Orbital-selective correlations and angular momentum coupling in heavy actinides Am, Cm, Bk, and Cf under pressure: A many-body perspective

We systematically investigate the electronic structures of americium (Am), curium (Cm), berkelium (Bk), and californium (Cf) in both the ambient-pressure double hexagonal close-packed (dhcp) and high-pressure face-centered cubic (fcc) phases, using density functional theory combined with embedded dynamical mean-field approach. Our results reveal that Am exhibits moderate correlation strength and localized 5f states dominated by jj angular momentum coupling scheme. In Cm and Bk, strong electron correlations drive the system into a localized regime, characterized by Hubbard band formation, large effective electron masses, and non-Fermi liquid behavior. Their magnetic ground states are governed by exchange interactions within an intermediate coupling scheme that shifts toward LS coupling. Remarkably, Cf reenters a jj coupling regime while exhibiting the strongest orbital-selective correlations among the series. Atomic eigenstate probabilities show moderate configurational mixing in Am, whereas Cm, Bk, and Cf maintain nearly fixed trivalent configurations, indicating localized 5f states. Compared with the dhcp phase, the fcc structure generally enhances correlation effects, as evidenced by wider Hubbard bandgaps and increased valence state fluctuation in Am. Analyses of kinetic energy, potential energy, spin susceptibility, and charge susceptibility further corroborate the progressive localization of 5f electrons and the emergence of orbital-selective correlations from Am to Cf. This work establishes a unified picture of 5f electron evolution across the Am-Cf series, elucidating the interplay between spin-orbit coupling, electron correlation, and crystal structure in heavy actinides and offering insights into their behavior under high pressure.