Summery:exact energy of atoms or small poly-atoms

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 <mnolan { *at * } nmrc.ucc.ie>:
 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 <elewars { *at * } trentu.ca>:
 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 <ida { *at * } ihpc.nus.edu.sg>:
        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 <dilys98 { *at * } mails.tsinghua.edu.cn>
 aug-cc-pv6z
 Frank Jensen <frj { *at * } dou.dk>:
 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" <lbbg123 { *at * } etang.com>
 To: "CCL" <chemistry { *at * } ccl.net>
 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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