From owner-chemistry@ccl.net Thu Mar 5 11:11:00 2009 From: "Farhan Pasha pashafa(-)yahoo.co.in" To: CCL Subject: CCL:G: IRC calculation Message-Id: <-38758-090304201638-19433-AJAakw+wBsa54VUjlc9XyA%%server.ccl.net> X-Original-From: Farhan Pasha Content-Type: multipart/alternative; boundary="0-1957794508-1236212180=:91046" Date: Thu, 5 Mar 2009 05:46:20 +0530 (IST) MIME-Version: 1.0 Sent to CCL by: Farhan Pasha [pashafa(!)yahoo.co.in] --0-1957794508-1236212180=:91046 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable hi =A0 If you using gaussian=A0 just do two seprate calculation using following ke= yword irc=3D(rcfc,forward) irc=3D(rcfc,reverse) it will work =A0 cheers pasha Correspondence Address Dr. Syed Farhan Ahmad Pasha Room No. 5202 Institut de Biologie Structurale Laboratoire de Dynamique Moleculaire 41 rue Jules Horowitz 38027 Grenoble cedex France tel : =0A=0A=0A Connect with friends all over the world. Get Yahoo! In= dia Messenger at http://in.messenger.yahoo.com/?wm=3Dn/ --0-1957794508-1236212180=:91046 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: quoted-printable
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hi
 
If you using gaussian  just do two seprate calculation using foll= owing keyword
irc=3D(rcfc,forward)
irc=3D(rcfc,reverse)
it will work
 
cheers
pasha


Correspondence Address
Dr. Syed Farhan Ahmad PashaRoom No. 5202
Institut de Biologie Structurale
Laboratoire de Dynam= ique Moleculaire
41 rue Jules Horowitz
38027 Grenoble cedex
France=
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www.ibs.fr

--- On We= d, 4/3/09, Sriraj Srinivasan ss537%a%drexel.edu <owner-chemistry/./ccl.= net> wrote:

From: Sriraj Srinivasan ss537%a%drexel.edu <ow= ner-chemistry/./ccl.net>
Subject: CCL:G: IRC calculation
To: "Pasha,= Frahan Ahmad " <pashafa/./yahoo.co.in>
Date: Wednesday, 4 M= arch, 2009, 10:10 PM


-----Inline Attachment Follows-----


Sent to CCL by: Sriraj Srinivasan [ss537:_:drexe= l.edu]

Hi Kavitha,

Make sure that your hessian is correct eno= ugh to go in both directions. This is critical for an IRC calculation to su= cceed. I do DFT calculations and have found no problems as such.

Sri= raj



----- Original Message -----
> From: "Justin Finne= rty justin.finnerty~~uni-oldenburg.de" <owner-chemistry/./ccl.net>
Date: Wednesday, Marc= h 4, 2009 8:12 am
Subject: CCL:G: IRC calculation

>
> S= ent to CCL by: Justin Finnerty [justin.finnerty*_*uni-oldenburg.de]
>=
> On Tue, 2009-03-03 at 09:48 -0500, Kavitha Velappan
> kavit= ha.velappan(a)gmail.com wrote:
> > Sent to CCL by: "Kavitha  = Velappan" [kavitha.velappan_-_gmail.com]
> > Hi all,
> >
> > I tried to do IRC calculation to follow the reaction path fo= r
> conformer interconversion (Dimethoxymethane G+G- to G-G- conform= er
> - rotation around OCH3 bond). The route section looks like this= :
> >
> > #N RB3LYP/6-31++G** IRC=3D(CalcFC,maxpoints=3D= 12)
>
> I have had this issue whenever I do an IRC with DFT in= gaussian.  The
> problems are as you see, the IRC only goes in = one direction and
> doesn'treach maxpoints.
>
> I found= that the best solution to this is to reduce the STEPSIZE. The
> defa= ult is 10 and I have had much success with STEPSIZE=3D4 or 3.  (You> have to increase MAXPOINTS accordingly!)  Using this I have
= > successfullyused IRC to go from the TS to close to the ground
>= state.  Using a small
> stepsize will increase the length of th= e calculation but not as
> much as
> it first appears because the previous step of the IRC is now much
> closerto the new step so= each step converges in two or three cycles.
>
> The other iss= ue is getting both the forward and reverse directions to
> work. I ha= ve found no reliable way to do this automatically in
> gaussianusing= DFT - gaussian always seems to go in one direction!
> My normal
= > solution is to manually modify the TS structure in the direction
&g= t; gaussian didn't go and start the IRC from the modified structure.  =
> How I
> modify the structure is of course based on the motio= n vectors of the
> imaginary frequency.
>
> PS Your inpu= t uses CALCFC, surely you could use READFC from the freq
> calculatio= n for the TS?
>
> Cheers
>     Justin
= >
> --
> Dr Justin Finnerty
> Rm W3-1-165  &nbs= p;      Ph  49&n= bsp;(441) 798 3726 
> = Carl von Ossietzky Universit=E4t Oldenburg
>
>
>
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