Re: CCL:Q:warning in G03 frequency output

 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