  The open-shell reference relativistic equation-of-motion coupled-cluster
method within its four-component description is successfully implemented with
the consideration of single- and double- excitation approximation. The one-body
and two-body matrix elements required for the correlation calculation are
generated using Dirac-Coulomb Hamiltonian. As a first attempt, the implemented
method is employed to calculate a few of the low-lying ionized states of heavy
atomic (Ag, Cs, Au, Fr, Lr) and valence ionization potential of molecular (HgH,
PbF) systems, where the effect of relativity does really matter to obtain
highly accurate results. Not only the relativistic effect, but also the effect
of electron correlation is crucial in these heavy atomic and molecular systems.
To justify the fact, we have taken two further approximations in the
four-component relativistic equation-of-motion framework to quantify how the
effect of electron correlation plays a role in the calculated values at
different level of the approximation. All these calculated results are compared
with the available experimental data as well as with other theoretically
calculated values to judge the extent of accuracy obtained in our calculations.
A nice agreement is achieved for all the considered systems which validates the
performance of the open-shell reference relativistic equation-of-motion
coupled-cluster method.
