Investigation on radiative transitions of K-shell excited states of Be-like Mn21+ ion

This work performs fully relativistic calculations on the K-shell excited states of Be-like Mn 21 + ion via the multi-configuration Dirac–Hartree–Fock (MCDHF) method combined with relativistic configuration interaction (RCI), using the GRASP2018 package. Systematic computations are implemented for typical K-shell excited configurations including 1 s 2 s 2 n l , 1 s 2 s 2 p n l , and 1 s 2 p 2 n l ( n ≤ 3 , l = s , p , d ) . Large-scale configuration state function expansions with an active orbital space up to n ≤ 9 are adopted, fully accounting for Breit interaction and quantum electrodynamics (QED) corrections. In total, 2689 electric dipole (E1) transition parameters, including energy levels, wavelengths, transition probabilities, line strengths, and oscillator strengths are derived. An optimized uncertainty evaluation method combined with NIST grading standards is employed to assess the reliability of the present data. Most calculated spectral wavelengths exhibit relative deviations within 0.08% compared with previously reported theoretical results, confirming the high precision and good numerical convergence of the present dataset. By comparative investigations of E1 transition parameters between Be-like Sc 17 + and Mn 21 + ions, we reveal distinct behaviours of QED and Breit relativistic corrections, enhancement in configuration mixing induced by spin–orbit coupling, as well as the finding that intensified configuration mixing does not necessarily degrade the computational precision of configuration-interaction calculations. This work constructs a self-consistent, high-precision atomic benchmark database for K-shell excited states of Mn 21 + ions, fills the data deficiency in inner-shell excitation parameters for intermediate- Z Be-like ions, and provides accurate theoretical references for astrophysical spectral identification, fusion plasma diagnostic analysis, and radiative-collisional modelling.