Email: gediminas.gaigalas@tfai.vu.lt; pavel.rynkun@tfai.vu.lt;
laima.radziute@tfai.vu.lt
The paper presents a further development of
the method presented in G. Gaigalas, P. Rynkun, and L.
Kitovienė, Second-order Rayleigh–Schrödinger perturbation
theory for the GRASP2018 package: core–valence correlations,
Lith. J. Phys. 64(1), 20–39 (2024)
(https://doi.org/10.3952/physics.2024.64.1.3), based on a
combination of the relativistic configuration interaction
method and on the stationary second-order Rayleigh–Schrödinger
many-body perturbation theory in an irreducible tensorial
form. In this extension, the perturbation theory accounts for
both electron core–valence and core correlations when an atom
or ion has any number of valence electrons, while the
relativistic configuration interaction accounts for the rest
of correlations. This allows a significant reduction of the
space of the configuration state functions for complex atoms
and ions. We also demonstrate how this method works for the
energy structure calculation of Fe XV ion.
Keywords: configuration interaction, spin-angular
integration, perturbation theory, tensorial algebra,
core–valence correlations, core correlations
* Dedicated to the memory of professor Adolfas
Jucys (1904–1974), pioneer of contemporary theoretical
physics in Lithuania, initiator of the ‘Lithuanian Physics
Collection’, on the occasion of his birth and death
anniversaries.
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