Spectral properties of $\delta$-plutonium: Sensitivity to $5f$ occupancy

By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of $\delta$-plutonium with varying $5f$ occupancy. The LDA Hamiltonian is extracted from a tight-binding fit to full-potential linearized augmented plane-wave calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and by the Hubbard-I approximation. We demonstrate strong sensitivity of the spectral properties to the $5f$ occupancy, which suggests using this occupancy as a fitting parameter in addition to the Hubbard $U$. By comparing with photoemission data, we conclude that the “open shell” $5f^5$ configuration gives the best agreement, resolving the controversy over $5f$ “open shell” versus “close shell” atomic configurations in $\delta \text{−}\mathrm{Pu}$.

Figure 1

(Color) The $5f$ spectral density calculated from the DMFT(HI) (left panels) and DMFT(QMC) (right panels) for $\delta \text{−}\mathrm{Pu}$ for varying $5f$ site energy at $T=632\mathrm{K}$. In all panels, the spectral densities contributed from the $j=5∕2$ and $j=7∕2$ subshells are represented by the black and red lines, respectively. The total $5f$ spectral density is represented by the blue line. The energy $E=0$ denotes the position of the Fermi level.

Figure 2

(Color) (a) Experimental and theoretical photoemission spectrum. (b) The $5f$ spectral density calculated from the DMFT(HI) with only $F^0=U_f$ (black line) and full Coulomb (red line) interactions for $n_f=5.0$. (c) The $5f$ spectral density calculated from the DMFT(HI) with full Coulomb interactions for $n_f=5.2$ and scaled and/or shifted ones for $n_f=5.0$ and 6.0. Here, $E_1=E+0.87\mathrm{eV}$ and $E_2=E-2.29\mathrm{eV}$.