An dynamical-mean-field-theory investigation of specific heat and electronic structure of $α$ and $δ$-plutonium

Abstract

We have carried out a comparative study of the electronic specific heat and electronic structure of $α$ and $δ$-plutonium using dynmical mean field theory (DMFT). We use the perturbative T-matrix and fluctuating exchange (T-matrix FLEX) as a quantum impurity solver. We considered two different physical pictures of plutonoium. In the first, $5{f^5}+$, the perturbative treatment of electronic correlations has been carried out around the non-magnetic (LDA) Hamiltonian, which results in an f occupation around a bit above $n_f = 5 $. In the second, $5{f^6}-$, plutonium is viewed as being close to an $5{f^6}$ configuration, and perturbation theory is carried out around the (LDA+U) starting point bit below $n_f = 6 $. In the latter case the electronic specific heat coefficient $γ$ attains a smaller value in $γ$-Pu than in $α$-Pu, in contradiction to experiment, while in the former case our calculations reproduce the experimentally observed large increase of $γ$ in $δ$-Pu as compared to the $α$ phase. This enhancement of the electronic specific heat coefficient in $δ$-Pu is due to strong electronic correlations present in this phase, which cause a substantial increase of the electronic effective mass, and high density of states at $E_F$. The densities of states of $α$ and $δ$-plutonium obtained starting from the open-shell configuration are also in good agreement with the experimental photoemission spectra.