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SUMMARY:Are Hartree–Fock atoms too small or too large? - Priyanka Seth (
 TCM)
DTSTART:20100507T143000Z
DTEND:20100507T150000Z
UID:TALK24566@talks.cam.ac.uk
CONTACT:Daniel Cole
DESCRIPTION:"Aron J Cohen\, Nicholas C Handy and Bjorn O Roos\, Phys. Chem
 . Chem. Phys.\, 6\, 2928 (2004) ":http://www.rsc.org/Publishing/Journals/C
 P/article.asp?doi=b402989p\n\nWe address the simple question\, whether Har
 tree–Fock atoms are smaller or larger than exact (Schrödinger) atoms. A
 s a measure\, we use r2. We study the ground state of the atoms He–Kr. T
 he unrestricted Hartree–Fock method is used. To obtain the Schrödinger 
 values we use the finite field CASPT2 approach\, and the full CI scheme wh
 ere possible. CASSCF calculations are also reported. Very large basis sets
  are employed. We find that for those atoms for which the CASSCF wavefunct
 ion is distinct from the HF wavefunction\, the Schrödinger values are dis
 tinctly smaller than the HF values. Most other atoms are also smaller than
  the HF values\, (or the same within a numerical uncertainty)\, the except
 ions being the hard atoms N–Ne\, and Cl\, Ar and Kr. We interpret our re
 sults in terms of categories of correlation contribution. It is also of in
 terest to test the performance of density functional theory (DFT)\; we fin
 d on the whole that the predictions are good\, with B3LYP giving close agr
 eement with finite field CASPT2 for nearly all atoms\, in particular for t
 he transition metals.
LOCATION:TCM Seminar Room\, Cavendish Laboratory
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