Subject: Summary: DFT on openshell-Systems

From: Frank Schaper <[email-masked]>
Date: Sun, 23 Jun 2002 19:21:45 +0200

Dear Netters,
thanx for the fast response to:
"Deng, Jun" <[email-masked]>,
"Per-Ola Norrby" <[email-masked]>,
Stefan Grimme <[email-masked]>,
Tomasz Borowski <[email-masked]>,
Sorana Ionescu <[email-masked]>,
Antonia de Noronha <noronha@dedalus>
and Frank Neese <[email-masked]>.

Here is requested summary:

- Is a strong dependence on the DFT-functional a "normal" behavior for
open-shell systems?

The answer was a general "yes" from all experts. Sometimes even orbital
orders differ with the chosen functional. The local density approximation
(VWN-functional) was regarded a bad choice anyway.  In general, DFT seems
to prefer lower spin states in contrast to HF-methods.

- Is there any way to take a shortcut for geometry optimizations? E.g.
calculating the geometry closed-shell and using single-point energies for
different open-shell spin states.

- Is a geometry optimization mandatory for every spin state (possible in
my case S=1, 3 and 5) or are single-point calculations sufficient? I'm
very much afraid they are not.

Summarizing the answers to both questions, it seems to be necessary to
optimize every geometry with the functional used for the energy
calculations. Geometries should also be optimized for every spin state
(that was a silly question in any case).

- Can the calculated energies of the same complex with different spin
states be compared directly or is the spin-pairing-energy missing to some
extend?

Here the opinions seem to differ a little bit. As far as I have
understood, energies of different spin states can be compared, i.e. the
spin pairing energy is included in the calculated energies.  On the other
hand, single-determinant DFT-methods seem to have problems describing
lower spin states and the relative energies (though they can be compared
in principle) are rather qualitative up to wrong. Multi-configuration
methods were proposed to give better results.

Thanks again for the responses.

Hein

-- 
Frank (Hein) Schaper - AG Brintzinger - Universitaet Konstanz

email : [email-masked] - [email-masked]
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