arXiv subjects

L. Kitovienė

Publications and source records attributed to L. Kitovienė.

7 recordsLinked to original sources

arXiv2026

Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Three-Particle Feynman Diagram Contribution to Valence-Valence Correlations

The method based on the second-order perturbation theory to identify the most important configuration state functions of the various correlations is extended to include valence-valence correlations, which are described by the three-particle Feynman diagram. The extension presented in this work complements the core-valence, core, core-core, and valence-valence correlations which were developed in a series of previous papers by G. Gaigalas, P. Rynkun and L. Kitovienė. Whereas these valence-valence correlations are described by the three-particle Feynman diagram, additional developments to calculate the spin-angular parts of this diagram have been made to the program library librang of the Grasp. As an example of the application of the developed method, the atomic calculations of the energy structure for the Se III are presented. In the present work, this method was also used to select the most significant configuration state functions and to use this basis to solve the self-consistent field equations.

physics.atom-ph↗

arXiv2026

Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Three-Particle Feynman Diagram Contribution to Core-Valence Correlations

In order to ascertain the precise atomic characteristics, it is important to incorporate a wide range of electron correlations in the computational analysis. However, it is important to note that undertaking such studies will result in substantial increases of the CSF expansions. The present publication, as well as the series of articles that have been published by G. Gaigalas, P. Rynkun, and L. Kitovienė, are dedicated to the analysis and resolution of the problem in question. In this series, a method was developed based on second-order perturbation theory to identify the most important core-valence, core, core-core, and valence-valence correlations. The method under discussion is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form. In this study, the method is further expanded to encompass additional core-valence electron correlations of the third and fourth types. Conversely, the correlations that are not encompassed by perturbation theory are addressed in a conventional manner. This method can be used to calculate the properties of an atom or ion with any number of valence and core electrons. As an example of its application, the atomic calculations of the energy structure and lifetime for Ne II are presented.

physics.atom-ph↗

arXiv2026

Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Core Correlations

The paper presents a further development of the method G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order of Rayleigh-Schrödinger Perturbation Theory for the {\sc Grasp}2018 Package: Core-Valence Correlations, {\em Lithuanian Journal of Physics}, 64, No. 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 meanwhile relativistic configuration interaction accounts for the rest of correlations. This allows a significant reduction of the space of the configuration state function for complex atoms and ions. We also demonstrate how this method works for energy structure calculation of Fe XV ion.

physics.atom-ph↗

arXiv2026

Second-Order Rayleigh-Schrödinger Perturbation Theory for the GRASP2018 Package: Core-Core Correlations

Grasp package is based on the relativistic configuration interaction in which accurate calculations, accounting for valence, valence-valence, core-valence, core, and core-core electron correlations, often rely on massive CSF expansions. This paper presents further development of the method based on the second-order perturbation theory for finding the most important CSFs that have the greatest influence on the core-valence, core, and core-core correlations. This method is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form [G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core-Valence Correlations, Lithuanian Journal of Physics, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3) and G. Gaigalas, P. Rynkun, L. Kitovienė, Second-Order Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Core Correlations, Lithuanian Journal of Physics, 64, No. 2, 73-81 (2024) (https://doi.org/10.3952/physics.2024.64.2.1)]. In this extension, the perturbation theory accounts for electron core-valence, core, and core-core correlations where an atom or ion has any number of valence electrons for calculation of energy spectra and other properties. Meanwhile the rest of the correlations are accounted for in a traditional way. This allows a significant reduction of the space of the configuration state function for complex atoms and ions. We also demonstrate how this method works for calculations of the energy structure and E1 transition properties of Fe XV ion.

physics.atom-ph↗

arXiv2026

Second-Order Rayleigh-Schrödinger Perturbation Theory for the Grasp2018 Package: Valence-Valence Correlations

The accurate description of electron correlations remains a major challenge in atomic calculations. In order to perform accurate calculations, it is necessary to consider the various types of electron correlations what often leads to extensive CSF expansions. This work presents further development of the method based on the second-order perturbation theory to identify the most significant CSFs that have the greatest influence on core-valence, core, core-core and valence-valence correlations. This method is based on a combination of the relativistic configuration interaction method and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in an irreducible tensorial form [G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 1, 20-39 (2024) (https://doi.org/10.3952/physics.2024.64.1.3), G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 2, 73-81 (2024) (https://doi.org/10.3952/physics.2024.64.2.1) and G. Gaigalas, P. Rynkun, L. Kitovienė, Lithuanian Journal of Physics, 64, No. 3, 139-161 (2024) (https://doi.org/10.3952/physics.2024.64.3.1)]. The method is extended to include additionally valence-valence electron correlations. It can be applied for an atom or ion with any number of valence electrons for calculation of energy spectra and other properties. Meanwhile, the correlations which can not be included according to perturbation theory are accounted for in a regular way. The use of the developed method allows a significant reduction of CSFs especially for complex atoms and ions. As an example of its application, the atomic calculations of the energy structure for Se~III ion are presented.

physics.atom-ph↗

arXiv2026

Second-order Rayleigh-Schrödinger Perturbation Theory for the {\sc Grasp}2018 Package: Core-valence Correlations

The General Relativistic Atomic Structure package [{\sc Grasp}2018, C. Froese Fischer, G. Gaigalas, P. Jönsson, J. Bieroń, Comput. Phys. Commun. (2019), DOI: 10.1016/j.cpc.2018.10.032], is based on multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction (RCI) methods for energy structure calculations. Atomic state function used in the program is built from the set of configuration state functions (CSFs). The valence-valence, core-valence and core-core correlations are explicitly included through expansions over CSFs in RCI. We present a combination of RCI and the stationary second-order Rayleigh-Schrödinger many-body perturbation theory in irreducible tensorial form to account for electron core-valence correlations when an atom or ion has any number of valence electrons. This newly developed method, which offers two ways of use, allows a significant reduction of the CSF space for complex atoms and ions. We also demonstrate how the method and program works for energy structure calculation of Cl III element.

physics.atom-ph↗

arXiv2024

Theoretical investigation of energy levels and transitions for Ce III with applications to kilonova spectra

Doubly ionized cerium (Ce$^{2+}$) is one of the most important ions to understand the kilonova spectra. In particular, near-infrared (NIR) transitions of Ce III between the ground (5p$^6$ 4f$^2$) and first excited (5p$^6$ 4f 5d) configurations are responsible for the absorption features around 14,500 A. However, there is no dedicated theoretical studies to provide accurate transition probabilities for these transitions. We present energy levels of the ground and first excited configurations and transition data between them for Ce III. Calculations are performed using the GRASP2018 package, which is based on the multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods. Compared with the energy levels in the NIST database, our calculations reach the accuracy with the root-mean-square (rms) of 2732 cm$^{-1}$ or 1404 cm$^{-1}$ (excluding one highest level) for ground configuration, and rms of 618 cm$^{-1}$ for the first excited configuration. We extensively study the line strengths and find that the Babushkin gauge provide the more accurate values. By using the calculated gf values, we show that the NIR spectral features of kilonova can be explained by the Ce III lines.

astro-ph.HE↗