The article deals with the general implementation of the four-component spinor relativistic extended-coupled-cluster (ECC) method to calculate first-order property of atoms and molecules in their open-shell ground-state configuration. The implemented relativistic ECC is employed to calculate hyperfine structure constants of alkali metals (Li, Na, K, Rb, and Cs), singly charged alkaline-earth-metal atoms $({\mathrm{Be}}^{+},{\mathrm{Mg}}^{+},{\mathrm{Ca}}^{+}$, and ${\mathrm{Sr}}^{+})$, and molecules (BeH, MgF, and CaH). We have compared our ECC results with the calculations based on the restricted active space configuration interaction (RAS-CI) method. Our results are in better agreement with the available experimental values than those of the RAS-CI values.

• Received 24 September 2014
• Revised 28 November 2014

DOI:https://doi.org/10.1103/PhysRevA.91.022512