Theoretical investigation on forbidden transition properties of fine-structure splitting in ²D state for K-like ions with 26 ≤ Z ≤ 36

Excitation energies, magnetic dipole, and electric quadrupole transition probabilities of the 3d ²D_3/2-3d ²D_5/2 transition in the potassium-like (K-like) sequence with 26 ≤ Z ≤ 36 are investigated by using the multi-configuration Dirac-Hartree-Fock (MCDHF) method. The contributions of the electron correlations, Breit interaction, and the leading-order quantum electrodynamic (QED) effects on the transition properties are analyzed. The present results are interested in the laboratory tokamak and the astronomical observations. Furthermore, the feasibility of these ions for the highly charged ion (HCI) clocks is discussed. Considering the wavelength of lasers and manipulation process of the atomic clocks, Cu¹⁰⁺ and Zn¹¹⁺ are recommended as promising candidates with achievable quality factors at the 10¹⁵ level.