CCL:re DFT and small basis sets
- From: Tanja van Mourik <t.vanmourik.-at-.ucl.ac.uk>
- Subject: CCL:re DFT and small basis sets
- Date: Thu, 3 Jul 2003 11:58:23 +0100 (BST)
Lynch, Zhao and Truhlar advocate including diffuse functions on
non-hydrogenic atoms when calculating reaction energies, barrier
heights and conformational energies with DFT, see:
J Phys Chem A 107 (9): 1384-1388 (2003).
So I would recommend using 6-31+G* rather than 6-31G* as the smallest
basis set for yielding accurate results.
Tanja van Mourik
Royal Society University Research Fellow
University College London phone: +44 (0)20-7679-4663
20 Gordon Street e-mail: work: T.vanMourik.-at-.ucl.ac.uk
London WC1H 0AJ, UK home: tanja_van_mourik.-at-.btopenworld.com
> Re "Has anyone ever published a discussion of the accuracy of DFT at
> small basis sets?"
> I'm not sure just what you consider small (most workers now would likely
> say that
> 6-31G* is small), but DFT calculations are known to be saturated by
> functions more quickly than are ab initio calculations. Here are three
> 1) "Once the double split-valence level is reached, further
> in basis
> set quality offers little in the way of structutal or energetic
> improvement." G.
> N. Merrill, S. Gronert, and S. R. Kass. J Phys Chem, 1997, _101_, 204.
> 2) "Our results also show that B3LYP calculations converge rapidly
> increasing basis set size and that the cost-to-benefit- ratio is optimal
> at the
> 6-31G* basis set level. 6-31G* will be the basis set of choice in B3LYP
> calculations on much larger molecules [than C4H6O2]." P. J. Stephens,
> Devlin, C. F. Chablowski, and M. J. Frisch, J Phys Chem, 1994, _98_,
> 11623, and
> refs therein.
> 3) In defiance of tradition, the unequivocally small 3-21G(*) set has
> been used
> to optimize carbene geometries: H. M. Muchall, N. H. Werstiuk, and B.
> Can J Chem, 1998, _76_, 221.
> (You my also find some useful info in E. Lewars, "Computational
> Kluwer, 2003; section 188.8.131.52).
> E. Lewars
> Ed Brothers wrote:
> > Folks:
> > Has anyone ever published a discussion of the accuracy of DFT at
> > small basis sets?
> > Ed.
> > Merz group.
> > Penn State.
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