3-21G(*) BASIS

["E. Lewars" <elewars |-at-| alchemy.chem.utoronto.ca>]

 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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