To build on the success of other mineral systems employed in solar cells, including kesterites (Cu 2 ZnSnS 4 ) and herzenbergite (SnS), as well as mineral-inspired systems such as lead halide ...perovskites (CH 3 NH 3 PbI 3 ), we have searched for photoactive minerals with the additional constraint that a polar crystal structure is adopted. Macroscopic electric fields provide a driving force to separate electrons and holes in semiconductor devices, while spontaneous lattice polarisation in polar semiconductors can facilitate microscopic photo-carrier separation to enhance carrier stability and lifetimes. We identify enargite (Cu 3 AsS 4 ), stephanite (Ag 5 SbS 4 ), and bournonite (CuPbSbS 3 ) as candidate materials and explore their chemical bonding and physical properties using a first-principles quantum mechanical approach.
Solving the electronic structure from a generalized or standard eigenproblem is often the bottleneck in large scale calculations based on Kohn-Sham density-functional theory. This problem must be ...addressed by essentially all current electronic structure codes, based on similar matrix expressions, and by high-performance computation. We here present a unified software interface, ELSI, to access different strategies that address the Kohn-Sham eigenvalue problem. Currently supported algorithms include the dense generalized eigensolver library ELPA, the orbital minimization method implemented in libOMM, and the pole expansion and selected inversion (PEXSI) approach with lower computational complexity for semilocal density functionals. The ELSI interface aims to simplify the implementation and optimal use of the different strategies, by offering (a) a unified software framework designed for the electronic structure solvers in Kohn-Sham density-functional theory; (b) reasonable default parameters for a chosen solver; (c) automatic conversion between input and internal working matrix formats, and in the future (d) recommendation of the optimal solver depending on the specific problem. As a result, comparative benchmarks are shown for system sizes up to 11,520 atoms (172,800 basis functions) on distributed memory supercomputing architectures.
The structural variety of the alums is reviewed. Structure-spectra relationships are exemplified by the
2E
g−
4A
g phosphorescence of chromium alums and chromium-doped aluminium alums. The importance ...of exchange coupling between chromium ions in neat and diluted crystals is demonstrated by the concentration dependence of the phosphorescence properties. Structural phase transitions were observed in alums containing the monovalent cations Na
+, NH
4
+, K
+ and Tl
+, but not Rb
+ and Cs
+. The phosphorescence of the ammonium alum is presented in more detail.
Boron Carbide exhibits a broad composition range, implying a degree of intrinsic substitutional disorder. While the observed phase has rhombohedral symmetry (space group R3(bar)m), the enthalpy ...minimizing structure has lower, monoclinic, symmetry (space group Cm). The crystallographic primitive cell consists of a 12-atom icosahedron placed at the vertex of a rhombohedral lattice, together with a 3-atom chain along the 3-fold axis. In the limit of high carbon content, approaching 20% carbon, the icosahedra are usually of type B11Cp, where the p indicates the carbon resides on a polar site, while the chains are of type C-B-C. We establish an atomic interaction model for this composition limit, fit to density functional theory total energies, that allows us to investigate the substitutional disorder using Monte Carlo simulations augmented by multiple histogram analysis. We find that the low temperature monoclinic Cm structure disorders through a pair of phase transitions, first via a 3-state Potts-like transition to space group R3m, then via an Ising-like transition to the experimentally observed R3(bar)m symmetry. The R3m and Cm phases are electrically polarized, while the high temperature R3(bar)m phase is nonpolar.
During the analysis of the La (SS-B) autoantigen for catalytic activities an ATP-dependent doublestranded RNA unwinding activity was detected. Both native and recombinant La proteins from different ...species displayed this activity, which could be inhibited by monospecific anti-La antibodies. La protein was able to melt dsRNA substrates with either two 3′-overhangs or a single 3′- and a 5′-overhang. Double-stranded RNAs with two 5′-overhangs were not unwound, indicating that at least one 3′-overhang is required for unwinding. Sequence elements of the La protein that might be involved in dsRNA unwinding, such as an evolutionarily conserved putative ATP-binding motif and an element that is homologous to the double-stranded RNA binding protein kinase PKR, are discussed.
We are interested in the average behavior of interior-point methods (IPMs) for linear programming problems (LPs). We use the rotation-symmetry-model as the probabilistic model for the average case ...analysis. This model had been used by Borgwardt in his average case analysis of the simplex-method. IPMs solve LPs in three phases. First, one has to find an appropriate starting point, then a sequence of interior points is generated, which converges to the optimal face. Finally, the optimum has to be calculated, as it is not an interior point. We present upper bounds on the average number of iterations in the first and the third phase by looking at random figures of the underlying polyhedron. These bounds show, that IPMs solve LPs in strongly polynomial time in the average case, so only the dimension parameters and not the encoding length of the problem determine the average behavior of IPMs.
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