  We employ four-component spinor relativistic equation-of-motion
coupled-cluster (EOMCC) method within the single- and double- excitation
approximation to calculate the single ionization potentials (IPs) and double
ionization potentials (DIPs) of the He and Be isoelectronic sequences up to Ne.
The obtained results are compared with the available results from the National
Institute of Standards and Technology (NIST) database to test the performance
of the EOMCC method. We also present intermediate results at different level of
approximations in the EOMCC framework to gain insight of the effect of electron
correlation. Furthermore, we investigate the dependence of the IPs and DIPs of
these ions on the ionic charge and observe that these follow parabolic trends.
Comparison between the trends of IPs and DIPs in both the classes of considered
systems are categorically demonstrated.

Atomic Physics