[molpro-user] conical optimisation question
yfpjaya at gmail.com
Wed Jan 6 10:20:39 GMT 2010
I am working on minimising the energy of methoxy molecule (CH3O) with
respect to symmetric displacements that will preserve the C3v symmetry of
the molecule. In other words, I am using the active variables- CO bond
length, 3CH bonds displacements (all in same direction) and 3 HCO bending
displacements (all in same direction as in umbrella motion). As you will see
in the output of the following input, the final geometry after optimisation
is CO ~ 1.427 A, and corresponding parameters for CH and HCO angle.
I notice that when I scan the potential with respect to only CO bond
compression, the energy of the molecule when CO ~ 1.38 A for example is
lower than CO ~ 1.427 A. The CO bond compression preserves the C3v symmetry
of the molecule, and so I would expect the Conical optimisation procedure to
arrive at a minimum with respect to symmetric motions in the molecule. The
difference in energy between 2 above such geometries is about 100cm-1. How
can I force MOLPRO to search for the correct minimum with respect to the
symmetric motions? (I know that the asymmetric motions do not have a minimum
at C3v symmetry, hence the Jahn-Teller effect in the molecule.) I notice the
same trend with the other 2 symmetric motions as well. Any comments or
suggestions would be great.
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