Stable structure and electronic properties of Ru1−xTixO2 rutile type solid solutions from DFT calculations

To design solid solution is an effective strategy for functional materials. The complex electron correlation and non-equilibrium atomic interaction are the primary factors to impact the macro-/micro-structure and application performances of solid solution. Hence, this article concentrates on the stable crystal structure and the corresponding electronic structure of Ru_1−xTi_xO₂ solid solution by using density functional theory calculations. Based on analyzing the atomic interaction between solute and solvent atoms, the most stable supercell models for the specific solid solubility were obtained. In Ru_1−xTi_xO₂ solid solution, solute (and solvent) atoms preferentially arrange along the [110] direction, and tend to occupy the nearest sites of identical atoms, to arrange the symmetric ordered substitution configurations. Using the subregular solution model, the mixing enthalpy can be represented by the following expression: . The calculated phase diagram is consistent with the experimental results. Thus, the calculated results in this article are reliable and can provide more meaningful information. In the cases of Ru-rich solid solutions, the metastable phase exists in the range of x < 0.27; while in the cases of Ti-rich solid solutions, the metastable phase exists in the range of x > 0.81. Interestingly, the electron density of Ru_1−xTi_xO₂ solid solutions at Fermi level has a stronger dependence on the Ru composition, which intrinsically influences its electronic structure and optical properties. According to the basic application principle, Ru_1−xTi_xO₂ solid solutions with lower (x < 0.27) and higher (x > 0.81) solid solubility could act as suitable candidate for the applications in field electrochemistry and photocatalysis.     

Chemical dynamics at surfaces

The current status of molecular dynamics simulations of chemical processes at surfaces is assessed. Limitations of the method are discussed, and recent progress towards overcoming the limitations is described. The reliability and depth of understanding achievable through interplay between simulation and experiment is illustrated by a simple example, the trapping of Ar on a Pt(111) crystal surface. The prognosis for extending these techniques to chemically reacting systems in real environments is addressed.     

基于一阶矩的无乘法DFT算法

为快速实现短信号序列的离散傅里叶变换,提出一种基于一阶矩的无乘法DFT算法。通过数学推导将离散傅里叶变换的计算转换为一阶矩的计算,利用1-网络法实现一阶矩的运算。该算法的计算过程仅涉及加法运算,并能独立计算DFT频域系数。实验结果证明了算法的有效性,特别是在某些条件下优于现有的快速傅里叶算法。     

一种基于二维DFT的一对多非对称数字水印算法

针对当今水印系统中的公开验证难题及水印存储信息量大的问题,提出了一种一对多的非对称数字水印算法。该水印算法基于二维离散傅立叶变换(2DFT)。参考水印的相位在2DFT域中被任意地改变,从而得到不同的嵌入水印。这些嵌入水印彼此相关,并且和参考水印均有相同的互相关性。通过比较互相关系数值和判决门限,实现水印检测。仿真结果表明,选择恰当的判决门限,参考水印能正确地检测嵌入水印,而由参考水印生成的其它嵌入水印却不能实现水印检测。参考水印的信息公开不会降低嵌入水印的安全性。因此,该算法实现水印的公开验证,同时只需存储一个参考水印就能检测多个嵌入水印,降低了水印存储信息量。     

Defect formation and its effect on the thermodynamic properties of Pu2Zr2O7 pyrochlore: a first-principles study

In the past decades, pyrochlores, such as Gd₂Zr₂O₇, have demonstrated great potential to immobilize nuclear wastes such as Pu, which results in the production of Pu₂Zr₂O₇. Due to the high radioactivity of Pu, it is difficult to investigate the radiation response behavior of Pu₂Zr₂O₇ and its physical properties of the damaged state experimentally. Consequently, few related data have been reported in the literature thus far. In this study, first-principles calculations have been carried out to investigate the defect formation and its effect on the thermodynamic properties of Pu₂Zr₂O₇. It reveals that Pu_Zr antisite and O_8a interstitial defects are very easy to form in Pu₂Zr₂O₇. In particular, the O_8a interstitial defect can be formed spontaneously, while it is mechanically unstable. When vacancy, interstitial or antisite defects are formed in Pu₂Zr₂O₇, and the elastic moduli and Debye temperature are decreased. Besides, better ductility is resulted. As compared with other zirconate pyrochlores, such as Gd₂Zr₂O₇, the Pu₂Zr₂O₇ is suggested to be less resistant to radiation-induced amorphization. This study demonstrates that the created defects due to self-radiation from actinide decay have remarkable influences on the thermophysical properties of Pu₂Zr₂O₇.     

Computer Simulation of the Process of Quenching Large-Size Parts in Water and Aqueous Solutions

DESPITE of the rapid development of computerfacilities and numerical methods of computing thestress-strain state of large-size parts,the accuracy ofcomputations is not sufficient because of the lack ofaccurate input data.For this reason,heat treatingengineers do not trust computations and are afraid ofquenching of large-size parts in water,in particular,when Bi—>°°.There are some causes of suchsituation:1)Because of inaccurate boundary conditions andincomplete information on mechanical p…     

DFT research on activation of sphalerite

Activation of sphalerite ZnS, (Zn, Fe)S, (Zn, Cu)S were carried out using the density functional theory (DFT) method. The electronic structures and related properties of three kind of zinc sulfide compounds were investigated. In addition, the relation between electronic structure and flotation behavior was discussed. The results show that, ZnS has a broader band gap than (Zn,Cu)S and (Zn,Fe)S do, and it has low electrochemistry activity to react with flotation collectors to render the surface hydrophobic. When the Zn atom in ZnS is replaced by Cu atom,the band gap will be reduced, and the top valence band will be occupied by Cu 3d orbit, thus it is beneficial to the interaction between mineral surface and collector.     

Comparative study of bis-piperidiniummethyl-urea and mono-piperidiniummethyl-urea as volatile corrosion inhibitors for mild steel

Bis-piperidiniummethyl-urea (BPMU) and mono-piperidiniummethyl-urea (MPMU) were developed as novel volatile corrosion inhibitors (VCIs). Their vapor corrosion inhibition property was evaluated by volatile inhibiting sieve test (VIS) and vapor inhibiting ability test (VIA). Volatile weight-loss test in a closed space was used to compare their volatility. Electrochemical impedance spectroscopy of a volatile corrosion inhibitor monitor (VCIM) was applied to study the effect of BPMU and MPMU on the corrosion inhibition of mild steel in thin electrolyte layer. The results show that BPMU has the better protection effect compared with MPMU. Adsorption of BPMU and MPMU on steel surface was investigated by X-ray photoelectron spectroscopy (XPS). It was shown that one BPMU molecule has two N atoms to coordinate with one Fe atom, and that one MPMU molecule has one N atom to coordinate with one Fe atom. The quantum chemical parameters were obtained by PM3 semi-empirical method. BPMU has the smaller HOMO-LUMO energy gap and the smaller net positive charge intensities of 4N and 8N atoms in its molecule.     

L12型Al3Sc基金属间化合物有序化行为和力学性能的第一性原理计算

本文采用亚晶格模型,辅助以第一性原理总能计算,研究了L1₂型Al₃Sc基金属间化合物中元素的占位有序化行为和力学性能。结果表明：Al₃Sc合金呈现完全有序化,其中Al占据3c亚晶格位置,Sc占据1a亚晶格位置；L1₂-Al₃(Sc_0.75M_0.25)金属间化合物(M=Y、Ti、Zr和Hf)也呈现完全有序化,第三组元M均只占据1a亚晶格位置,这些元素的占位行为均不受温度的影响。L1₂-Al₃(Sc_0.75M_0.25)金属间化合物均满足力学稳定性条件。M为Y时,L1₂-Al₃(Sc_0.75M_0.25)金属间化合物的剪切模量、体弹模量和杨氏模量和硬度下降；M为Ti、Zr或Hf时,随着原子半径增大,剪切模量、体弹模量、杨氏模量和硬度逐渐降低,其中Ti的加入可使L1₂-Al₃(Sc_0.75M_0.25)金属间化合物的塑性和韧性达到最好。