Subject: so effects on geometry (was: high-quality GAMESS-US basis set for iodine?)

From: [email-masked] (Georg Schreckenbach)
Date: Mon, 3 Jan 2000 11:34:30 -0600

Dear Valentin and CCL,

>Does anybody know appropriate references on what effect: scalar-
>relativistic or spin-orbit has more effect on geometry?

There is one paper out by van Lenthe et al. where they compared scalar and
spin-orbit effects on the geometry and other properties of small molecules.
For instance, for I2, they find a difference in bond length of 0.019 Angstrom,
one of the largest for the set of molecules considered. So, the conclusion
was that the influence of spin-orbit effects on the geometry of closed-
shell molecules is modest only. The same is not true, of course, for other
properties including energetics or NMR. The reference is JCP 1996, 105, 6505.

   Besides, it is clear that one needs scalar relativistic effects to get the
geometries right, cf., e.g., the classic 1988 Chem Rev. review by Pyykkö. This,
then, is a point in favor of ECP basis sets for something as heavy as iodine :-)

>In most cases using ECP usually gives better agreement in geometry
>compared to all-electron calculations for iodine containing molecules.
>For example, one may take a look at recent publications with Stuttgart
>ECP basis set on iodine.

Best regards, Georg

--
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Dr. Georg Schreckenbach           Tel:     (USA)-505-667 7605
Theoretical Chemistry T-12        FAX:     (USA)-505-665 3909
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Laboratory, Los Alamos, New Mexico, 87545, USA
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