Hybrid density functionals, which replaces a fraction of density functional theory (DFT) exchange with exact Hartree-Fock (HF) exchange, have been used to study the structural, magnetic, and electronic properties of delta-Plutonium. The fractions of exact Hartree-Fock exchange used were 25%, 40%, and 55%. Compared to the pure PBE functional, the lattice constants expanded with respect to the experimental value when the PBE-HF hybrid functionals were applied. A non-magnetic ground state was realized for 55% HF contribution; otherwise the ground state was anti-ferromagnetic. The 5f electrons tend to exhibit slight delocalization or itinerancy for the pure PBE functional and well-defined localization for the hybrid functionals, with the degree of 5f electron localization increasing with the amount of HF exchange. Overall, the performance of the hybrid density functionals do not seem superior to pure density functionals for delta-Plutonium.
Ab-initio relativistic dynamical mean-field theory is applied to resolve the long-standing controversy between theory and experiment in the "simple" face-centered cubic phase of plutonium called delta-Pu. In agreement with experiment, neither static nor dynamical magnetic moments are predicted. In addition, the quasiparticle density of states reproduces not only the peak close to the Fermi level, which explains the large coefficient of electronic specific heat, but also main 5f features observed in photoelectron spectroscopy.
Scalar-relativistic DFT-GGA has been used to study adsorption of water in molecular and dissociative configurations on delta-Plutonium (111) surface. In molecular state, water is physisorbed in an almost flat-lying orientation at a one-fold coordinated on-top site. The interaction of the water 1b1 orbital and the Pu-6d orbital provides the stability of water on the surface, implying that the Pu-5f electrons remain chemically inert. The co-adsorption cases of partially dissociated and fully dissociated products at the three-fold hollow sites yield chemisorption, coupled with rumpling of the sur…
We suggest a model for the magnetic dynamics of - plutonium and its alloys in order to show that the dynamical fluctuations of the magnetization density, or spin fluctuations, may be responsible for the anomalies of their observed thermal expansion. We show that due to strong magneto-elastic coupling, spin fluctuations may essentially contribute to the volume strain by giving a negative magneto-volume contribution that is proportional to the squared local magnetic moment and the magnetic Gruneisen constant which is negative in - plutonium. In the presented model, the local magnetic moment incr…
Adsorption of carbon, nitrogen, and oxygen on the (111) surface of delta-Plutonium has been studied within the framework of density functional theory using the full-potential linear augmented plane wave plus local basis (FP-LAPW+lo) method. All adatoms prefer to bind at the higher coordinated hollow sites, with the chemisorption energies for C, N, and O being 6.539 eV, 6.714 eV, and 8.2 eV respectively. The work function and the surface Pu magnetic moments respectively increased and decreased in all cases upon chemisorption. The partial charges inside the muffin tins spheres, difference charge…
The electronic and geometric properties of bulk fcc delta-plutonium and the quantum size effects in the surface energies and the work functions of the (001) ultra thin films (UTF) up to 7 layers have been investigated with periodic density functional theory calculations within the full-potential linearized augmented-plane wave (FP-LAPW) approach as implemented in the WIEN2k package. Our calculated equilibrium atomic volume of 178.3 a.u.^3 and bulk modulus of 24.9 GPa at the fully relativistic level of theory, i.e. spin-polarization and spin-orbit coupling included, are in good agreement with t…
By combining the local density approximation (LDA) with dynamical mean field theory (DMFT), we report a systematic analysis of the spectral properties of $δ$-plutonium with varying $5f$ occupancy. The LDA Hamiltonian is extracted from a tight-binding (TB) fit to full-potential linearized augmented plane-wave (FP-LAPW) calculations. The DMFT equations are solved by the exact quantum Monte Carlo (QMC) method and the Hubbard-I approximation. We have shown for the first time the strong sensitivity of the spectral properties to the $5f$ occupancy, which suggests using this occupancy as a fitting pa…
Nuclear Magnetic Resonance studies of Ga stabilized delta-Pu reveal detailed information about the local distortions surrounding the Ga impurities as well as provides information about the local spin fluctuations experienced by the Ga nuclei. The Ga NMR spectrum is inhomogeneously broadened by a distribution of local electric field gradients (EFGs), which indicates that the Ga experiences local distortions from cubic symmetry. The Knight shift and spin lattice relaxation rate indicate that the Ga is dominantly coupled to the Fermi surface via core polarization, and is inconsistent with magneti…
The Debye-Waller factor has been calculated for stabilized delta-phase plutonium with 5% aluminum. A quasi-harmonic Born-von Karman force model with temperature dependent phonon frequencies was used to calculate the mean-square thermal atomic displacement from absolute zero to 800 K. Implementation of the observed anomalous softening of the long wavelength phonons with increasing temperature cannot account for the softening of the measured thermal parameter at high temperatures nor for its rather high value at low temperatures. The implications for diffraction measurements on delta-phase stabi…
Many theories published in the last decade propose that either ordered or disordered local moments are present in elemental plutonium at low temperatures. We present new experimental data and review previous experimental results. None of the experiments provide any evidence for ordered or disordered magnetic moments (either static or dynamic) in plutonium at low temperatures, in either the alpha- or delta-phases. The experiments presented and discussed are magnetic susceptibility,electrical resistivity, NMR, specific heat, and both elastic and inelastic neutronscattering. Many recent calculati…
GICs doped with elements containing d and f orbitals have been studied rarely. We control the distribution and density of intercalated actinide metals (Th, U and Pu), and consider the effect of changing the distance of two adjacent carbon layers on the electronic structure so as to infer the physical properties of such materials under high pressure or high temperature - which is of great significance in fundamental research. According to band schemas, those GICs are all metallic. The projected density of states (PDOS) indicates that the metal atoms first undergo hybridization of its s, p, d, a…
The correlated band theory implemented as a combination of the local density approximation with the exact diagonalization of the Anderson impurity model is applied to PuO$_2$. We obtain an insulating electronic structure consistent with the experimental photoemission spectra. The calculations yield the band gap of 1.8 eV and a non-magnetic singlet ground state that is characterized by a non-integer filling of the plutonium $f$ shell ($n_f\approx 4.5$). Due to sizeable hybridization of the $f$ shell with the $p$ states of oxygen, the ground state is more complex than the four-electron Russell--…
The crystallographic and magnetic properties of La{0.5+delta}A{0.5-delta}Mn{0.5+epsilon}Ru{0.5-epsilon}O{3} (A= Ca, Sr, Ba) were investigated by means of neutron powder diffraction. All studied samples show the orthorhombic perovskite crystal structure, space group Pnma, with regular (Mn,Ru)O{6} octahedra and no chemical ordering of the Mn3+ and Ru4+ ions. Ferromagnetic spin structures were observed below Tc ~ 200-250 K, with an average ordered moment of ~ 1.8-2.0 Bohr magnetons per (Mn,Ru). The observation of long-range ferromagnetism and the absence of orbital ordering are rationalized in te…
FAPbI3, as a typical hybrid organic-inorganic perovskite, has attracted considerable interest due to its band gap suitable for visible light absorption and good thermal stability. A barrier to the use of FAPbI3 in commercial, stable devices is its unwanted black-to-yellow (non-perovskite to perovskite, commonly known as delta-to-alpha) phase transition at around 300 K. The intrinsic mechanisms of such phase transition are far from clear, being the detailed structural description for the alpha-phase still missing. By combined Density Functional Theory (DFT) calculations, lattice dynamics analys…
Oxygen molecule adsorptions on a Pu (100) surface have been studied in detail, using the generalized gradient approximation to density functional theory. Dissociative adsorption with a layer by layer alternate spin arrangement of the plutonium layer is found to be energetically more favorable compared to molecular adsorption. Hor2 approach on a bridge site without spin polarization was found to the highest chemisorbed site with energy of 8.787 eV among all the cases studied. The second highest chemisorption energy of 8.236 eV, is the spin-polarized Hor2 or Ver approach at center site. Inclusio…
We present a detailed comparison of the S0, S1 (n -> π*) and S2 (π-> π*) potential energy surfaces (PESs) of the prototypical molecular switch azobenzene as obtained by Delta-self-consistent-field (Delta-SCF) Density-Functional Theory (DFT), time-dependent DFT (TD-DFT) and approximate Coupled Cluster Singles and Doubles (RI-CC2). All three methods unanimously agree in terms of the PES topologies, which are furthermore fully consistent with existing experimental data concerning the photo-isomerization mechanism. In particular, sum-method corrected Delta-SCF and TD-DFT yield very similar results…
Time-resolved Kerr rotation measurements were performed in InGaAs/GaAs quantum wells nearby a doped Mn delta layer. Our magneto-optical results show a typical time evolution of the optically-oriented electron spin in the quantum well. Surprisingly, this is strongly affected by the Mn spins, resulting in an increase of the spin precession frequency in time. This increase is attributed to the variation in the effective magnetic field induced by the dynamical relaxation of the Mn spins. Two processes are observed during electron spin precession: a quasi-instantaneous alignment of the Mn spins wit…
In this work we present a systematic study of three representative iridium dyes, namely, Ir(ppy)3, FIrpic and PQIr, which are commonly used as sensitizers in organic optoelectronic devices. We show that electronic correlations play a crucial role in determining the excited-state energies in these systems, due to localization of electrons on Ir d orbitals. Electronic localization is captured by employing hybrid functionals within time-dependent density-functional theory (TDDFT) and with Hubbard-model corrections within the delta-SCF approach. The performance of both methods are studied comparat…
We present a modification of the $Δ$SCF method of calculating energies of excited states, in order to make it applicable to resonance calculations of molecules adsorbed on metal surfaces, where the molecular orbitals are highly hybridized. The $Δ$SCF approximation is a density functional method closely resembling standard density functional theory (DFT), the only difference being that in $Δ$SCF one or more electrons are placed in higher lying Kohn-Sham orbitals, instead of placing all electrons in the lowest possible orbitals as one does when calculating the ground state energy within standard…
