The Z-vector technique , which is equivalent to the Lagrange multiplier method for the first-order properties, is a popular energy-derivative approach within the CC theory for the precise calculation of various firstorder static molecular properties. Interested reader can see Refs. and for more details about the Z-vector method. The Z-vector approach was introduced into the four-component relativistic CCSD framework to accurately predict various properties of molecules by Pal and co-workers . In this approach, a perturbation independent linear operator (Λ) is used for the evaluation of the energy-derivative. For the CCSD approximation, Λ = Λ 1 + Λ 2 and is defined as