Quantum Size Effects in $\delta $ -- Pu (111) and (110) Films*

First-principles full-potential linearized-augmented-plane-wave (FP-LAPW) calculations have been carried out for $\delta $-Pu (111) and (110) films up to seven layers. The layers have been studied at the non-spin-polarized-no-spin-orbit coupling (NSP-NSO), non-spin-polarized-spin-orbit coupling (NSP-SO), spin-polarized-no-spin-orbit coupling (SP-NSO), spin-polarized-spin-orbit coupling (SP-SO), anti-ferromagnetic-no-spin-orbit coupling (AFM-NSO), and anti-ferromagnetic-spin-orbit-coupling (AFM-SO) levels of theory. The ground state of both $\delta $-Pu (111) and (110) films is found to be at the AFM-SO level of theory and the surface energy is found to rapidly converge. The semi-infinite surface energy for $\delta $-Pu (111) and (110) films is predicted to be 1.18 and 1.42 J/m$^{2}$, while the magnetic moments show an oscillating behavior, gradually approaching the bulk value of zero with increase in the number of layers. Work functions indicate a strong quantum size effect up to and including five layers for the (111) surface and seven layers for the (110) surface, respectively. The work functions of $\delta $-Pu (111) and (110) films at the ground state are predicted be 3.41 and 2.99eV, respectively. *This work is supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, Department of Energy (Grant DE-FG02-03ER15409) and the Welch Foundation, Houston, Texas (Grant Y-1525).