Subject: Summary:Shielding tensors for H

From: [email-masked] (Grzegorz Bakalarski)
Date: Mon, 14 Oct 96 09:07:31 +0100

Dear CCL Members,

On Monday I asked a question about NMR shielding tensors for
H atoms. It's hard to say but I've got only 2 (two) comments and
few qurries to summarize. It seems that there is no comparative study
 about calculating shielding tensors for H atom. Thus DO EXIST
publications on ^{11}B, ^{13}C, ^{15}N, ^{17}O, ^{19}F, ^{31}P ....
Some people have calculated ^{1}H shielding tensors for few molecules
but there was no systematic study on level of theory needed or basis set
effects. It really puzzles me ... .
For those  who asked here is reference to work by Cheeseman et al:

Cheeseman J.R., Trucks G.W., Keith T.A., Frisch M.J., J. Chem. Phys.
Vol 104, No. 14 (8 April 1996) pp. 5497-5509.

Thanks to Georg Schreckenbach and David E. Bernholdt who have shared their
thoughts.

Best regards,

Grzegorz Bakalarski
ICM|Warsaw University
POLAND
[email-masked]

==================  SUMMARY  ==================================

----------------- Q U E R R Y ------------------------------------

 Dear Netters,

Recently I've read article by Cheeseman el al. about calculating  absolute
and relative NMR shielding tensors from different level of theory ( HF, MP2 and
DFT) for different basis sets. The article is very interesting but the auhtors
deal only with more "difficult  cases - C, N and B atoms". I am interested
in  predicting NMR shielding tensors for H atoms in molecules ( it seems
a easier case). Could anyone point me to similar article where I could find
a systematic study of predicting NMR shielding tensors for H atom and it
dependency on level of theory and  basis set ? Any comments are also most 
welcomed!
Best regards,
  
------------------ R E P L I E S ----------------------------------------

>From [email-masked]

Hi Grzegorz,
I am always interested in the NMR stuff, therefore, I would be
interested in your summary. Further, would you mind providing me with
the reference for the article that you cite?

I am not sure why H should be less difficult then C,N or B. In fact,
I recall a presentation given recently by Don Chesnut where the conclusion
was that H is MORE difficult than, e.g., Carbon. It depends, of course,
on the meaning of "difficult". What Chesnut means is that the errors
in calculated 1H shieldings (or shifts) are bigger than for say Carbon,
if you consider the relative error w.r.t. the total shift range for
the given nucleus. Chesnut has written a number of very readable reviews
on NMR calculations, the most recent ones in "Reviews of Computational
Chemistry" (I am not sure here) and in "Annual Reports on NMR Spectroscopy"
Vol.29, G.A.Webb (Ed.), Academic Press, New York, 1994. I am not
sure though whether your particular question is covered there.

Yours, Georg
----------------

From: [email-masked]

My experience (not yet published) is that H shieldings are harder to
get right (absolute, not sure about relative).  I don't understand
why this is; neither does an experimental colleague with extensive
computational experience with shieldings.  Part of it has to do with
the small range and shifts typical for H, but I don't think that's the
whole story.
--
David E. Bernholdt                      | Email:  [email-masked]
______________________

D. Y. Chen and Ray Crawford asked for summary.

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