Irradiated Solids Laboratory

The Kohn-Sham system is the prototypical example of an auxiliary system that targets, in principle exactly, an observable like the electronic density without the need to calculate the complicated many-body wavefunction. Although the Kohn-Sham system does not describe excited-state properties directly, it also represents a very successful strategy guideline for many spectroscopy applications. Here we propose a generalization of the Kohn-Sham idea. In many situations one is interested only in limited answers to specific questions, whereas in state-of-the-art approaches a lot of information is generally calculated that is not needed for the interpretation of experimental spectra. For example, when the target is a spectrum S(ω) like the optical absorption of a solid, within time-dependent density-functional theory (TDDFT) one calculates the whole response function χ(r,r',ω). Analogously, within many-body perturbation theory (MBPT) one calculates the whole one-particle Green's function G(r,r',ω), while only the total spectral function A(ω) is needed for angle-integrated photoemission spectra. In this contribution, we advocate the possibility of designing auxiliary systems with effective potentials or kernels that target only the specific spectral properties of interest and are simpler than the self-energy of MBPT or the exchange-correlation kernel of TDDFT. In particular, we discuss the fundamentals and prototypical applications of simplified effective kernels for optical absorption and spectral potentials for photoemission, and we discuss how to express these potentials or kernels as functionals of the density.

The many-body problem cannot in general be solved exactly, and one of the most prominent approximations is to build perturbation expansions. A huge variety of expansions are possible, which differ by the quantity to be expanded, the expansion variable, the starting point, and ideas of how to re-sum or terminate the series. Although much has been discussed and much has been done, some choices were made for historical reasons, in particular, limited computation or storage capacities. The present work aims to examine the justification for different choices made in different contexts, by comparing the components of functionals based on Green's functions on the one side, and on the charge density on the other side. Of particular interest will be the question of how to build an optimal starting point for the approximation of non-local quantities, making use of near- or far-sightedness, and daring to consider models beyond the homogeneous electron gas. This will include the use of connector approximations. We will also discuss why it is a good idea to build functionals of the density.

In article number 1902941, Alessandro Chiolerio and co-workers describe, the converse piezo-electro-kinetic (CPEK) effect, which is a nonequilibrium electric-field-driven surface atom drift able to introduce structural anisotropy on former spherical metallic nanoparticles, resulting in an elongation of the whole nanocomposite hundred-fold times the electrostriction effect.

The phase diagram of boron carbide is calculated within the density functional theory as a function of temperature and pressure up to 80 GPa, accounting for icosahedral, graphitelike, and diamondlike atomic structures. Only some icosahedral phases turn out to be thermodynamically stable with atomic carbon concentrations (c) of 8.7% (B10.5C), 13.0% (B6.7C), 20% (B4C), and 28.6% (B2.5C), respectively. Their respective ranges of stability under pressure and temperature are calculated, and the theoretical T-P-c phase diagram boundaries are discussed. At ambient conditions, the introduction in the phase diagram of the new phase B10.5C with an ordered crystalline motif of 414 atoms is shown to bring the theoretical solubility range of carbon in boron close to the experimental one. The link with the experimental phase diagram consisting of one single phase having the R3¯m space group is discussed, and the concept of partial occupation of Wyckoff’s site is introduced. At high pressure, the phase diagram is defined by a new carbon-rich phase B2.5C, which is stabilized by both pressure and temperature in our calculations. All of the other diamond and graphite phases reported previously turn out to be thermodynamically unstable in our calculations, although some of them are observed in high pressure experiments.

Abstract Aluminium is a fairly recent metal (XIXth century). Investigations of its alloys developed in a military-industrial context. Duralumin was, thus, discovered at the beginning of the last century in Prussian Germany by the Metallurgist Engineer Alfred Wilm (1869 – 1937) who had been explicitly mandated to look for an improved aluminium alloy in a military-owned research centre located in Neubabelsberg, just south-west of Berlin. The name Duralumin is as much due to the fact that it is hard as to the fact it has first been industrially produced in Duren. International connections, as well as harsh competition, accompanied the first research on this alloy in the beginning of the twentieth century.

Abstract To understand the influence of proton irradiation on lattice‐matched GaInP/GaAs/Ge triple junction (TJ) solar cells under low intensity, low temperature (LILT) conditions, we investigated electrical behaviors of top, middle, and bottom component cells together with TJ cells under these conditions. Proton irradiations with energies of 1 MeV and fluences ranging from 2 × 1010 to 1.6 × 1012 cm−2 were performed at temperatures ranging from 100 to 300 K. Our study reveals that any of the 3 subcells can become the current limiting cell in the TJ cell, depending on temperature and fluence. In particular, remarkable degradation of the bottom cell at low temperature can make this subcell the current limiting in a TJ cell even for limited fluences. The results indicate that the defect distribution is non‐uniform for low temperature irradiation.

In core‐level photoelectron diffraction, the surface atomic structure is imaged through a local source wave. In valence photoemission, the source wave gets effectively localized at a core‐valence resonance, and local information on valence states can be obtained. Through photoelectron diffraction at the Ti 2 p − 3 d resonance, we have determined the charge distribution of the gap state at n ‐doped TiO 2 surfaces. Second, the origin of spin polarization in resonant photoemission from non‐ferromagnetic surfaces is critically reviewed. We have developed a multiple scattering computational method for resonant photoemission and have applied it to Cr(110) and Fe(100). For circular polarized light, we find that the resonant photocurrent is strongly spin polarized in antiferromagnets and disordered ferromagnets, in agreement with experiment. Contrary to previous interpretations, we show that this spin polarization is essentially unrelated to local magnetic moments, but because of an angular momentum transfer from the photon to the photoelectron via core spin‐orbit coupling and exchange autoionization decay. Copyright © 2016 John Wiley & Sons, Ltd.

The aim of this study was to better understand the incorporation of rare‐earth elements in glass‐ceramics of nuclear interest. We synthesized glass‐ceramics from glasses in the system SiO2–B2O3–Na2O–CaO–Al2O3–MoO3–Gd2O3 by various heat treatments. Gadolinium is used both as a spectroscopic probe and as a minor actinide surrogate. Glass‐ceramics contain only one crystalline phase in the bulk: powellite (CaMoO4). This phase can incorporate Gd3+ and Na+ ions by substitutions on the Ca site. We demonstrated that the charge compensation by Na+ favors the incorporation of rare‐earth elements. Moreover, the incorporated elements do not seem to be randomly distributed into the powellite structure.

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