Advanced

Are Hartree-Fock atoms too small or too large?

Cohen, A J; Handy, N C and Roos, Björn LU (2004) In Physical Chemistry Chemical Physics 6(11). p.2928-2931
Abstract
We address the simple question, whether Hartree-Fock atoms are smaller or larger than exact (Schrodinger) atoms. As a measure, we use <r(2)>. We study the ground state of the atoms He-Kr. The unrestricted Hartree-Fock method is used. To obtain the Schrodinger values we use the finite field CASPT2 approach, and the full CI scheme where possible. CASSCF calculations are also reported. Very large basis sets are employed. We find that for those atoms for which the CASSCF wavefunction is distinct from the HF wavefunction, the Schrodinger values are distinctly smaller than the HF values. Most other atoms are also smaller than the HF values, (or the same within a numerical uncertainty), the exceptions being the hard atoms N-Ne, and Cl, Ar... (More)
We address the simple question, whether Hartree-Fock atoms are smaller or larger than exact (Schrodinger) atoms. As a measure, we use <r(2)>. We study the ground state of the atoms He-Kr. The unrestricted Hartree-Fock method is used. To obtain the Schrodinger values we use the finite field CASPT2 approach, and the full CI scheme where possible. CASSCF calculations are also reported. Very large basis sets are employed. We find that for those atoms for which the CASSCF wavefunction is distinct from the HF wavefunction, the Schrodinger values are distinctly smaller than the HF values. Most other atoms are also smaller than the HF values, (or the same within a numerical uncertainty), the exceptions being the hard atoms N-Ne, and Cl, Ar and Kr. We interpret our results in terms of categories of correlation contribution. It is also of interest to test the performance of density functional theory (DFT); we find on the whole that the predictions are good, with B3LYP giving close agreement with finite field CASPT2 for nearly all atoms, in particular for the transition metals. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Chemistry Chemical Physics
volume
6
issue
11
pages
2928 - 2931
publisher
Royal Society of Chemistry
external identifiers
  • wos:000222357600021
  • scopus:3042781273
ISSN
1463-9084
DOI
10.1039/b402989p
language
English
LU publication?
yes
id
5a9d0450-d646-4599-ac47-030a5f94dcda (old id 139637)
date added to LUP
2007-07-17 09:09:46
date last changed
2017-01-01 07:17:20
@article{5a9d0450-d646-4599-ac47-030a5f94dcda,
  abstract     = {We address the simple question, whether Hartree-Fock atoms are smaller or larger than exact (Schrodinger) atoms. As a measure, we use &lt;r(2)&gt;. We study the ground state of the atoms He-Kr. The unrestricted Hartree-Fock method is used. To obtain the Schrodinger values we use the finite field CASPT2 approach, and the full CI scheme where possible. CASSCF calculations are also reported. Very large basis sets are employed. We find that for those atoms for which the CASSCF wavefunction is distinct from the HF wavefunction, the Schrodinger values are distinctly smaller than the HF values. Most other atoms are also smaller than the HF values, (or the same within a numerical uncertainty), the exceptions being the hard atoms N-Ne, and Cl, Ar and Kr. We interpret our results in terms of categories of correlation contribution. It is also of interest to test the performance of density functional theory (DFT); we find on the whole that the predictions are good, with B3LYP giving close agreement with finite field CASPT2 for nearly all atoms, in particular for the transition metals.},
  author       = {Cohen, A J and Handy, N C and Roos, Björn},
  issn         = {1463-9084},
  language     = {eng},
  number       = {11},
  pages        = {2928--2931},
  publisher    = {Royal Society of Chemistry},
  series       = {Physical Chemistry Chemical Physics},
  title        = {Are Hartree-Fock atoms too small or too large?},
  url          = {http://dx.doi.org/10.1039/b402989p},
  volume       = {6},
  year         = {2004},
}