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Date: Thu, 13 Jul 1995 12:18:15 -0400
From: "E. Lewars" <elewars #at# alchemy.chem.utoronto.ca>
Message-Id: <199507131618.MAA12031 \\at// alchemy.chem.utoronto.ca>
To: chemistry \\at// ccl.net
Subject: 3-21G(*) BASIS


Re the recent query about the 3-21G(*) basis set:
This is discussed in the ab initio bible (Hehre, Radom, Schleyer, Pople)
pp 84-86; see also several of the Tables in this book.  On p 86: "...the 
3-21G(*) basis set should find considerable use as an alternative to
6-31G* as a means of providing structures and normal-mode frequencies that
closely approximate those of the larger basis representation."  In Hehre's
*Practical Strategies for Electronic Structure Calculations*, on e.g.
pp 54-69, it is shown that the 3-21G(*) basis gives relative energies
extraordinarily close tho those of the 6-31G* basis (look at compounds
with the Na--Cl elements, for which the * is relevant).
  maybe the point is not whether it's "unbalanced", but whether it works
(as far as d-orbital participation goes, Nature is unbalanced).
Errol Lewars
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