Effects of spin–orbit coupling on actinium under pressure

Abstract

AbstractActinium (Ac) is a radioactive metal and the first element of the actinide series. At ambient conditions Ac crystallizes in the fcc lattice, however, up to date its phase diagram is unknown. In the present work, we have studied the structural and electronic properties of Ac under hydrostatic pressure assuming the fcc structure as well as three hypothetical structures, namely the hcp, bcc, and sc, and for pressures up to 100 GPa. From our calculations, we found only one structural transition allowed, from the fcc to hcp, our calculated pressure was 39.85 GPa. The calculations were performed by means of the full potential linearized augmented plane wave (FLAPW) method and the generalized gradient approximation (GGA) for the exchange–correlation energy, where we have included in our study the spin–orbit coupling which is important for heavy elements. The total energy results were fitted to the third order Birch–Murnaghan's equation of state.