TRANSITION STATE LOCATION

[Andy Holder <AHOLDER \\at// VAX1.UMKC.EDU>]

On the subject of transition states, ONE negative frequency indicates
   a transition state.  (Since the frequencies are computed directly
   from the force constants, it is not neccessary to check them as well.)
   If you have more than one, a true transition state has not been
   reached.  If there are two, you are on a "ridgeline".  You must
   analyze the motion of the smaller value and "goose" the geometry
   along this motion and re-optimize.  (Yes, I know, incredibly ted-
   ious.)  Very small negative frequencies usually correspond to
   things like methyl rotations.  I don't know the exact structure you
   are working with, but that is likely.
 If you have more than two negative frequencies, this can be a problem.
   People doing reactions spend the majority  of their time stomping
   out spurious negative frequencies.  As if that wasn't enough, you
   must make sure that your TS corresponds to the one for the reaction
   you are examining.  To do this, examine the motions associated with
   the ONE negative frequency and again "goose" the geometry along
   these coordinates.  If you end up with product, that's good.  You
   can also goose it backwards and hopefully end up with reactant.
 I have mentioned twice "analyze the motion".  You can do this is
   several ways.  After doing a FORCE calculation, the cartesian
   components of motion for each atom are printed under the force
   constant listing.  Making sure that the molecule is oriented the
   way the force calculation has indicated (its in there) just look
   at what the atoms with large components actually do for a partic-
   ular vibration.  The second method (the one I use) is to perform
   an LTRD calculation.  This will give you the components of nega-
   tive frequencies in internal coordinates.  This is usually much
   easier to interpret.  Again figure out which components are large
   and count optimizable geometric parameters to match them up.
 Hope this abbreviated version helps.
    Andy Holder
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                               DR. ANDREW HOLDER
              Assistant Professor of Computational/Organic Chemistry
 Department of Chemistry              ||  BITNET Addr:   AHOLDER \\at// UMKCVAX1
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