Review of the Structural Stability, Electronic and Magnetic Properties of Nonmetal-Doped TiO2_2 from First-Principles Calculations

This paper reviews and summarizes the recent first-principles theoretical studies of the structural stability, electronic structure, optical and magnetic properties of nonmetal-doped TiO$_2$. The first section presents a comparison study of the structural stability for X-anion and X-cation doped TiO$_2$ (X=B, C, Si, Ge, N, P, As, Sb, S, Se, Te, F, Cl, Br, and I), which reveals that the sites of nonmetal dopants (i.e., at O sites or at Ti sites) in TiO$_2$ are determined by the growth condition of doped TiO$_2$ and the dopants' electronegativities. The next section reviews the electronic structure, optical absorption and mechanism of the visible-light photocatalytic activity for nonmetal-doped TiO$_2$. The third section summarizes the origin of the spin-polarization and the magnetic coupling character in C- (N- and B-) doped TiO$_2$.Comment: 21 pages, 24 figures, 3 table

Multivariate Partial Distribution: A New Method of Pricing Group Assets and Analyzing the Risk for Hedging

Based on the Partial Distribution (Feng Dai, 2001), a new model to price an asset (MPA) is given. Going a step further, this paper puts forward the Multivariate Partial Distribution (MPD) for the first time. By use of MPD, we could gain a new kind of model for pricing the group assets (MPGA), in which the competition and cooperation are considered. Based on MPGA, the integrated risk of group assets can be divided to hedging risk and independent risk, and the corresponding models are given. So we could analyze the price risk of group assets in more particular way. The conclusions show that assets are hedged in simple way of one to one can not eliminates completely their market risk in many cases. So there should be an optimal ratio between underlying asset and its derivative in hedging. The approach to determine the optimal ratio in hedging is offered in this paper. By the MPA and MPGA, we also could interpret five of interesting economic propositions in analytic way.multivariate Partial Distribution; pricing assets; group assets; risk analysis; optimal hedging

Development Power and Its Power Model: The Analytic Approach for Continuous Motivity of Economic Growth

Based on the Partial Distribution [F. Dai, 2001] and the theory of Development Power [F. Dai, 2004], this paper discusses the power model of relation between development power (DP) and productivity. The power model also supports the hypothesis [F. Dai, 2005] that there are three kinds of energy states in economy, i.e. normal state, strong state and super state, and DP is the continuous motivity to economic growth. By the power model of DP, we could interpret in analytic way that the diffusion of DP and the diversifications of economic development also might be occurred after the super state. Finally, the conclusions in this paper are researched in the empirical way, the results indicate the power model is better than the exponential model of DP in many cases, and we could get the inimitable outcomes in describing the macroeconomic process by the power model of DP.Development Power (DP), Partial Distribution, power model, macroeconomic analysis

Multivariate Partial Distribution: A New Method of Pricing Group Assets and Analyzing the Risk for Hedging

Based on the Partial Distribution (Feng Dai, 2001), a new model to price an asset (MPA) is given. Going a step further, this paper puts forward the Multivariate Partial Distribution (MPD) for the first time. By use of MPD, we could gain a new kind of model for pricing the group assets (MPGA), in which the competition and cooperation are considered. Based on MPGA, the integrated risk of group assets can be divided to hedging risk and independent risk, and the corresponding models are given. So we could analyze the price risk of group assets in more particular way. The conclusions show that assets are hedged in simple way of one to one can not eliminates completely their market risk in many cases. So there should be an optimal ratio between underlying asset and its derivative in hedging. The approach to determine the optimal ratio in hedging is offered in this paper. By the MPA and MPGA, we also could interpret five of interesting economic propositions in analytic way.Multivariate Partial Distribution pricing assets group assets risk analysis optimal hedging

Discovery of a two-dimensional topological insulator in SiTe

Two-dimensional (2D) topological insulators (TIs), a new state of quantum matter, are promising for achieving the low-power-consuming electronic devices owning to the remarkable robustness of their conducting edge states against backscattering. Currently, the major challenge to further studies and possible applications is the lack of suitable materials, which should be with high feasibility of fabrication and sizeable nontrivial gaps. Here, we demonstrate through first-principles calculations that SiTe 2D crystal is a promising 2D TI with a sizeable nontrivial gap of 0.220 eV. This material is dynamically and thermally stable. Most importantly, it could be easily exfoliated from its three-dimensional superlattice due to the weakly bonded layered structure. Moreover, strain engineering can effectively control its nontrivial gap and even induce a topological phase transition. Our results provide a realistic candidate for experimental explorations and potential applications of 2D TIs

Density functional characterization of the antiferromagnetism in oxygen-deficient anatase and rutile TiO2

We present theoretical evidence for local magnetic moments on Ti3+ ions in oxygen-deficient anatase and rutile TiO2 observed in a recent experiment [S. Zhou, et al., Phys. Rev. B 79, 113201 (2009)]. Results of our first-principles GGA+U calculations reveal that an oxygen vacancy converts two Ti4+ ions to two Ti3+ ions in anatase phase, which results in a local magnetic moment of 1.0 $\mu_B$ per Ti3+. The two Ti3+ ions, however, form a stable antiferromagnetic state, and similar antiferromagnetism is also observed in oxygen-deficient rutile phase TiO2. The calculated results are in good agreement with the experimentally observed antiferromagnetic-like behavior in oxygen-deficient Ti-O systems.Comment: 16 pages, 5 figure