Subject: basis set balance?

From: [email-masked] (Douglas A. Smith Ph.D.)
Date: Mon, 27 Jan 1997 08:47:25 -0500

In the spirit of Jan's recent request for more teaching, I wholeheartedly
agree!  So, I have a need to learn something, and perhaps replies can be
sent directly to the list, not to me, so as to foster interactive
conversation (not enough of that anymore, it seems, appears here).

The question:  Can people please explain the concept of having a balanced
basis set and the dangers inherent in an unbalanced set?  In particular, why
can I not simply use a large basis, including extra split valance functions,
polarization and diffuse functions, only on the atoms I need them on, and a
smaller, more compact basis set on the "unimportant" atoms to my chemical
question?  This would certainly save time and resources during the calculation.

Doug
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