First-Principles Study on Mechanical and Optical Behavior of Plutonium Oxide under Typical Structural Phases and Vacancy Defects.

The chemical corrosion aging of plutonium is a very important topic. It is easy to be corroded and produces oxidation products of various valence states because of its 5f electron orbit between local and non-local. On the one hand, the phase diagram of plutonium and oxygen is complex, so there is still not enough research on typical structural phases. On the other hand, most of the studies on plutonium oxide focus on PuO2 and Pu2O3 with stoichiometric ratio, while the understanding of non-stoichiometric ratio, especially for Pu2O3-x, is not deep enough. Based on this, using the DFT + U theoretical scheme of density functional theory, we have systematically studied the structural stability, lattice parameters, electronic structure, mechanical and optical properties of six typical high temperature phases of ß-Pu2O3, α-Pu2O3,γ-Pu2O3, PuO, α-PuO2,γ-PuO2. Further, the mechanical properties and optical behavior of Pu2O3-x under different oxygen vacancy concentrations are analyzed and discussed in detail. The result shows that the elasticity modulus of single crystal in mechanical properties is directly related to the oxygen/plutonium ratio and crystal system. As the number of oxygen vacancies increases, the mechanical constants continue to increase. In terms of optical properties, PuO has the best optical properties, and the light absorption rate decreases with the increase of oxygen vacancy concentration.

Progress and prospect of single-molecular ClpX ATPase researching system-a mini-review.

ClpXP in Escherichia coli is a proteasome degrading protein substrates. It consists of one hexamer of ATPase (ClpX) and two heptamers of peptidase (ClpP). The ClpX binds ATP and translocates the substrate protein into the ClpP chamber by binding and hydrolysis of ATP. At single molecular level, ClpX harnesses cycles of power stroke (dwell and burst) to unfold the substrates, then releases the ADP and Pi. Based on the construction and function of ClpXP, especially the recent progress on how ClpX unfold protein substrates, in this mini-review, a currently proposed single ClpX molecular model system detected by optical tweezers, and its prospective for the elucidation of the mechanism of force generation of ClpX in its power stroke and the subunit interaction with each other, were discussed in detail.

High thermoelectric performances of monolayer SnSe allotropes.

α-SnSe is one of the most promising thermoelectric materials with low thermal conductivity and a high power factor. Since the thermoelectric properties of a material have a strong dependence on its crystal structure, we study the energetic and thermoelectric properties of four new monolayer phases of SnSe (ß, γ, δ and ε) together with α-SnSe using the ab initio density functional theory method. The calculated electronic structures show that all five phases are semiconductors with different band gaps. The α, ß, γ, and δ phases have an indirect band gap with the hybridization of sp2 orbitals, whereas the ε phase has a direct band with the hybridization of sp3 orbitals. The thermoelectric transport properties and coefficients are obtained from the electronic structure using semi-classical Boltzmann theory, and the results indicate that the four new phases of SnSe (ß, γ, δ and ε) all have better thermoelectric properties compared with the reported α phase. The predicted ZT value for the ß-SnSe phase is 2.06 at 300 K, suggesting that it has great potential for novel thermoelectric applications.

Phase diagram and superconductivity of compressed zirconium hydrides.

It is known that pressure can be applied to fundamentally alter the bonding patterns between the chemical elements. By employing an unbiased structure search method based on a particle swarm optimization (PSO) methodology, the phase diagram and crystal structures of Zr-H compounds are systematically investigated at a high pressure up to 150 GPa. Interestingly, some unexpectedly stable compounds with unusual chemical and physical properties are predicted to be formed, for example, four stable and metallic species with stoichiometries of ZrH, ZrH2, ZrH3, and ZrH6 are identified for the first time. It is interesting to note that Cmc21-ZrH6 adopts intriguing structures with H2 units. Surprisingly, it is found that Cmcm-ZrH is superconducting with Tc as high as 10.6 K. Our study opens a novel avenue for designing superconducting Zr-H compounds by applying pressure.

A first-principles study of lithium-decorated hybrid boron nitride and graphene domains for hydrogen storage.

First-principles calculations are performed to investigate the adsorption of hydrogen onto Li-decorated hybrid boron nitride and graphene domains of (BN)(x)C(1-x) complexes with x = 1, 0.25, 0.5, 0.75, 0, and B0.125C0.875. The most stable adsorption sites for the nth hydrogen molecule in the lithium-decorated (BN)(x)C(1-x) complexes are systematically discussed. The most stable adsorption sites were affected by the charge localization, and the hydrogen molecules were favorably located above the C-C bonds beside the Li atom. The results show that the nitrogen atoms in the substrate planes could increase the hybridization between the 2p orbitals of Li and the orbitals of H2. The results revealed that the (BN)(x)C(1-x) complexes not only have good thermal stability but they also exhibit a high hydrogen storage of 8.7% because of their dehydrogenation ability.