Abstract
We develop a new implementation of the Gutzwiller approximation in combination with the local density approximation, which enables us to study complex and systems beyond the reach of previous approaches. We calculate from first principles the zero-temperature phase diagram and electronic structure of Pr and Pu, finding good agreement with the experiments. Our study of Pr indicates that its pressure-induced volume-collapse transition would not occur without change of lattice structure—contrarily to Ce. Our study of Pu shows that the most important effect originating the differentiation between the equilibrium densities of its allotropes is the competition between the Peierls effect and the Madelung interaction and not the dependence of the electron correlations on the lattice structure.
- Received 26 May 2014
DOI:https://doi.org/10.1103/PhysRevX.5.011008
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Published by the American Physical Society
Popular Summary
Understanding the connection between -electron localization and volume-collapse transitions is an ongoing puzzle in condensed-matter theory. In several -electron materials, changes in pressure and temperature can induce volume-collapse transitions, i.e., sudden changes in volume and/or lattice structure. In many cases, such as cerium, this phenomenon occurs concomitantly with a sudden localization or delocalization of the electrons. Other -electron materials, such as americium, can display volume-collapse transitions with no concomitant appreciable change in electronic structure. Making sense of these different trends requires first-principles calculations able to describe both the electronic structure and the thermodynamical properties of -electron systems. However, the methods currently available are computationally too time consuming to be practically applicable for this purpose.
We develop new methods and algorithms that enable us to study the crystalline phases of plutonium (Pu) and praseodymium (Pr), two prototypical materials with partially delocalized electrons. Our study of Pr demonstrates that its pressure-induced volume-collapse transition is not driven only by -electron delocalization. In fact, this phenomenon could not occur without changes in the lattice structure. This finding sheds light on the fact that there exist -electron materials that display pressure-induced volume-collapse transitions with no concomitant delocalization. Our calculations of Pu reveal that the most important effect resulting in large differences between the equilibrium densities of its allotropes is not the dependence of the electron correlations on the lattice structure, which we find to be negligible. Our theoretical approach did not require us to introduce any artificial spin and/or orbital polarization, which was necessary in previous first-principles calculations of Pu.
Our calculations are in good agreement with experiments, and they pave the way for a better understanding of the temperature-dependent properties of Pu. Furthermore, they demonstrate that the methods presented in this work can be employed to study complex -electron systems beyond the reach of previous approaches.
