Subject: QM study of heterogeneous reactions - 2

From: Dr Mark J Biggs <[email-masked]>
Date: Thu, 27 Apr 2000 08:59:44 +0100

Hi All!

have had two very helpful replies to my original question so far - many
thanks to these people.  Further comments are welcome.

I must make a correction to my original e-mail and would like to offer
more thoughts:

The O-down config in the paper I quoted was less stable than N-down - this
is why they used O-down.  However, this fact does not change the thrust of
my original question - I am trying to get to the bottem of why any given
start point is used in preference to another OR, more importantly, why we
should not consider possibilities as a function of: angle of approach as well
as orientation of molecule and temperature.

One of the responses I have got so far makes it clear that temperature can
be very important and that the O K path may be much in error.

Here are some more of my thoughts on this - I welcome all comments:

The standard approach taken in many papers appears to assume that one
can start from a single particular configuration and that only the
transition states of the various elementary steps leading away from that
point are important.  In a real system, molecules will approach from a
range of angles and with a range of orientations and with a given kinetic
energy, all of which will dictate the reaction path taken, if reaction
infact occurs at all.  Is it correct to say that QM as done in the paper
I cite (and others) cannot account for this situation and, therefore,
conclusions will never be definitive but, rather, always dependent
upon the initial assumed state?  If we had all the computer power we wanted,
would QM in the case be done differently? (e.g. do QM MD with lots of
molecules and active sites and let the system "react" and accumulate
staistics - i.e. much as we do in classical MD for transport properties).

Many thanks in advance.

Regards,

Mark