[en] The generalized Koopmans theorem gives an estimate of the lowest ionization energy of an N-electron system. The approximate lowest ionization energy is obtained as the lowest eigenvalue of a generalized eigenvalue problem. It has been shown that the generalized Koopmans theorem predicts the exact lowest ionization energy for Coulomb systems. However, it has also been shown that in general no eigenvalue of the generalized Koopmans procedure corresponds to an exact ionization energy. This paradox is resolved by demonstrating that the lowest eigenvalue of the generalized Koopmans procedure does, in general, not exist for Coulomb systems. Nevertheless, it will also be shown that the generalized Koopmans approach gives ionization energies which are arbitrary close to the exact lowest ionization energy. The eigenvalues of the extended Koopmans theorem have an accumulation point given by the exact lowest ionization energy

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[en] Ionization potentials of chemical elements with the serial numbers 71-86 and 81-102 for some electrons of 0-level and P-level, respectively, are determined. The diagram of separation energy of K-, L-, M-, N-, O-, P-, Q- electrons of outer levels for all the elements of the D.I. Mendeleev periodic system is plotted

[en] The first ionization potential (IP_1) of element 103, lawrencium (Lr), has been successfully determined for the first time by using a newly developed method based on a surface ionization process. The measured IP_1 value is 4.963"0"."0"8_0_._0_7 eV. This value is the smallest among those of actinide elements and is in excellent agreement with the value of 4.963(15) eV predicted by state-of-the-art relativistic calculations also performed in this work. Our results strongly support that the Lr atom has an electronic configuration of [Rn]7s"25f"1"47p"1_1_/_2, which is influenced by strong relativistic effects. The present work provides a reliable benchmark for theoretical calculations and also opens the way for studies on atomic properties of heavy elements with atomic number Z > 100. Moreover, the present achievement has triggered a controversy on the position of lutetium (Lu) and Lr in the Periodic Table of Elements.

[en] Using beryllium as a model system it is suggested that cluster simulations of core-electron ionization potentials in metals should be carried out with the same number of electrons in the initial and final states

[en] Recently observed magic number data for Na_N clusters in the size range from 100 to 900 atoms cannot be fully explained by density functional calculations using a homogeneous, spherical positive charge background. However, a centrally compressed spherical background yields steps in the ionization potential at just those magic numbers observed experimentally. (orig.)

[en] A computational approach is presented for prediction and interpretation of core-level spectra of complex molecules. Applications are presented for several isolated organic molecules, sampling a range of chemical bonding and structural motifs. Comparison with gas phase measurements indicate that spectral lineshapes are accurately reproduced both above and below the ionization potential, without resort to ad hoc broadening. Agreement with experiment is significantly improved upon inclusion of vibrations via molecular dynamics sampling. We isolate and characterize spectral features due to particular electronic transitions enabled by vibrations, noting that even zero-point motion is sufficient in some cases

[en] The use of back-transformed pair natural orbitals in the calculation of excited state energies, ionization potentials, and electron affinities is investigated within the framework of equation of motion coupled cluster theory and its similarity transformed variant. Possible approaches to a more optimal use of pair natural orbitals in these methods are indicated.

[en] We report the first adiabatic ionization energy (I₁) of benzene, and the ortho, meta and para isomers of fluoro-, chloro- and bromobenzonitrile, extracted from gas-phase photoionization spectra measured up to the LiF cut-off. In every case, I₁ for the disubstituted benzene species is blue-shifted from I₁ in benzene. Moreover, I₁ decreases along the series F, Cl, Br. We explain these trends qualitatively by invoking destabilization/stabilization of the topmost filled πMO of benzene by donor/acceptor substituents. (orig.)

[en] A list of all relevant contributions, known to the authors, concerning the critical ionization velocity phenomena is presented. The contributions are classified and described in a few sentences. (Authors)