Subject: Hartree-Fock, Coulomb, Fermi

From: elewars <[email-masked]>
Date: Sun, 16 Jun 2002 18:00:07 -0400

2002 June 16

Hello,

The HF method gives "absolute" energies that are too high, because it
overestimates electron-electron repulsion. However, there are two kinds
of electron-electron repulsion: classical Coulomb (-->Coulomb hole),
arising from electric charge, and quantum mechanical or Fermi repulsion
(--> Fermi hole), which exists between electrons of like spin. The HF
approximate treatment of electron correlation  arises from the use of
just one determinant, and from the "smeared electron cloud" integration
used to get the J and K integrals.

Questions: (1) Is it now well-recognized which effect, Coulomb or Fermi,
causes the main problem with HF energies?  (2) Is there general
agreement on which approximation is worse, single-determinant or average
electron cloud (or maybe the two can't be disentangled)?

Thanks

E. Lewars
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