Schematic of the atomic orbital energy levels for Th, Pa, U, Np, Pu, Am, and the O2p band. The 5f orbital energy decreases steadily across the row, becoming nearly degenerate with the O2p band beginning with Pu. This leads to a metal-ligand mixing proportional to a Hamiltonian matrix element between the An5f and the O2p orbitals divided by the orbital energy difference. Although the matrix element decreases steadily across the row as the actinide 5f orbital contracts, it is offset by the energy denominator which becomes small for the later member of the row, leading to significant mixing and predictions of covalency in the calculations.
The fluorite crystal structure exhibited by AnO2, where An=Th, Pa, U, Np, Pu, and Am. O atoms = red balls, An atoms = green balls. The black arrows illustrate the (100) AFM ordering.
Left: The computed gap (HSE) versus the experimental gap of AnO2 (An=Th, Pa, U, Np, Pu, and Am). The dashed line has a slope of unity. Note the circle for PaO2 represents only a computed value, as we are not aware of an experimental result. Right: The computed lattice constant (HSE) versus the experimental lattice parameter for the AnO2 series.
The calculated density of states of AFM AnO2 (An=Th, Pa, U, Np, Pu, and Am) from the HSE approximation with spin-orbital coupling. The magnitudes of the gap in these figures are slightly from those in Table II.
Left: Correlation of experimental gap for AnO2 with computed gap from various approximations. Right: Correlation of experimental lattice constant with computed lattice constant from various approximations. We were unable to find lattice constants reported with DMFT.
Calculated relative energies for AFM and FM AnO2 (An=Th, Pa, U, Np, Pu, and Am) from HSE and HSE+SOC, respectively, as well the calculated AFM gap and magnetic moment.
Comparison of various approximations for the lattice constant (Å), band gap (eV), and insulator classification for AnO2 (An=Th, Pa, U, Np, Pu, and Am), as well as experiment.
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