Electron affinities of the actinide atoms from relativistic coupled cluster

Abstract

The electron affinities (EAs) of the actinide atoms Ac–Pu and Bk–Lr have been calculated using the CCSD(T) method with sequences of large correlation consistent basis sets extrapolated to the complete basis set limit. The Am and Cm systems were too multideterminantal to be amenable to the present treatment. Spin–orbit effects have been included variationally using relativistic 4-component CCSD(T) throughout, and both 6d and 7p electron attachments have been investigated. The small effects due to quantum electrodynamics have also been included in all cases at the Dirac–Hartree–Fock level of theory. In a few cases (Ac, Th, Pu, No, and Lr), it was possible to include contributions from correlation beyond the CCSD(T) level of theory up to CCSDT(Q). The latter was particularly important for the 6d electron affinities of both Ac and Th. For the early actinides Ac through Np, stable anions are predicted for both 6d and 7p electron attachments, but except for the Th atom, the largest EAs occur when the additional electron is attached to the 7p orbital. The Pu atom is predicted to only slightly bind an electron with an EA of just 0.63 kcal/mol, while Bk–No are predicted to not bind an electron within the accuracy of the present calculations. In the two cases where accurate experimental values exist, Th and U, the agreement with the present results are within 0.1 and 0.3 kcal/mol, respectively, although the CCSD(T) level of theory is not sufficient to unambiguously determine the ground state of U−.