Dear All,

Georg Schreckenbach wrote:
> from the manual and from the respective publications, I understand that
> one should not use the non-relativistic basis sets for ZORA
> calculations.
> However, I am less clear about the reverse: Are there any
> fundamental or practical arguments against using ZORA basis sets for
> non-relativistic calculations? Does it make sense to do so? - I am
> asking because I want to calculate the magnitude of the 'relativistic
> contributions' to some properties. This would require using the exact
> same conditions, including the exact same basis sets, in the
> non-relativistic and relativistic cases.
Answer:
The all electron basis sets can be used both in
ZORA and in non-relativistic calculations.
In the frozen core basis sets the core orbitals are described
either non-relativistically or ZORA, thus one should use
the frozen core basis sets only where they were designed for.

The all-electron basis sets for ZORA, especially for Z>36 contain
extra compact STOs, which are needed for
a proper description of the relativistic orbitals.
In non-relativistic calculations these extra compact STOs will do no harm,
but they are not very useful.

Conclusion: It makes sense to do non-relativistic calculations
with all electron ZORA basis sets.
One should be more careful with ZORA calculations
with non-relativistic all electron basis sets for heavier atoms
(typical Z>36), since these non-relativistic basis sets
do not contain very compact STOs (steep functions), which are
very important in a relativistic calculation.
Most of the relativistic effect comes from the core region,
for example it effects the core wiggles of valence electrons.

Best regards,
Erik van Lenthe

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Dr. Erik van Lenthe SCIENTIFIC COMPUTING & MODELLING NV
Tel: +31 20 44 47615 Vrije Universiteit, Theoretische Chemie
secretary: 44 47519 De Boelelaan 1083
 fax: 44 47629 1081 HV Amsterdam, The Netherlands
 e-mail: vanlenthe@scm.com http://www.scm.com
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Received on 2002-07-31 13:25:38