Localization of 5f electrons and phase transitions in americium

摘要

Density-functional electronic calculations have been used to investigate the high-pressure behaviour of americium. The phase transitions calculated agree with the recent sequence obtained experimentally under pressure: double hexagonal close packed (P6(3)/mmc) --> face-centred cubic (Fm (3) over barm) --> face-centred orthorhombic (Fddd) -->) primitive orthorhombic (Pnma). In the first three phases the 5f electrons are found localized; only in the fourth phase (Am IV) are the 5f electrons found delocalized. The localization of the 5f electrons is modelled by an anti-ferromagnetic configuration which has a lower energy than the ferromagnetic ones. In this study the complex crystal structures have been fully relaxed.