Subject: Gauche effect ab initio calculations

From: [email-masked] (M. Nicklaus)
Date: Tue, 31 May 94 20:04:00 -0400

Dear Net-Workers,

We are thinking about doing ab initio modeling (using Gaussian 92)
on small organic molecules which possess, apart from C, H, N, O,
a sulfur and a halogen atom (F, Cl, Br, I) in such an arrangement
that we expect interactions of the gauche-effect type to occur
between them.
   We would like to ask the experts what level of theory, basis
sets, electron correlation methods etc. they would recommend for
obtaining reliable conformational energies when calculating
local energy minima for such compounds.  Would different approaches
be advisable for geometry optimization vs. the final energy
calculation?  Would using non-standard basis sets (which ones? 
obtainable where?) be necessary especially for the higher-period 
halogens?
   Please answer to me directly.  I will summarize for the list
if I get useful replies.

   Thanks in advance,

   Marc

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 Marc C. Nicklaus                        Lab. of Medicinal Chemistry
 e-mail: [email-masked]               National Cancer Institute, NIH
 Phone:  (301) 402-3111                  Bldg 37, Rm 5B29
 Fax:    (301) 496-5839                  Bethesda, MD 20892
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