First-principles DFT+DMFT calculations of structural properties of actinides: Role of Hund's exchange, spin-orbit coupling, and crystal structure

Abstract

We utilize a combination of an ab initio calculation of effective Coulomb interactions and a DFT+DMFT calculation of total energy to study the structural properties of pure actinides. We first show that the effective direct Coulomb interactions in plutonium and americium are much smaller than usually expected. Secondly, we emphasize the key role of Hund's exchange in combination with the spin-orbit coupling in determining the structural parameters of $\ensuremath{\delta}$-plutonium and americium. Thirdly, using this ab initio description, we reproduce the experimental transition from low volume early actinides (uranium, neptunium, $\ensuremath{\alpha}$-plutonium) to high-volume late actinides ($\ensuremath{\delta}$-plutonium, americium, and curium) without the need of an artificial magnetism. Finally, we compare the energies and structural properties of $\ensuremath{\alpha}, \ensuremath{\gamma}, \ensuremath{\epsilon}$, and $\ensuremath{\delta}$ phases of plutonium to experimental data.