First principles calculations of the structure and elastic constants of α, β and γ uranium

Abstract

This study analyzes structural and elastic properties of five uranium crystal structures: the face centered orthorhombic A20 (α phase), the tetragonal D8b (β phase), body centered tetragonal (bct), body centered cubic (γ phase) and face centered cubic structures. Calculations are performed within the density functional theory framework employing the Projector Augmented Wave method and the Perdew–Burke–Ernzerhof generalized gradient approximation (PBE–GGA) of the exchange correlation. The elastic constants are used to compute polycrystalline elastic moduli, Poisson’s ratio and the Debye temperature for all five structures. The α and γ phase properties are compared with theoretical and experimental results. The complex tetragonal 30atom beta phase is examined in detail. Representation of the β phase by a bct structure is examined; we find that the structure of the β phase is significantly different from the bct phase but exhibits similar elastic properties. This is the first comprehensive investigation into the elastic constants of uranium utilizing the PBE–GGA.