Subject: HF and EC bond lengths

From: "Eugene G. Noda" <[email-masked]>
Date: Fri, 21 Nov 1997 12:24:37 +0200

At 06:35 PM 11/19/97 -0800, Jason Perry wrote:
>
>2)  HF is biased toward the metal s orbital over the metal d orbital.  The
>s orbital is more diffuse than the d orbitals and requires less correlation
>to describe properly.  You can test this by calculating the metal s2dn-2,
>s1dn-1, and dn state spittings of the metal.  You get much better agreement
>with experiment when correlation and good basis sets are used.  Otherwise,
>there is a bias in favor of the s2dn-2 and s1dn-1 states.  Because of this
>bias, HF descriptions of metal-ligand covalent bonds often have too much
>s character in them.  With the addition of correlation more d character
>is introduced into the bond.  Since the s orbital is larger than the d
>orbital, reducing s character and introducing more d character coincides 
>with a shortening of the bond.
>

Dear Jason

No one is against to discuss correlation shortening bonds in organometallics
using different methods. However, I am strongly against to involve so-called
"s-d mixing" argument. In my opinion, this is the case when poor computational
model leads to the bad physics. Take a look at Fig. 5 from my recent article
http://www.zsu.zaporizhzhe.ua/~noda/ccl_disc.html which I specially to the
present discussion placed on the web. Of course, some portion of s-p density
in the bonding region is really existed. However, my calcs show that this
density
comes from 3s and 3p orbitals at least for the first row transmetals. Even
if you
ignore this, I will be insisted that many decades speculations in the frame of
"mixing" were completely unfruitful and totally misleading. I tend to classify
such models as a plausible physics.

Sincerely, Eugene

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