  We report the implementation of 4-component spinor relativistic
equation-of-motion coupledcluster method within the single- and double-
excitation approximation to calculate ionization potential (EOM-CCSD) of
molecules. We have applied this method to calculate vertical ionization
potentials of the molecules, XH(X=F, Cl, Br, I) along with Cl2 and Br2 in their
closed-shell configuration. We have also presented intermediate results using
2-nd order many-body perturbation theory level in the EOM framework
(EOM-MBPT(2)) to understand the role of electron correlation. All the
calculated values are compared with the available experimental results. Our
results are found to be in well agreement with the sophisticated experiments
and relative deviation of less than 1% achieved for all the considered systems.
