# The exactness of the extended Koopmansâ€™ theorem: A numerical study

## Related Articles

- Finite-element multiconfiguration Hartreeâ€“Fock calculations on the excitation energies and the ionization potential of oxygen. Sundholm, Dage; Olsen, Jeppe; Alexander, S. A. // Journal of Chemical Physics;4/1/1992, Vol. 96 Issue 7, p5229
The 3P, 1D, and 1S states of oxygen and the 4S ground state of the oxygen cation have been studied using large numerical multiconfiguration Hartreeâ€“Fock calculations with systematically increased active spaces. The nonrelativistic valence limits for the excitation energies are 1.968 and...

- Ab initio calculations on electronic states of Be13. Ermler, W. C.; Kern, C. W.; Pitzer, R. M.; Winter, N. W. // Journal of Chemical Physics;4/1/1986, Vol. 84 Issue 7, p3937
A cluster of 13 beryllium atoms has been studied in ab initio Hartreeâ€“Fock calculations. The chosen geometric configuration has D3h symmetry and corresponds to a central Be with 12 atoms situated at the hexagonal close-packed, nearest-neighbor positions. The lowest energy electronic state...

- Calculation and interpretation of total energies in electron propagator theory. Ortiz, J. V. // Journal of Chemical Physics;10/1/1995, Vol. 103 Issue 13, p5630
Ground state total energies and one-electron density matrices can be calculated from contour integrals over the electron propagator. Ionization energies and corresponding Feynmanâ€“Dyson amplitudes are related simply to ground state properties. Total energy formulas derived from electron...

- Comparison between molecular orbital and surface integral calculations of the exchange energy for the homonuclear dimer ions He+2, Li+2, and Be+2. Chang, T. C.; Tang, K. T. // Journal of Chemical Physics;12/22/1995, Vol. 103 Issue 24, p10580
The exchange energy, defined as half of the energy splitting of the gerade and ungerade states of a molecular ion, is investigated by molecular orbital calculations and by the surface integral method. Numerical results of He+2, Li+2, and Be+2 are obtained through restricted Hartreeâ€“Fock,...

- Radial behavior of the average local ionization energies of atoms. Politzer, Peter; Murray, Jane S.; Grice, M. Edward; Brinck, Tore; Ranganathan, Shoba // Journal of Chemical Physics;11/1/1991, Vol. 95 Issue 9, p6699
The radial behavior of the average local ionization energy I(r) has been investigated for the atoms Heâ€“Kr, using ab initio Hartreeâ€“Fock atomic wave functions. I(r) is found to decrease in a stepwise manner with the inflection points serving effectively to define boundaries between...

- A linear combination of Gaussian-type orbitals (LCGTO) XÎ± study of ferrocene: The metal-to-ring distance and ionization potentials. Rösch, N.; Jörg, H. // Journal of Chemical Physics;5/15/1986, Vol. 84 Issue 10, p5967
The metal-to-ring distance of ferrocene, Fe(C5H5)2, has been optimized using the LCGTO-XÎ± method. The resulting distance is 0.047 Ã… shorter than the experimental value of 1.65 Ã…. The corresponding symmetric stretching frequency of 331 cm-1 shows good agreement with experiment (303...

- Relativistic effects on sixth group monohydrides. Pisani, L.; Clementi, E. // Journal of Chemical Physics;12/1/1995, Vol. 103 Issue 21, p9321
Diracâ€“Fock and Hartreeâ€“Fock calculations have been performed for the ground state of the HO, HS, HSe, HTe, and HPo molecules. Equilibrium geometries, atomization energies, and ionization potentials, with both methods, are evaluated, compared, and discussed. Calculations on the...

- Exact ionization potentials from wavefunction asymptotics: The extended Koopmansâ€™ theorem, revisited. Vanfleteren, Diederik; Van Neck, Dimitri; Ayers, Paul W.; Morrison, Robert C.; Bultinck, Patrick // Journal of Chemical Physics;5/21/2009, Vol. 130 Issue 19, p194104
A simple explanation is given for the exactness of the extended Koopmansâ€™ theorem, (EKT) for computing the removal energy of any many-electron system to the lowest-energy ground state ion of a given symmetry. In particular, by removing the electron from a â€œremoval orbitalâ€ of...

- Stability of MX2-3 ions in the gas phase and when do ionic molecules have large ionization potentials. Scheller, M. K.; Cederbaum, L. S. // Journal of Chemical Physics;7/1/1993, Vol. 99 Issue 1, p441
The present work aims at theoretical consideration of the geometrical and electronic structures of a homologous series of free MXmq--type alkali halides (M=Li, Na, K; X=F, Cl; m=1,2,3; q=0,1,2) in order to get insight into their kinetic and electronic stability. At the ab initio...