Subject: Re: CCL:SUMMARY: One negative eigenvalue - No imaginary frequency!!??

From: Konstantin Kudin <konstantin_kudin..at..yahoo.com>
Date: Sat, 28 Aug 2004 10:22:50 -0700 (PDT)

--- Carlos Silva Lopez <csilval..at..uvigo.es> wrote:

> In a nutshell, I am even more clueless than before even though I have
> 
> received really nice and welcomed help from several netters. If
> nobody 
> has any further idea about what's going on here I will eventually 
> re-converge everything within a continuum dielectric method to see if
> it 
> counterbalances the anionic charge state and everything goes better.

 Carlos,

 There is not really anything out of ordinary in your particular case.
If you look at the output, you'll see 

Full mass-weighted force constant matrix:
 Low frequencies ---  -31.0607    0.0014    0.0024    0.0025   22.5484 

25.9445
 Low frequencies ---   42.3766   64.9775  107.1348
...
and normal coordinates:
                     1                      2                      3
                     A                      A                      A
 Frequencies --    18.6726                63.9044              
105.9740

 Full mass-weighted numbers (at the top) include 3 translations and 3
rotations. Once these 6 coordinates projected out, one gets numbers
that go under "Frequencies". While translational frequencies are
usually close to hard 0s (you see 3 of those in the top output),
rotational ones can be somewhere in the range -30 ... +30. This is
normal, no need to panic. Numerical DFT grids are not perfectly
rotationally invariant. 

 Lowest true vibrations will inevitably mix with some rotations, that
is why "42 65 107" became "19 64 106".

 In any event, such low lowest true frequencies indicate that the
molecule you're looking at has very "soft" normal modes. If you do not
like that, choose a better molecule!

 I hope that helps.

 Kostya

__________________________________
Do you Yahoo!?
Read only the mail you want - Yahoo! Mail SpamGuard.
http://promotions.yahoo.com/new_mail