CCL:G: IRC calculation

Sent to CCL by: Sriraj Srinivasan [ss537:_:drexel.edu]

Hi Kavitha,

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

Sriraj

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

>
> Sent to CCL by: Justin Finnerty [justin.finnerty*_*uni-oldenburg.de]
>
> On Tue, 2009-03-03 at 09:48 -0500, Kavitha Velappan
> kavitha.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 for
> conformer interconversion (Dimethoxymethane G+G- to G-G- conformer
> - rotation around OCH3 bond). The route section looks like this:
> >
> > #N RB3LYP/6-31++G** IRC=(CalcFC,maxpoints=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
> default is 10 and I have had much success with STEPSIZE=4 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 the 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 issue is getting both the forward and reverse directions to
> work. I have 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
> gaussian didn't go and start the IRC from the modified structure.
> How I
> modify the structure is of course based on the motion vectors of the
> imaginary frequency.
>
> PS Your input uses CALCFC, surely you could use READFC from the freq
> calculation for the TS?
>
> Cheers
> Justin
>
> --
> Dr Justin Finnerty
> Rm W3-1-165 Ph https://toolbaricons.s4benterprises.com/IEPlugin/inactive_a.compat.flex.w16.gif)" skypeid="1" skypeaction="drop" skypesms="0">https://toolbaricons.s4benterprises.com/IEPlugin/famfamfam/DE.gif)"> 49 (441) 798 3726
> Carl von Ossietzky Universität Oldenburg
>
>
>
> -= This is automatically added to each message by the mailing
> script =-
> To recover the email address of the author of the message, please
> changethe strange characters on the top line to the /./ sign. You
> can also
>
>
> E-mail to subscribers: CHEMISTRY/./ccl.net or use:
> http://www.ccl.net/cgi-bin/ccl/send_ccl_message
>
> E-mail to administrators: CHEMISTRY-REQUEST/./ccl.net or use
> http://www.ccl.net/cgi-bin/ccl/send_ccl_message
>
> Subscribe/Unsubscribe:
> http://www.ccl.net/chemistry/sub_unsub.shtml
>
> Before posting, check wait time at: http://www.ccl.net/" target=_blank>http://www.ccl.net
>
> Job: http://www.ccl.net/jobs
> Conferences:
> http://server.ccl.net/chemistry/announcements/conferences/
> Search Messages: http://www.ccl.net/chemistry/searchccl/index.shtml" target=_blank>http://www.ccl.net/chemistry/searchccl/index.shtml
>
> =
> http://www.ccl.net/spammers.txt
>
> RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/
>
>
>

-= This is automatically added to each message by the mailing script =-
To recover the email address of the author of the message, please change
the strange characters on the top line to the /./ sign. You can also
look up the X-Original-From: line in the mail header.

E-mail to subscribers: CHEMISTRY/./ccl.net or use:
http://www.ccl.net/cgi-bin/ccl/send_ccl_message

E-mail to administrators: CHEMISTRY-REQUEST/./ccl.net or use
http://www.ccl.net/cgi-bin/ccl/send_ccl_message

Subscribe/Unsubscribe:
http://www.ccl.net/chemistry/sub_unsub.shtml" target=_blank>http://www.ccl.net/chemistry/sub_unsub.shtml

Before posting, check wait time at: http://www.ccl.net

Job: http://www.ccl.net/jobs
Conferences: http://server.ccl.net/chemistry/announcements/conferences/

Search Messages: http://www.ccl.net/chemistry/searchccl/index.shtml
http://www.ccl.net/spammers.txt

RTFI: http://www.ccl.net/chemistry/aboutccl/instructions/