Electron correlation and spin-orbit coupling effects in US3 and USe3

A systematic density functional theory (DFT)+U study is conducted to investigate the electron correlation and spin-orbit coupling (SOC) effects in US3 and USe3. Our calculations reveal that inclusion of the U term is essential to get energy band gaps for them, indicating the strong correlation effects for uranium 5f electrons. Taking consideration of the SOC effect results in small reduction on the electronic band gaps of US3 and USe3, but largely changes the energy band shapes around the Fermi energy. As a result, US3 has a direct band gap while USe3 has an indirect one. Our calculations predict that both US3 and USe3 are antiferromagnetic insulators, in agreement with corresponding experimental results. Based on our DFT+U calculations, we systematically present the ground-state electronic, mechanical, and Raman properties for US3 and USe3.Comment: 6 pages, 6 figure

Phylogeny and classification of the bamboos (Poaceae: Bambusoideae) based on molecular and morphological data

Chloroplast ndhF gene sequences and morphological and leaf anatomical characters were analyzed separately and as combined data sets to reconstruct the phylogeny of subfamily Bambusoideae. The analyses further confirmed that the monophyletic bambusoid clade consists of only two monophyletic lineages: the woody bamboos, and the herbaceous olyroid bamboos. Buergersiochloa was resolved as the basal lineage in the herbaceous olyroids, whereas Pariana/Eremitis was sister to the rest of the olyroids. The woody bamboos were divided into two main groups: temperate woody bamboos and tropical woody bamboos; and the tropical clade was further subdivided along geographic lines into the Old World woody bamboos and the New World woody bamboos. Puelia was resolved as the most basal lineage of the \u27higher grasses\u27 and thus was excluded from the bambusoid clade. Streptogyneae joined the oryzoids, including the Oryzeae and Ehrharteae, to form another separate monophyletic clade. The results of this study indicate that the current Bambusoideae is not acceptable phylogenetically. Therefore a new circumscription of the Bambusoideae with two tribes is proposed in which only members of the bambusoid clade are included; the woody bamboos are classifed as one tribe, the Bambuseae, and the herbaceous olyroid bamboos are classified in another tribe, the Olyreae;In order to provide additional resolution of phylogenetic relationships within the bambusoid clade, an attempt to generate nuclear ribosomal ITS sequence data of bamboos was made. However, polymerase chain reaction amplification (PCR) led to the recovery of fungal instead of bamboo sequences. Phylogenetic analyses based on the 5.8S sequences indicated that all the sequences belonged to basidiomycetes and that none was an ascomycete. A diverse assemblage of basidiomycetes was isolated from different bamboo hosts and various fungi coexisted in the same host plant. No evidence showed that closely related fungi were associated with closely related bamboo hosts. True bamboo ITS sequences were obtained only after leaf surface sterilization before DNA isolation. This study highlights the possibility of inadvertent PCR amplification of contaminating DNA in molecular phylogenetic studies. The results also indicate that a close ecological association between epiphytic basidiomycetes and bamboo leaves may exist, but further study is needed

First-principles calculations of phase transition, elasticity, and thermodynamic properties for TiZr alloy

tructural transformation, pressure dependent elasticity behaviors, phonon, and thermodynamic properties of the equiatomic TiZr alloy are investigated by using first-principles density-functional theory. Our calculated lattice parameters and equation of state for $\alpha$ and $\omega$ phases as well as the phase transition sequence of $\alpha$$\mathtt{\rightarrow}$$\omega$$\mathtt{\rightarrow}$$\beta$ are consistent well with experiments. Elastic constants of $\alpha$ and $\omega$ phases indicate that they are mechanically stable. For cubic $\beta$ phase, however, it is mechanically unstable at zero pressure and the critical pressure for its mechanical stability is predicted to equal to 2.19 GPa. We find that the moduli, elastic sound velocities, and Debye temperature all increase with pressure for three phases of TiZr alloy. The relatively large $B/G$ values illustrate that the TiZr alloy is rather ductile and its ductility is more predominant than that of element Zr, especially in $\beta$ phase. Elastic wave velocities and Debye temperature have abrupt increase behaviors upon the $\alpha$$\mathtt{\rightarrow}$$\omega$ transition at around 10 GPa and exhibit abrupt decrease feature upon the $\omega$$\mathtt{\rightarrow}$$\beta$ transition at higher pressure. Through Mulliken population analysis, we illustrate that the increase of the \emph{d}-band occupancy will stabilize the cubic $\beta$ phase. Phonon dispersions for three phases of TiZr alloy are firstly presented and the $\beta$ phase phonons clearly indicate its dynamically unstable nature under ambient condition. Thermodynamics of Gibbs free energy, entropy, and heat capacity are obtained by quasiharmonic approximation and Debye model.Comment: 9 pages, 10 figure

Magnetization in two-dimensional electron gas in a perpendicular magnetic field: the roles of edge states and spin-orbit coupling

We study the de Haas--van Alphen (dHvA) oscillations in the magnetization of a two-dimensional electron gas (2DEG) under the influence of the edge states and/or the Rashba spin-orbit interaction (SOI). The boundaries of the systems lift partially the degeneracies of Landau levels (LL's) and the resulting edge states lead to the changes of both the center and the amplitude of the sawtoothlike magnetization oscillation. The SOI mixes the spin-up and spin-down states of neighboring LL's into two unequally spaced energy branches. The inclusion of SOI changes the well-defined sawtooth pattern of the dHvA oscillations in the magnetization. The weaker the magnetic field is, the larger is the change of the dHvA oscillations due to the edge effect and/or the spin-orbit coupling. Some theoretical results are compared with the experimental data.Comment: 9 pages, 9 figure