Electronic and phonon properties of six crystalline phases of Pu metal

In the light actinides Th to Np, and in the low-temperature {α} phase of Pu, the $5f$ electrons are itinerant, while in the five higher-temperature phases of Pu, and in the heavy actinides from Am on, the $5f$ electrons are localized to varying degrees. To understand the physics of $5f$ localization is a current problem in electronic-structure theory. The kind of experimental data that can help in solving this problem is not available. In this paper, thermodynamic data for Pu metal are analyzed to extract the quantities important for electronic-structure theory. For each of the six crystal phases, the following quantities are evaluated: (a) the static lattice potential, which is the ground-state energy of electronic-structure calculations, (b) central moments of the phonon distribution, which can be compared to any theoretical calculation of phonon frequencies, and (c) a measure of combined anharmonic and electronic excitation contributions to entropy, which contains information on the electronic density of states. Though at present we are not able to separate anharmonic and electronic excitation effects, the last named quantity will help to do so in the future.