We present a high-precision study of the ionization potential (IP) and electron affinity (EA) of superheavy element 119 (E119). Accurate IP and EA values for E119 are important for providing benchmarks for future experimental research investigating periodic-law trends beyond oganesson.

Electronic correlation was treated within the relativistic single-reference coupled-cluster theory with single, double, and iterative triple excitations, SR-CCSD(T). Contributions up to triple and perturbative quadruple cluster amplitudes in the SR-CCSDT(Q) method were included to account for electron correlation beyond the SR-CCSD(T) model. For this purpose, a compact atomic natural orbital (ANO)-like set was constructed. The corrections arising from the Gaunt electron–electron interaction and quantum-electrodynamic (QED) effects were evaluated. Extensive tests of the basis set and correlation convergences were performed and a detailed uncertainty analysis was carried out.

Two different schemes for constructing Dirac–Hartree–Fock orbitals were used to calculate the IP and EA of E119. Inclusion of high-order amplitudes significantly reduces the discrepancy between calculations employing different schemes. Enlarging the basis set leads to an increase in the IP, whereas the EA is less sensitive to the addition of new functions. The calculated Gaunt and QED corrections are small but non-negligible within estimated uncertainties. The dominant sources of uncertainty are the ghi-functions and high-order excitations.

Our final values for IP and EA are 4.7839(56) and 0.6750(71) eV, respectively. These results tighten previous estimates and provide a reliable theoretical reference for future experiments.