An average fock operator technique of approximate open-shell LCAO-MO-SCF calculation |
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Authors: | Sankar Prasad Bhattachararyya and Mihir Chowdhury |
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Institution: | (1) Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, 700 032 Calcutta, India |
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Abstract: | The exchange part of the usual Hartree-Fock potential in the unrestricted Hartree-Fock (UHF) theory is suitablyaveraged to construct an, average one-electron model Hamiltonian which generates a set of spin-restricted one-electron orbitals in
a self-consistent manner. These orbitals are then used to calculate the electronic energy of the open-shell system by using
the proper functional form for the energy which handles the exchange terms correctly. The eigenvalues ofF
av can be used for calculating either the spin-polarised or spin-averaged ionisation potentials of different orbitals at theKoopmans’ theorem level of approximation. Comparison ofE
ac with the UHF-energy shows thatE
UHF<E
ac in each case revealing some kind of an upper bound nature ofE
ac. An approximate variational argument is given. Relationship of our model with the hyper-Hartree-Fock theory of slater is
explored and the general problem of eliminating ‘self-interaction’ terms in average Fock-operator based theories is discussed. |
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Keywords: | Average Fock operator approximate open-shell theories half-electron method hyper-Hartree Fock model etc |
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