We discuss the four-component relativistic total energies (TEs) and correlation energies (CEs) with and without the no virtual pair approximation (NVPA). The system considered is the He isoelectronic sequence from 2He to 116Uuh114+. It is shown that the full configuration interaction TEs and CEs with the NVPA depend on the methods used to generate atomic orbitals (AOs); without the NVPA the values are independent of how the AOs are generated. This result shows the importance of contributions from the Dirac sea where the electrons kinetic energies are negative.
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