Are HartreeFock atoms too small or too large?
(2004) In Physical Chemistry Chemical Physics 6(11). p.29282931 Abstract
 We address the simple question, whether HartreeFock atoms are smaller or larger than exact (Schrodinger) atoms. As a measure, we use <r(2)>. We study the ground state of the atoms HeKr. The unrestricted HartreeFock 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 NNe, and Cl, Ar... (More)
 We address the simple question, whether HartreeFock atoms are smaller or larger than exact (Schrodinger) atoms. As a measure, we use <r(2)>. We study the ground state of the atoms HeKr. The unrestricted HartreeFock 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 NNe, 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:
http://lup.lub.lu.se/record/139637
 author
 Cohen, A J; Handy, N C and Roos, Björn ^{LU}
 organization
 publishing date
 2004
 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
 14639084
 DOI
 10.1039/b402989p
 language
 English
 LU publication?
 yes
 id
 5a9d0450d6464599ac47030a5f94dcda (old id 139637)
 date added to LUP
 20070717 09:09:46
 date last changed
 20180107 09:35:48
@article{5a9d0450d6464599ac47030a5f94dcda, abstract = {We address the simple question, whether HartreeFock atoms are smaller or larger than exact (Schrodinger) atoms. As a measure, we use <r(2)>. We study the ground state of the atoms HeKr. The unrestricted HartreeFock 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 NNe, 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 = {14639084}, language = {eng}, number = {11}, pages = {29282931}, publisher = {Royal Society of Chemistry}, series = {Physical Chemistry Chemical Physics}, title = {Are HartreeFock atoms too small or too large?}, url = {http://dx.doi.org/10.1039/b402989p}, volume = {6}, year = {2004}, }