0,0,0 :-3.529 ev and -1.954 ev respectively. But when I find the energy levels in gamma point I find -15.863 ev and -9.8 ev for HOMO and LUMO. > I wanted to know why the energies in gamma point and in k=0,0,0 are not the same. > Regards. > >