title: Atomic and Molecular Complex Resonances from Real Eigenvalues Using Standard (Hermitian) Electronic Structure Calculations.
abstract: Complex eigenvalues, resonances, play an important role in a large variety of fields in physics and chemistry. For example, in cold molecular collision experiments and electron scattering experiments, autoionizing and predissociative metastable resonances are generated. However, the computation of complex resonance requires modifications of standard electronic structure codes and methods, which are not always straightforward, in addition, application of complex codes requires more computational efforts. Here we show how resonance eigenvalues, positions and widths, can be calculated using the standard, widely used, electronic-structure packages. Our method enables the calculations of the complex resonance eigenvalues by using analytical continuation procedures (such as Padé). The key point in our approach is the existence of narrow analytical passages from the real axis to the complex energy plane. In fact, the existence of these analytical passages relies on using finite basis sets. These passages become narrower as the basis set becomes more complete, whereas in the exact limit, these passages to the complex plane are closed. As illustrative numerical examples we calculated the autoionization Feshbach resonances of helium, hydrogen anion, and hydrogen molecule. We show that our results are in an excellent agreement with the results obtained by other theoretical methods and with available experimental results.
authors.forename: Arie
authors.initials: A
authors.lastname: Landau
authors.forename: Idan
authors.initials: I
authors.lastname: Haritan
authors.affiliation: Department of Radiation and Chemical Physics at the Institute of Physics , Na Slovance 2, 18221 Prague, Czech Republic.|J. Heyrovsky Institute of Physical Chemistry , Dolejskova 3, 18223 Prague, Czech Republic.
authors.forename: Petra Ruth
authors.initials: PR
authors.lastname: Kaprálová-Žd'ánská
authors.forename: Nimrod
authors.initials: N
authors.lastname: Moiseyev