Free-energy calculations for plutonium

摘要

We have calculated the free energy of δ and εplutonium at T = 900 K. We find that in spite of having amuch higher energy than δ-Pu at zero temperature, theε phase is favored at high temperatures in agreement withthe experimental phase diagram. The most importanttemperature-dependent contribution to the free energy isdetermined to be the anharmonic lattice vibrations.We have thus in this study resolved the concern overthe high ε-Pu energy in the DFT prediction. Ourconclusions generally echo that of but there aresubstantial differences in parts of the theory. First, we modelplutonium with full-potential (no geometricalapproximations) calculations that include spin-orbital andorbital-orbital interactions. Second, our phonon modelincludes anharmonic lattice vibrations at finite temperatures.