Subject: Reaction Paths ??

From: <[email-masked]>
Date: Tue, 10 Oct 1995 13:43:41 -0400 (EDT)

CCL Users:
  I would like to use MOPAC to investigate the reaction of H2 with a
planar molecule.  Since one is allowed just one reaction coordinate,
I set up the problem as follows:
 
  XX
  XX  2.5 -1  0.0              1
  H   .5  1  90.0  1  0.0 0    2  1
  H   .5  1  90.0  1  180.0  0 2  1  3
   etc.
 
  The planar molecule is fastened to the first dummy atom.  My idea
was to shorten the distances between to the two dummy atoms to study
the reaction.  My output is very strange.  The H2 hardly moves.  Each
cycle of the reaction shows the shortened distance I've selected, but
the xyz coordinates show the H2 out at approximately the 2.5 A starting
distance.
  Does anyone have any hints on how to vary this approach distance
properly?  Can one indeed use dummy atoms in a reaction path?  If so
then what is wrong?
  Regards, Dave Close.