Subject: Summery:exact energy of atoms or small poly-atoms

From: "Zhenhua Li" <[email-masked]>
Date: Sat, 13 Oct 2001 18:44:11 +0800

Thanks for everyone:
The information I obtained is that the HF limit or even CASSCF limit of
atoms and diatoms can be calculated by numerical HF codes available free of
charge. But it is rather difficult to obtain exact correlation energies.
Several groups are developing correlation methods explicitely including
correlation, i.e. inter-electron distances to calculate exact
non-relativistic correlation energy. Some literatures have estimated the
correlation energy of atoms by substracting experimental energies with
experimentally or theoretically determined relativistic energy and HF limit.
Thanks for all warm replies.

Zhenhua

Following is a summary of replies:

Michael Nolan <[email-masked]>:

there is a paper by Davidson et al, PRA 1991, vol 44, 7071,
in which they present exact energies for atoms and ions thereof
in the first row of the periodic table.
There might be newer papers, I am not sure.

elewars <[email-masked]>:

Hello,

I don't think there are exact solutions of the S. equation except for
one-electron atoms (H, He+, ...) or molecules (like H2+). There are ways to
extrapolate to the basis set limit, with various degrees of accuracy:
"complete
basis set" methods, CBS-4, CBS-Q, CBS-APNO (G. A. Petersson): see papers in
J.
Chem. Phys., book "Computational Thermochemistry", Edited by Irikura and
Frurip
(ACS, Washington DC, 1998).

Ngai Ling Ida Ma <[email-masked]>:

       Not sure whether this is what you are looking for.  Are you looking
for full-CI benchmarks?  If that is the case, you might like to check up on
N.C. Handy's paper.  He has a program for doing full-CI, and I remember he
has several papers in JCP between 1980-1990 of these systems.  I don't
think he has "everything" in one paper but it should give you a start.

Denny <[email-masked]>

aug-cc-pv6z

Frank Jensen <[email-masked]>:

HF limits for atoms are in the literature. HF
limits for some diatomic systems are also there, or can
be generated by numerical HF programs which are available
free of charge. In connection with other work I have developed
some basis sets which should be able to get 10^-7 accurcy
on absolute energies in a relative sense, and which can be
used for polyatomic molecules.
Absolute energies including electron correlation
are harder to come by. Check some of the recent work on
R12 methods for getting estimates for small molecules.
For atoms the sum of ionization potentials
give the total energy experimentally.

----- Original Message -----
From: "Zhenhua Li" <[email-masked]>
To: "CCL" <[email-masked]>
Sent: Monday, October 08, 2001 11:18 PM
Subject: CCL:exact energy of atoms or small poly-atoms

> Dear listers,
> Have you any idea how to find energies of exact or close to exact (either
> SCF or correlation level) one-particle basis set limit for atoms or small
> poly-atoms?
> Are there any exact energies of atoms or small poly-atoms (exact solution
of
> Schrodinger equation)?
>
> Li Zhenhua
>
>
>
>
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