Research

 

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Fields of research

Multi-electron atomic theory, spectroscopy.

Modelling of contemporary atomic theory problems based on usual and symbolic programming.


Research Projects (2020)

Correlation and relativistic effects in multivalency atoms and ions (project supported by University budget). Supervisors: Prof. Dr. G. Gaigalas, research group: Dr. P. Rynkun, Dr. L. Radžiūtė. 2020–2024.
The new program was created. It performs the transformation of atomic state functions from a LSJ-coupled configuration state function (CSF) basis into several other CSF bases such as jj, LK, JK, JJ, and many others. The relativistic multiconfiguration Dirac–Hartree–Fock method is used to compute accurate Landé g-factors for states in B II, C I-IV, Al I-II, Si I-IV, P II, S II, Cl III, Ar IV, Ca I, Ti II, Zr III, and Sn II.

Lithuanian-Japanese project Theoretical Studies of Structure and Properties of Heavy Elements Toward Identification of Gravitational Wave Sources (funded by Research Council of Lithuania (S-LJB-18-1)). Supervisors: Prof. Dr. G. Gaigalas, research group: Dr. P. Rynkun, Dr. L. Radžiūtė. 2018–2020.
For the first time in the world, systematic calculations of the atomic structure were performed for all atoms and ions involved in the r–process. Based on the atomic values obtained in the project, there was performed modelling of the radiation transfer of neutron stars immediately after their merge and a few days later. Based on the results obtained, conclusions needed for astronomical observations of neutron star merger were drawn.

Research Council of Lithuania postdoctoral fellowship Theoretical multipole interference study for gravitational wave sources (Nr. 09.3.3-LMT-K-712-19-0080). Dr. L. Radžiūtė, supervisor Prof. Dr. G. Gaigalas, 2020 – 2022.
Accurate energy levels for the Se II and Te II ions using MCDHF and RCI methods were obtained. The accuracy of results was evaluated comparing energy levels with data from NIST database and other authors. The averaged uncertainty of computed energy levels compared with NIST data was 1.3% and 0.45%, respectively for Se II and Te II ions. Computation of transitions properties and evaluation of it is in progress.

Precision spectral measurements of highly charged rare earth elements and their data analysis with nonempirical MCDF-CI calculation (FY2020 NIFS General Collaboration Project (LHD Experiment), Japan). Supervisors: Prof. F. Koike ir Dr. I. Murakami, research group: Prof. Dr. G. Gaigalas, Dr. Ch. Suzuki, Dr. A. Sasaki, Dr. M. Goto, Dr. D. Kato, Dr. T. Kato, Dr. H. Sakaue, 2020.
It was measured spectral data of La, Pr ir Eu elements by SOXMOS and EUV spectrometers, which was prepared to use as parts of the LHD device. Using the newly developed version of the GRASP package: GRASP2018, we have performed the identification of the newly observed lines by comparing them with newly calculated non empirical theoretical values. The present research of lanthanide spectra gives deep insight of the spectral structures as well as the structures of heavy atomic many electron ions. The result will also be valuable and useful to the neighboring field such as plasma diagnostics for nuclear fusion research.

 

Research Projects (2019)

Correlation and relativistic effects in complex atoms and ions (project supported by University budget). Supervisors: Prof. Dr. G. Gaigalas, research group: Dr. P. Rynkun, Dr. L. Radžiūtė. 2015–2019.
New method of continuum wave functions computation was demonstrated for Xe atom. EDM moments were computed and continuum contribution to the atom electric dipole moment (EDM) was evaluated. New version of GRASP programme package was prepared and published in the latest Fortran 95 version. New version of the program for relativistic isotope shift computations (RIS4) was prepared.

Lithuanian-Japanese project Theoretical Studies of Structure and Properties of Heavy Elements Toward Identification of Gravitational Wave Sources (funded by Research Council of Lithuania (S-LJB-18-1)). Supervisors: Prof. Dr. G. Gaigalas, research group: Dr. P. Rynkun, Dr. L. Radžiūtė. 2018–2020.
By employing multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, we calculated the energy levels and transition data of electric dipole transitions for singly ionized lanthanides. Comparing with various databases we obtained ten times more data for lanthanides, with 10% accuracy. Investigation was done on Nd III, Er III and Nd IV ions. The accuracy  was up to 10%. Based on these elements analysis on opacity was done. The results of the above mentioned research have attracted interest of international research community and have been publicized  by Eurekalert at https://www.eurekalert.org/pub_releases/2019-03/nion-fsa031119.php.

Research Council of Lithuania postdoctoral fellowship Theoretical study of atomic parameters with applications to astrophysics (Nr. 09.3.3-LMT-K-712-02-0072). Dr. P. Rynkun, supervisor Prof. Dr. G. Gaigalas, 2017 – 2019.
We obtained accurate and extensive results of electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2) transition for Cl III and Ar IV ions using MCDHF and RCI methods. The accuracy of results was evaluated comparing energy levels with data from NIST database and by the agreement of transition rates between length and velocity gauges. The averaged uncertainty of computed energy levels compared with NIST data was 0.18% and 0.21%, respectively for Cl III and Ar IV ions. The mean dT for all presented E1 transitions is 5.95% and 6.47%, respectively, for the Cl III and Ar IV ions.

 

Research Projects (2018)

Correlation and relativistic effects in complex atoms and ions (project supported by University budget). Supervisors: Prof. Dr. G. Gaigalas, research group: Dr. P. Rynkun, Dr. L. Radžiūtė. 2015–2019.
The relativistic multiconfiguration Dirac–Hartree–Fock method was used to compute excitation energies and lifetimes for the 143 lowest states of the 3s23p3, 3s3p4, 3s23p23d, 3s3p33d, 3p5, 3s23p3d2 configurations in P-like ions from Cr X to Zn XVI. Multipole (E1, M1, E2, M2) transition rates, line strengths, oscillator strengths, and branching fractions among these states are also given. Computed excitation energies were compared with the NIST and CHIANTI compiled values and previous calculations.

Lithuanian-Japanese project Theoretical Studies of Structure and Properties of Heavy Elements Toward Identification of Gravitational Wave Sources (funded by Research Council of Lithuania (S-LJB-18-1)). Supervisors: Prof. Dr. G. Gaigalas, research group: Dr. P. Rynkun, Dr. L. Radžiūtė. 2018–2020.
By employing multiconfiguration Dirac-Hartree-Fock and relativistic configuration interaction methods, we calculated energy levels and transition data of electric dipole transitions for Nd II ion. Compared with previous calculations, our new results provided better agreement with the experimental data. The accuracy of energy levels in the present work was achieved 10 %, comparing with the NIST database.

Research Council of Lithuania postdoctoral fellowship Theoretical study of atomic parameters with applications to astrophysics (Nr. 09.3.3-LMT-K-712-02-0072). Dr. P. Rynkun, supervisor Prof. Dr. G. Gaigalas, 2017 – 2019.
We obtained accurate and extensive results of electric dipole (E1), magnetic dipole (M1), and electric quadrupole (E2) transition for S II ion using MCDHF and RCI methods. The accuracy of results was evaluated comparing energy levels with data from NIST database and by the agreement of transition rates between length and velocity gauges. Some levels of the calculated ions were presented for the first time.

Construction of Atomic Data and Radiative Transfer Simulations toward Identification of Gravitational Wave Sources and the Origin of Heavy Elements (National Institutes of Natural Sciences (NINS, Japan). International research project). Prof. Dr. G. Gaigalas, 2016–2018.
We obtained opacities from bound-bound transitions for Se, Ru, Te, Ba, Nd, and Er. We showed that the optical brightness can be different by >2 mag depending on the element abundances in the ejecta such that post-merger, lanthanide-free ejecta produce brighter and bluer optical emission. Such blue emission from post-merger ejecta can be observed from the polar directions if the mass of the preceding dynamical ejecta in these regions is small.


Dissemination of research results (2018 – present)

Iš čia kylame į žvaigždes: pakeliui į naujos mokslinių tyrimų srities vystymą – Fizikos fakultetas (vu.lt)

VU TFAI mokslininkų straipsnis – pasaulyje pripažintame astrofizikos žurnale – Vilniaus universitetas

プレスリリース / 自然科学研究機構 核融合科学研究所 (nifs.ac.jp)

Press Release / National Institute for Fusion Science (NIFS)

核融合科学と天文学の協力で解き明かす、宇宙の重元素の起源 | 国立天文台(NAOJ)

Cross-Disciplinary Collaboration Enables Investigation of the Origin of Heavy Elements | NAOJ: National Astronomical Observatory of Japan – English

中性子星合体からの光を分析する世界最高精度の原子データの構築 ―核融合科学と天文学の協力で重元素の起源を紐解く― | CfCA – Center for Computational Astrophysics (nao.ac.jp)

Fusion Science and Astronomy Collaboration Enables Investigation of the Origin of Heavy Elements | CfCA – Center for Computational Astrophysics (nao.ac.jp)

Fusion science and astronomy collaboration enables investigation of the origin of heavy elements | EurekAlert! Science News

SPECTRUM30_el_versija.pdf (vu.lt)

Labai mažos žvaigždės – labai didelio mokslo proveržio šaltinis – LRT

Labai mažos žvaigždės – labai didelio mokslo proveržio šaltinis | VU naujienos