[en] Ab initio calculations (VASP) are performed on hydrogen containing Fe₄N:Fe₄NH_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 Fe₄N magnetic particles.

[en] DTPA (diethylene-triamino-pentaacetic acid) is a key molecule today because it is used as either a de-corporating agent at an industrial scale or a model molecule of amino-poly-carboxylic at a laboratory scale. Quantum molecular dynamics calculations have been performed on DTPA to better understand its behaviour towards actinides and more specifically plutonium. A series of computations have been made with the ABINIT code on an isolated PuDTPA ion at T=0 K and T=298 K as well as on its protonation: Pu(H)DTPA. The resulting structure of the PuDTPA complex appears to be circular with the ligand wrapped around the Pu atom almost completely. 2 types of Pu-C chemical bonds have been observed: ones where C is linked to N through 9 bonds (3.46 Angstroms) and those where C is linked to O through 5 bonds (3.31 Angstroms). 2 types of Pu-O bond (2.25 and 4.45 Angstroms) and 1 type of Pu-N bond (2.67 Angstroms) have also been observed. These results have allowed us to understand better the X-ray diffraction schemes obtained at ESRF synchrotron

[en] The determination of equations of states of heavy metals through ab initio calculation, i.e. without any adjustable parameter, allows to access to pressure and temperature thermodynamic conditions sometimes inaccessible to experiment. To perform such calculations, density functional theory (DFT) is a good starting point: when electronic densities are homogeneous enough, the local density approximation (LDA) remarkably accounts for thermodynamic properties of heavy metals, such as tantalum, or the light actinides, as well for static properties - equilibrium volume, elastic constants - as for dynamical quantities like phonon spectra. For heavier elements, like neptunium or plutonium, relativistic effects and strong electronic interactions must be taken into account, which requires more sophisticated theoretical approaches. (authors)

[en] Although thermodynamics of An(IV)DTPA (DTPA = diethylenetriaminepentaacetic acid) complexation have been reported for 50 years, reliable data at low ionic strength is still missing. Owing to the use of capillary electrophoresis coupled with an inductively coupled plasma mass spectrometer, it is possible to simultaneously detect at ultra-trace level all An(IV)DTPA species in various conditions (concentration of ligand, pH) and to determine the formation constants. New values were obtained for tetravalent actinides with DTPA as well as with nitrilotriacetate (NTA) used as a competitor. Besides, the formation constants of hydrolyzed An(OH)DTPA^2- species (An = Np, Pu) were also obtained for the first time using the variation of electrophoretic mobility as a function of pH at a constant DTPA concentration. The use of these data in radio toxicology indicates that two stable species, namely PuDTPA^- and Pu(OH)DTPA^2- are present at approximately the same concentration in blood. From ab initio molecular dynamic (AIMD), the metal-oxygen distances d(An-O) were calculated, and a linear relation was shown between d(An-O) and the formation constants. The interpolation of data allowed determination of K values along the tetravalent actinide series, e.g. K(NpDTPA), K(PaDTPA^-) and K(U(OH)DTPA^2-). (authors)

[en] Electronic and magnetic properties of the double perovskites La₂TIrO₆ (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. (orig.)

[en] 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[. (orig.)

[en] The combined evolution of the electronic structure softwares and computational capabilities makes quantum molecular dynamics simulations available for increasingly complex systems, up to several hundred atoms. Among the various ab initio techniques, Density Functional Theory (DFT) is very successful due to its important computational efficiency with respect to Hartree-Fock type approaches. Its combination with empirical treatments of the weak van der Waals interactions allows the simulation of equilibrium or dynamics properties of numerous systems of interest for the nuclear and defense industry. We present 3 direct applications of quantum molecular dynamics: the determination of the structure of the complex Pu(DTPA) ion where DTPA means diethylen-triamine-penta-acid, the calculation of the equation of state and the Hugoniot curve of TATB monocrystal. (authors)

[en] 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, Moessbauer 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. (orig.)

[en] In the case of an accidental nuclear event, contamination of human bodies by actinide elements may occur. Such elements have the particularity to exhibit both radiological and chemical toxicities that may induce severe damages at several levels, depending on the biokinetics of the element. In order to eliminate the actinide elements before they are stored in target organs (liver, kidneys, or bone, depending on the element), sequestering agents must be quickly injected. However, to date, there is still no ideal sequestering agent, despite the recent interest in this topic due to contamination concerns. DTPA (diethylene triamine pentaacetic acid) is currently generating interest for the development of oral or alternative self-administrable forms. Although biokinetics data are mostly available, molecular scale characterization of actinide-DTPA complexes is still scarce. Nevertheless, strong interest is growing in the characterization of An^IVDTPA^- complexes at the molecular level because this opens the way for predicting the stability constants of unknown systems or even for developing new analytical strategies aimed at better and more selective decorporation. For this purpose, Extended X-ray Absorption Fine Structure (EXAFS) and Ab Initio Molecular Dynamics (AIMD) investigations were undertaken and compared with capillary electrophoresis (CE) used in a very unusual way. Indeed, it is commonly believed that CE is incapable of extracting structural information. In capillary electrophoresis, the electrophoretic mobility of an ion is a function of its charge and size. Despite very similar zr ratios, partial separations between An^IVDTPA^- species (An^IV = Th, U, Np, Pu) were obtained. A linear relationship between the electrophoretic mobility and the actinide - oxygen distance calculated by AIMD was evidenced. As an example, the interpolated U-O distances in U^IVDTPA^- from CE-ICPMS experiments, EXAFS, AIMD, and the relationship between the stability constants and the ratio z/d_An-O, are all in agreement. This results in the capability to evaluate the stability constants for the formation of Pa^IVDTPA^-, Am^IVDTPA^- or Bk^IVDTPA^-. (authors)

[en] 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