The Theoretical Spectroscopy Group at Vilnius University focuses on the production of various spectroscopic parameters such as level energies, spontaneous transition wavelengths and probabilities, absorption oscillators strengths, radiative lifetimes, Landé g-factors for light and heavy atoms and ions, including highly charged ones.
Our ab initio calculation of the spectroscopic data is performed in a quasirelativistic Hartree-Fock (QRHF) approach with transformed radial orbitals (TRO) implemented in the original computer code developed at VU Institute of Theoretical Physics and Astronomy. This QRHF approximation applied in our investigation is quite unique one and significantly differs from other widely-utilized relativistic or quasirelativistic methods especially in constructing one-electron radial orbitals.
For the level energy calculation, we include all two-electron interactions in the same way as it is done in conventional Breit–Pauli approximation. This similarity makes it possible to apply widely used tools for the angular integration of the Breit-Pauli Hamiltonian matrix elements and codes for the radiative transition operator matrix elements which have been adopted specifically for use with the QRHF radial orbitals. The electron correlation effects are included using a common configuration interaction (CI) approximation. The one-electron orbitals of configurations under consideration are determined by solving the QRHF equations. The virtually excited electrons of admixed (correlation) configurations included in CI are described by TROs with variable parameters. Originally the method of transformed radial orbitals was developed for the usual Hartree-Fock approximation and successfully used for investigation of the medium-Z ions. Consequently this method was adopted to the quasirelativistic radial orbitals.
We apply both quasirelativistic and non-relativistic radial orbitals in our codes to acquire theoretical spectroscopic data needed in fusion plasma and astrophysical research. Utilization of the QRHF+TRO approach makes it possible to produce atomic spectroscopic parameters for the multi-electron multi-charged heavy ions, including tungsten ions. This work has started within EURATOM framework and it is still ongoing in studies of the ground and excited levels of high-Z species. For the low-ionization atoms, usually a standard non-relativistic CI approximation based on the HF+TRO orbitals ensures that generated spectroscopic parameters are accurate enough for their application in astronomy and in astrophysical models. Here our main priority is to assess and evaluate the accuracy of produced spectral data. We continue to maintain and constantly update an open-access database for theoretical atomic data ADAMANT at Vilnius University which contains our generated spectroscopic and other atomic data for numerous ions.
Dr Romualdas KISIELIUS
Institute of Theoretical Physics and Astronomy, Vilnius University, Saulėtekio al. 3, Vilnius, LT-10257, Lithuania
Phone: +370 64641632