The harmonic frequencies = are independent of the coordinates used for the analysis, but any finite di= splacement along the corresponding normal modes depends strongly on the coordinates used for the analysis. Essentially all standar= d programs use Cartesian coordinates, but these are usually poor for repres= enting the actual vibrational motion for a non-trivial displacement. Calcul= ating the energy along a Cartesian normal mode displacement is unlikely to give an accurate picture of the vi= brational potential along that normal mode. If you doubt that, try followin= g the Cartesian version of the normal mode describing the rotation around t= he C –C bond in ethane, and you will rapidly discover that it significantly alters the C-H bond distances = as well. Performing the vibrational analysis in e.g. internal coordinates w= ill give a much better representation for large displacements, but few prog= rams have that capability.

<= /p>

Frank

<= /p>

Frank Jensen
Assoc. Prof.
Dept. of Chemistry
Aarhus University
http://old.chem.au= .dk/~frj

<= /p>

From: owner-ch= emistry+frj=3D=3Dchem.au.dk!A!ccl.net [mailto:owner-chemistry+frj=3D= =3Dchem.au.dk!A!ccl.net] On Behalf Of Jens Spanget-Larsen spanget**ruc.dk
Sent: 17. april 2013 19:14
To: Frank Jensen
Subject: CCL:G: SV: CCL:G: Scanning potential energy along a normal = mode

Dear Devandra,

I do not think Gaussian has a procedure to do this. Some time ago = I performed analyses of the so-called bell-clapper vibrational mode of 1,6,= 6a-trithiapentalene by scanning along the normal coordinate. The energy was calculated for a series of points cor= responding to displacement of the nuclei along the coordinate. You can= find the results and some relationships in: Spanget-Larsen & Ande= rsen, PCCP 3, 908-16 (2001).

Jens >--<

------------------------------------------------------

JENS SPANGET-LARSEN &nbs= p; Office: +45 4674 2710

Dept. of Science (18.1) Fax: &= nbsp; +45 4674 3011

Roskilde University &nbs= p; Mobile: +45 2320 6246

P.O.Box 260 = E-Mail: &= nbsp; spanget++ruc.dk

DK-4000 Roskilde, Denmark http://www.ruc.dk/~spanget

------------------------------------------------------

Fra: owner-chemistry+spanget= =3D=3Druc.dk++ccl.net [owner-chemistry+spanget=3D=3Druc.dk++ccl.net] p=E5 vegne af D= evendra Mani devdmani10%a%gmail.com [owner-chemistry++ccl.net]
Sendt: 17. april 2013 15:32
Til: Jens Spanget-Larsen
Emne: CCL:G: Scanning potential energy along a normal mode

Dear CCLers, =

I want to s= can potential energy along a particular normal mode of vibration . Is there= anyway to do it using Gaussian or any other software ?

Any kind of suggestions would be highly appreciated.

Thanks,

Devendra