| Autor: |
Allen, Mark J., Tozer, David J. |
| Předmět: |
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| Zdroj: |
Molecular Physics; 2/20/2002, Vol. 100 Issue 4, p433-439, 7p |
| Abstrakt: |
Kohn-Sham eigenvalues are determined from coupled cluster electron densities. The calculated HOMO-LUMO eigenvalue differences are compared with those from conventional generalized gradient approximation (GGA) exchange-correlation functionals for a range of small molecules. In all cases, GGA HOMO-LUMO differences are smaller than those calculated from the coupled cluster densities. When the GGA HOMO-LUMO differences are explicitly corrected - such that they equal those calculated from electron densities - significant improvements in NMR shielding constants are obtained. The eigenvalues calculated from electron densities are also used to approximate the magnitude of the integer discontinuity in the exact exchange-correlation potential. The value of the Kohn-Sham HOMO eigenvalue is then considered. Although HOMO eigenvalues from high quality, asymptotically vanishing, exchange-correlation potentials are close to the negative of the ionization potential, HOMO eigenvalues from the GGA functionals are shifted upwards by approximately 50% of the calculated integer discontinuity. An alternative approach for correcting NMR shielding constants is investigated. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
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