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A model is presented to calculate the stopping power of ions propagating in dense matter. Comparisons with experiment in the cold dense regime are presented and discussed. Further, we present results from the warm dense matter regime and the field of high energy density physics.

The electrical anomaly observed in the high-temperature phase of magnetite under pressure is studied in the framework of DFT/LSDA+U formalism. We show that the phenomenon cannot be accounted for by a coordination crossover nor by a Fe 2 + high-spin (HS) to an intermediate-spin (IS) transition. We suggest the transition may be related to the formation of an inhomogeneous mixed-spin state system HS → HS / LS with cations in octahedral sites.

Ab initio calculations (VASP) are performed on hydrogen containing Fe 4 N : Fe 4 NH n , n = 0 , 1 , 2 , 3 . Effects of hydrogen on structural and magnetic properties are pointed out. For n = 3 the calculated magnetization (177 emu/g) is close to the experimental value obtained from oxalate precursors in fluidized bed reactors. From this result, we show some drawbacks of this solid state method of synthesis for Fe 4 N magnetic particles.

We show that thermodynamic properties of Pu metal as well as those of Pu (1− x ) M x (M = Al, Ga, In) compounds are poorly described by traditional DFT but rather well modeled when including magnetic interactions. The cluster variation method is used to emphasize that the presence of Ga atoms in the δ-Pu phase leads to an important chemical short-range order which stabilizes this phase as a function of temperature and composition. Our results indicate also that Ga atoms introduce local strain fields in δ phase which relax with increasing distance from the Ga atoms. Finally we show that local relaxations are also essential to predict correct vacancy formation and migration energies in this phase.

The defect population is important for understanding the microstructure of δ-plutonium. Using spin-polarized density-functional theory, we calculate the formation energies of monovacancies as well as divacancies. We show that the unrelaxed values are quite independent of the magnetic configuration while atomic relaxations lead to smaller values, relaxation effects being larger for the disordered magnetic structure.

We present results on the structural stability of Pu1− x Ga x alloys based on the local spin-density approximation and including non-local corrections to the exchange–correlation functional (generalized gradient approximation). First, we used both the linearized augmented plane-wave and the projector augmented wave (PAW) methods to calculate the energies of formation of five intermediate phases which occur in the Pu–Ga phase diagram. Then, PAW calculations were performed for various superstructures based on the fcc lattice to get the interaction parameters to describe the energetics of the δ-Pu–Ga solid solution. To discuss the effects of the chemical short-range order on the structural stability of the δ-Pu–Ga solid solution as a function of temperature, the cluster variation method configurational entropy has been introduced using the regular tetrahedron approximation. The solid part of the Pu-rich side of the phase diagram involving phase equilibria between the Pu phases, the δ-Pu–Ga solid solution and...

The formation energies of Pu–X (X = Al, Ga, In) compounds are calculated in the framework of density functional theory within the local spin-density approximation and non-local corrections to the exchange-correlation functional. The factors that govern the stability of δ-(Pu–X) solid solutions are analysed using fcc superstructures for which total energy calculations are performed. The cluster variation method is used to determine the influence of chemical short range order on the structural stability of δ-(Pu–X) solid solutions as a function of temperature and composition. The differences between the three systems are discussed. The calculated Pu–X (X = Al, Ga, In) phase diagrams in the Pu-rich side are compared with the experimental ones.

In the framework of density functional theory and the generalized gradient approximation, we investigate the effects of magnetism on four plutonium allotropes. We show that an antiferromagnetic configuration gives a structural hierarchy which is consistent with experimental features. Using a simple Debye–Gruneisen model and a corrective term, we are able to draw a P–T phase diagram of Pu. Harmonic contributions are not sufficient for obtaining a correct description of the thermal properties of Pu and we emphasize the important role played by electronic and anharmonic contributions.

Equilibrium properties for the -phase of Pu have been calculated. Taking into account strong electron correlations in the 5f shell, we show how the equilibrium volume and the bulk modulus are improved in comparison to previous results using the local density approximation (LDA) or the generalized gradient approximation (GGA). In addition, an augmentation of the orbital moment is observed following Hund's rules, reducing the total magnetic moment. The stability of the -phase is explored and for the first time a positive value for the tetragonal shear constant is found.

The electronic and magnetic structures of the perovskite CaMnO 3 are self-consistently calculated assuming two crystal structures at the same formula unit volume within the local spin density functional theory and the augmented spherical wave (ASW) method. From the comparisons of energy differences between the different magnetic states the ground state configuration is an insulator with G-type ordering. This result together with the magnitudes of the magnetic moments are in agreement with experiment. The influence of mixing between Mn and O is found spin dependent from the analysis of the crystal orbital overlap population (COOP) which enable to describe the chemical bond. The calculations underline a feature of a half metallic ferromagnet which could be connected with the colossal magnetoresistance (CMR) property of related compounds.

Electronic and magnetic properties of the double perovskites La 2 TIrO 6 (T=Mn, Fe, Co) are calculated ab initio and compared with experimental results. Using a self-consistent band-structure method within the local spin-density approximation (LSDA) total-energy and density-of-states (DOS) calculations are performed of ferromagnetic and antiferromagnetic spin configurations. Finally, we discuss the effect of ordering among the T and Ir sites by comparing two differently ordered structures.

We present the results of first-principles electronic-structure calculations for the molecule-based cyanide high-Curie-temperature magnetic insulators $\mathrm{Cs}M[{\mathrm{Cr}(\mathrm{CN})}_{6}],$ $M=\mathrm{Mn},$ Ni. The calculations are based on density-functional theory and the local-density approximation and employ the augmented-spherical-waves method. The electronic properties are found to be dominated by transition-metal $3d$ and ligand $2p$ orbitals. The chemical bonding is analyzed via an ab initio calculation of the crystal orbital overlap population (COOP). The magnetic properties are explained by the orthogonality/overlap of magnetically active orbitals as studied by the COOP. Possible pathways for the exchange interaction are identified. In particular the sign of the exchange integrals between different effective magnetic sites is deduced. Excellent agreement with experimental data is found. While proving essential for the consistent understanding of electronic, magnetic, and chemical properties of these materials our first-principles approach moreover allows for the prediction as well as the deeper understanding of the type of long-range magnetic order. Thereby it goes beyond the conclusions usually drawn from Goodenough-Kanamori superexchange rules or the model by Kahn and Briat.

Band structure calculations using the spin-polarized ASW method were performed on the title compounds. Nonmetallic behavior is attributed to spin-polarization-induced opening of a gap at the Fermi level. Curie temperatures were calculated and found to be in reasonable agreement with the real evolution of silicon and germanium derivatives.

A method is presented to calculate ab initio exchange constants and spin-wave excitations of multi-sublattice magnetic structures on the basis of total-energy calculations of incommensurate magnetic structures. Here the exchange energies, dispersion curves and Curie temperature for magnetite (Fe3O4) are obtained and compared with experimental results.

Using a simple approach of ferromagnetic interactions through a 180° superexchange in a perovskite lattice a composition has been set-tip : La2MnIrO6. A band-structure calculation having confirmed such a simple approach, the compound was prepared and characterized. Structural and magnetic studies have confirmed the ferromagnetic behaviour of such an oxide. This methodology is now used to define a new class of ferromagnetic oxides.

Self-consistent band structure calculations within the local spin density approximation (LSDA) were carried out for CrN in the cubic (B1) and in the orthorhombic structures. Nonmagnetic (NSP), ferromagnetic (F) as well as antiferromagnetic (AF) ground states were assumed. Within the experimentally observed orthorhombic structure of CrN (TN = 273 K) our results show a descending order of the ground state energies: NSP > F > AF. Further stabilization of the AF configuration is achieved when spins compensate within one plane, yielding a moment of 2.44μB carried by chromium, which is in good agreement with experiment.

A methodology is reported for defining a class of ferromagnetic oxides, based on theoretical and experimental considerations. Starting from phenomenological superexchange theory, a perovskite oxide with composition La2MnIrO6 was proposed to order ferromagnetically. Self‐consistent band‐structure calculations are used to check the magnetic order and the synthesis and characterization subsequently followed. An agreement between theoretical and experimental results was found.

The magnetic properties of the ferromagnetic nitride Fe3N were investigated by means of the ASW method where the spin-orbit coupling enters the variational part of the self-consistent loop. The calculations of magnetocrystalline anisotropy energy were done for different values of the angle between magnetization and the c axis of the hexagonal structure. The easy axis of magnetization was found along this c axis. A least-square fit of the results allowed us to determine the relative contributions of first and second order anisotropy constants.

The electronic and magnetic properties of the ferromagnetic nitride Fe3N were investigated by use of the ASW method. The calculations were done in two different crystal structures : the experimental-hexagonal one and a hypothetical Cu3Au-type one- in order to correlate the magnetic structure of Fe3N with that of its homologues Fe3X (X = non-metal). Results were assessed in connection with existing experimental data (magnetic measurements, Mössbauer resonance). Independently of the structure, densities of states due to the iron-nitrogen bond are introduced at Fermi level and should play a role in the magnetism of the nitride.

In this study the influence of rare earth dopants in the surface oxide layer on the magnetic properties of iron nitride particles is investigated.

A comparative study of the band structure on the basis of local spin-density functional theory is presented for the ferrites Fe 3 O 4 , CoFe 2 O 4 , NiFe 2 O 4 , MnFe 2 O 4 and ZnFe 2 O 4 . The saturation magnetization is obtained and the trend of the calculated magnetic moments is interpreted and compared with experimental values.

The equation of state of $\ensuremath{\alpha}$- and $\ensuremath{\beta}$-boron have been studied by means of density-functional theory-generalized gradient approximation-projector-augmented wave (ABINIT) calculations up to 300 GPa. No distortion is observed in the $\ensuremath{\alpha}$ phase. Two structures have been considered for the $\ensuremath{\beta}$ phase: the classical $\ensuremath{\beta}\text{\ensuremath{-}}105$ as well as the recently proposed $\ensuremath{\beta}\text{\ensuremath{-}}106$ structure. The free-energy differences between these two structures are very small but their evolution under pressure are quite different. The $\ensuremath{\beta}\text{\ensuremath{-}}106$ structure is in better agreement with experiment by having an insulator/metal transition and a pressure-induced destabilization of the structure that could lead to an amorphization.

Mossbauer resonance studies on Mn-substituted Fe4N show that manganese occupies statistically both iron sites in the lattice. Replacement of Fe by Mn modifies the crystal growth process of Fe4N magnetic particles and leads to improvement of the extrinsic magnetic properties, i.e., Hc and σ r σ s , required for magnetic recording applications.

We present results on the structural stability of ${\mathrm{Pu}}_{(1\ensuremath{-}x)}{M}_{x}$ $(M=\mathrm{A}\mathrm{l},\mathrm{G}\mathrm{a},\mathrm{I}\mathrm{n})$ compounds in the framework of density functional theory within the local density approximation and generalized gradient approximation (GGA). An all-electron linear augmented plane wave method, which includes an additional ${p}_{1/2}$ local orbital in spin orbit coupling, is used in order to determine the formation energy of these compounds. Using the GGA and spin polarized calculations, the calculated structural hierarchy is in agreement with the trends observed in the experimental phases diagrams. The stability of the Pu-M compounds can be related to a strong pdf hybridization.

Due to its high saturation magnetization ( sigma /sub s/(0K) approximately=208 emu/g) and to the ease of obtaining it as a particulate material, Fe/sub 4/N could be a suitable magnetic material for replacing highly reactive metallic iron pigments ( sigma /sub s/(0K) approximately=218 emu/g) in high-density recording. Throughout a nitriding process of properly selected precursors Fe/sub 4/N can be obtained in either of two morphologies: acicular or isotropic. Further protection of the magnetic particles can be ensured through coating of the precursor particles prior to thermal decomposition in NH/sub 3//H/sub 2/ atmosphere or through substitutions with selected elements. The obtained passivated nitrides are characterized by high magnetic properties (H/sub c/ approximately=600 Oe; sigma /sub s/ approximately=150 emu/g) and chemical stability well adapted for use as magnetic pigments for high-density recording. >

The aim of this paper is to provide experimental data on various expanded elements in the warm dense matter regime. The experiments were done on the experimental facility “enceinte a plasma isochore” and are evaluated through a thorough comparison with ab initio calculations, average-atom codes, and chemical models. This comparison allows for the evaluation of the experimental temperatures that are not accessible to the measurements and permits the building of useful data tables gathering energy, pressure, conductivity, and temperatures. We summarize experiments performed on aluminum (0.1 and 0.3 g/cm3), nickel (0.2 g/cm3), titanium (0.1 g/cm3), copper (0.3 and 0.5 g/cm3), silver (0.43 g/cm3), gold (0.5 g/cm3), boron (0.094 g/cm3), and silicon (0.21 g/cm3) for temperatures ranging from 0.5 eV to 3-4 eV.

A band-structure calculation, (ASW method) on CuCr/sub 2/S/sub 4/ in order to determine its electronic and magnetic properties is reported. Local magnetic moments are calculated and compared with experimental values. A magnetic moment of 5.04 mu /sub B/ is found on chromium. Density of states shows the p-like character of the conductivity and allows the suggestion of an ionic model for the compound with two valence states for chromium. >

The synthesis of molecular-based magnets with high Curie temperatures is a challenge for chemists. Within the framework of first-principles methods (the ASW method) we study two well-characterized compounds in the hexacyanochromate (III) family: CsNi[Cr(CN) 6 ] and CsMn[Cr(CN) 6 ].

The presence of a rare earth (Ln) in a coating layer at the surface of iron nitride particles leads to an enhancement of their coercivity for Ln amounts as low as 2.5%. Results are interpreted on the basis of exchange anisotropy at the interface between LnFeO 3 layers formed at the surface of the Fe 4 N crystallites and the bulk at low Ln content and on shape effects of the particles at higher Ln. contents.

The electronic and magnetic structure of the ferrimagnetic nitride Mn4N was calculated as a function of lattice spacing by use of the ASW method. The magnetization is found to increase with decreasing lattice volume: ifdLn M/dP = 0.0017 kbar-1. This result is in agreement with previous NMR measurements on Mn4N under pressure.

Using the augmented spherical wave method (A. S. W.) we calculate the electronic and magnetic structures of Fe 4 N and Mn 4 N. Both nitrides are found to order magnetically exhibiting ferro- and ferrimagnetic spin alignment respectively. The magnetic moments found are in good agreement with neutron data. Both systems can be described via covalent magnetism. Comparison with Goodenough's phenomenological model as well as with Heusler alloys is given Calcul des structures electroniques et magnetiques en utilisant la methode de «l'onde spherique augmentee». Les deux composes s'ordonnent magnetiquement avec un alignement ferro- et ferrimagnetique. Les valeurs des moments magnetiques sont en bon accord avec celles de la litterature. Comparaison avec le modele phenomenologique de Goodenough et avec les alliages de Heusler