Subject: Re: CCL:Q:warning in G03 frequency output

From: "CHEMPATH, SHAJI" <shaji[at]berkeley.edu>
Date: Mon, 29 Nov 2004 13:20:18 -0800

Hi Georgina,
that means you have ltos of frequencies (23 of them) which are very small
and harmonic approximation may not be valid 
you can read more about it  at the G03 web site white papers:
http://www.gaussian.com/g_whitepap/white_pap.htm

some of these modes correspond to rotational motion of ligands (like hindered rotation)

If you optimized using the tight criteria some of those low frequenices will go away.  For large 
molecules there will always be some low frequency modes..

Shaji

On Mon, 29 Nov 2004 16:06:01 +0000
  Georgina Aitken <g.d.c.aitken[at]sussex.ac.uk> wrote:
>Dear CCLers,
>
>I am a PhD student and have been getting the following warning messages in
>the thermochemistry section of my Gaussian frequency outputs for various divalent Pb-ligand 
>complexes:
>
>"Principal axes and moments of inertia in atomic units:
>                           1         2         3
>     EIGENVALUES --  4494.802316560.791727501.25369
>           X            0.99998   0.00350   0.00560
>           Y           -0.00289   0.99445  -0.10519
>           Z           -0.00593   0.10517   0.99444
> This molecule is an asymmetric top.
> Rotational symmetry number  1.
> Warning -- assumption of classical behavior for rotation
>           may cause significant error
> Rotational temperatures (Kelvin)      0.01927     0.01320     0.01155
> Rotational constants (GHZ):           0.40152     0.27508     0.24059
> Zero-point vibrational energy     647177.6 (Joules/Mol)
>                                  154.67917 (Kcal/Mol)
> Warning -- explicit consideration of  23 degrees of freedom as
>           vibrations may cause significant error "
>
>Does this mean that the zero point energy correction is not reliable? What
>can I do about it?
>
>Thanks in advance,
>
>Georgina Aitken
>
>
>
>
>
>
>
>
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--------------------------------------------
Shaji Chempath