First-principles study on the mechanical properties of M2CT2（M=Ti,Zr,Hf;T=O,F,OH） MXenes

Two-dimensional(2D)transition metal carbides known as MXenes belong to a new branch of 2D material family,and their fundamental properties vary with their compositions and surface functionalizations.In this study,the structural and ideal mechanical properties of M2C-type MXenes and their functionalized M2CT2 MXenes(M=Ti,Zr,Hf;T=O,F,OH)were systematically examined via first-principles methods.The stress–strain curves of the MXenes under homogenous biaxial and uniaxial tension are identified,and the fundamental quantities(e.g.,Young’s modulus,in-plane stiffness,and Poisson’s ratio)are addressed.With significantly higher strength and extended critical strains,the M2CO2 MXenes exhibit optimal flexibility when compared with that of M2C,M2CF2,and M2C(OH)2.Additionally,Hf2CT2 exhibits optimal tensile performance under uniaxial or biaxial tension when compared to that of Ti2CT2 and Zr2CT2.The Young’s modulus,in-plane stiffness,and Poisson’s ratio of MXenes with different surface functionalization increase in a sequence corresponding to OH\F\O.Furthermore,the effects of vacancy on the mechanical properties of MXenes are further explored and indicate that vacancy can significantly weaken the tensile properties of MXenes that are considered.Moreover,vacancy also results in a certain anisotropy of stress along armchair and zigzag directions even under the biaxial tension condition.

First-principles study on nonlocal ferromagnetism in (Cu, N)-codoped ZnO

First-principles calculations based on spin density functional theory are performed to study the spin-resolved elec- tronic properties of ZnO codoped with Cu and N. （Cu, N）-codoped ZnO exhibits magnetism, and the total magnetic mo- ment mainly originates from the p--d hybridization of Cu-N and Cu-O as well as p--p coupling interaction between N and O at the Fermi level. The Zn34Cu2035N1 favors energetically a ferromagnetic ground state due to the existence of stable Cu-N-Cu complex. These results imply that the （Cu, N）-codoped ZnO is a promising dilute magnetic semiconductor free of magnetic precipitates, which could broaden the horizon of currently known magnetic systems.

Relaxations and bonding mechanism of arsenic in-situ impurities in MCT: first-principles study

The structural and electronic properties of the arsenic in-situ impurity in Hg1?xCdxTe(MCT) were studied by combining the full-potential linear augmented plane wave (FP-LAPW) and plane-wave pseudopotential methods base on the density functional theory. Structural relaxations, local charge density, densities of states are computed to investigate the effects of the impurity on the electronic structure. The bonding characteristics between the impurity and the host atoms are discussed by analysis of the valence charge density and the bonding charge density. The amphoteric behavior of arsenic impurity in MCT has been shown. The defect levels introduced by the in-situ arsenic impurities are determined by the single-particle electron energy calculations, which are in good agreement with the experimental results.

First-principles study of helium clustering at initial stage in ThO2

The clustering behavior of helium atoms in thorium dioxide has been investigated by first-principles calculations. The results show that He atoms tend to form a cluster around an octahedral interstitial site（OIS）. As the concentration of He atoms in ThO2 increases, the strain induced by the He atoms increases and the octahedral interstitial site is not large enough to accommodate a large cluster, such as a He hexamer. We considered three different Schottky defect（SD） configurations（SD1, SD2, and SD3）. When He atoms are located in the SD sites, the strain induced by the He atoms is released and the incorporation and binding energies decrease. The He trimer is the most stable cluster in SD1. Large He clusters, such as a He hexamer, are also stable in the SDs.

First-principles Investigation of the Structural, Electronic and Elastic Properties of Al_2Ca and Al_4Sr Phases in Mg-Al-Ca(Sr) Alloy

First-principles calculations have been carried out to investigate the structural stabilities, electronic structures and elastic properties of Mg17Al12, Al2Ca and Al4Sr phases. The optimized structural parameters are in good agreement with the experimental and other theoretical values. The calculated formation enthalpies and cohesive energies show that Al2Ca has the strongest alloying ability, and Al4Sr has the highest structural stability. The densities of states （DOS）, Mulliken electronic populations, and electronic charge density difference are obtained to reveal the underlying mechanism of structural stability. The bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio are estimated from the calculated elastic constants. The mechanical properties of these phases are further analyzed and discussed. The Gibbs free energy and Debye temperature are also calculated and discussed.

The First Principles Study of Hydrogen Adsorption on Ni-Decorated LiB(001) Surface

The hydrogen adsorption on the one and three Ni-decorated LiB （001） 2 × 2 surface is investigated by the first principles study. It is demonstrated that Ni atoms are preferentially adsorbed on the top B atom, and form a covalent bond of NiB and an ionic bond of NiLi on the surface. Four H2 molecules can adsorb on the one- Ni-decorated LiB （001） surface, and the average adsorption energy is in a range from -0.35 to -0.58eV/H2. The charge population analysis shows that the dipole moments on the Ni decorated surface is responsible for the polarization and adsorption of H2. Then, we show that three Ni atoms can be decorated on the LiB （001） 2 × 2 surface, and form a Ni3B nano cluster on the surface, which agrees with experimental results. Three Ni- decorated LiB （001） can adsorb up to six H2 molecules, indicating that the Ni-decorated LiB （001） system might be a promising hydrogen storage material.

Applying“First Principles of Instruction”as a Design Theory of the EFL Classroom:Findings from an Empirical Study

How to benefit the learners learning English as a foreign language(EFL)from the aspect of instructional design aroused the concerns of many teachers and researchers.The main purpose of this study is to address the question of how teachers can design and implement EFL classroom that benefit the learners.Specifically,the“First Principles of Instruction,”advocated by Merrill(2002),was applied by the English teachers to conduct their day-to-day pedagogical practices.The corresponding effects of this theory in designing EFL classroom activities were reported in this study.Two research questions are formulated as follows:(1)Does the“First Principles of Instruction”benefit the EFL classroom designing in the aspect of student achievement?If yes,what is the effect?(2)How do the English teachers perceive the“First Principles of Instruction”to design EFL classroom?While observing the EFL classroom activities and interviewing the college English teachers,an empirical study was done to perceive how college English teachers could best apply these principles to design EFL classroom activities.

Coadsorption of gold with chlorine on CeO_2(111) surfaces:A first principles study

To investigate the effects of chlorine on the Au/ceria catalysts,the adsorption of gold or chlorine and their coadsorpiton on the stoichiometric and partially reduced CeO2（111） surfaces are studied from the first principles.It is found that the adsorption of Au is significantly enhanced by the chlorine preadsorption on the stoichiometric CeO2（111） surface;while on the partially reduced CeO2（111） surface,the preadsorbed chlorine inhabits the oxygen vacancy（which is the preferred adsorption site for gold）,leading to a CeOCl phase and the dramatical weakening of the Au adsorption.Therefore,chlorine on the CeO2（111） surface can affect the Au adsorption thus the activity of the Au/CeO2 catalyst.

First Principles Study on Mechanical Properties of Superhard α-Ga Boron

The mechanical properties and intrinsic hardness of the α-Ga boron phase （α-Ga-B） are studied by using the combination of first-principles calculations and a semiempirieal macroscopic hardness model. It is found that α- Ga-B is mechanically stable and possesses higher bulk/shear modulus as compared with γ-B28, a newly discovered high-pressure boron phase. The theoretical hardness of α-Ga-B is estimated to be 45 GPa, which is much higher than 38 GPa for γ-B28. The results strongly indicate that α-Ga-B is a potential superhard boron phase. To further obtain insight into the superhard nature of α-Ga-B, we simulate stress-strain curves under tensile and shear deformation. Meanwhile, the microscopic mechanism driving the tensile and shear deformation modes in α-Ga-B is discussed in detail.

First-principle study on optical properties of N-La-codoped anatase TiO

The electronic structures, deformation charge density, dipole moment, and optical properties of N-La-codoped anatase titanium dioxide （TiO2） are studied using the plane-wave ultrasoft pseudopotential method based on the density functional theory （DFT）. The optical properties of two-ion-doped TiO2 are analyzed via electronic structures, deformation charge density, and dipole moment. For the model of N-La-doped TiO2, a smaller atom fraction of N and La atoms induces better optical properties. The absorption edges of two doped TiO2 models redshift to the visible-light region.

Linear optical properties of defective KDP with oxygen vacancy: First-principles calculations

The linear optical properties of potassium dihydrogen phosphate（KDP） with oxygen vacancy are investigated with first-principles density functional theory calculations. We use Heyd–Scuseria–Ernzerhof（HSE06） functional to calculate the linear optical properties because of its accuracy in the band gap calculation. Compared with the perfect KDP, we found that due to the defect states located at the band gap, the defective KDP with oxygen vacancy has new optical adsorption within the energy region from 4.8 eV to 7.0 eV（the corresponding wavelength region is from 258 nm to 177 nm）. As a result, the oxygen vacancy can decrease the damage threshold of KDP crystal. It may give a direction to the KDP production for laser system.

First Principle Study on Optical Properties of Tri-Group Doped(6,6) SiC Nanotubes

The optical properties of tri-group（B, Al, Ga, In） doped（6,6） SiC nanotubes（SiCNTs） are studied from first principles. The results show that the main absorption and dispersion of SiCNTs caused by the intrinsic transition appear in the ultraviolet-visible region（below 500 nm）, and the tri-group doping increases the minimum dielectric constant value resulting in enhanced transmittance. In addition, the tri-group doping can introduce a weak absorption and dispersion region in the near-mid-infrared region, and the response peak blue shifts as the diameter of the doping atom increases. Comparative studies of reflectance, absorptivity, and transmittance show that the key factors affecting the transmittance of SiCNTs are reflectance（or refractive index） rather than absorption coefficient.

First principles investigation of protactinium-based oxide-perovskites for flexible opto electronic devices

The structural,elastic,mechanical,electronic,and optical properties of KPaO_3 and RbPaO_3 compounds are investigated from first-principles calculations by using the WIEN2 k code in the frame of local density approximation（LDA） and generalized gradient approximation（GGA）.The calculated ground state quantities,such as lattice constant（α_0）,ground state energy（E）,bulk modulus（S）,and their pressure derivative（B_p） are in reasonable agreement with the present analytical and previous theoretical results and available experimental data.Based on several elastic and mechanical parameters,the structural stability,hardness,stiffness and the brittle and ductile behaviors are discussed,which reveal that protactiniumbased oxide series of perovskites is mechanically stable and possesses weak resistance to shear deformation compared with resistance to unidirectional compression while flexible and covalent behaviors are dominated in them.The analysis of band profile through Trans-Blaha modified Becke-Johnson（TB-mBJ） potential highlights the underestimation of bandgap with traditional density functional theory（DFT） approximation.Specific contribution of electronic states is investigated by means of total and partial density of states and it can be evaluated that both compounds are（Γ-Γ） direct bandgap semiconductors.All fundamental optical properties are analyzed while attention is paid to absorption and reflection spectra to explore extensive absorptions and reflections of these compounds in high frequency regions.The present method represents an influential approach to calculating the whole set of elastic,mechanical,and opto-electronic parameters,which would conduce to the understanding of various physical phenomena and empower the device engineers to implement these materials in flexible opto-electronic applications.

Study on Active Principle and Modernization of Chinese Drugs

The people as a whole cannot live for one day without drug, and the requirement of drugs would never come to an end or stay on the same level. Pharmaceutical industry, being of great significance, has become a new and important one in economic growth in the 21st century. Therefore, the modernization of Chinese drugs has also become a hot spot in public opinion in recent years.

A Calorimetric Study Assisted with First Principle Calculations of Specific Heat for Si-Ge Alloys within a Broad Temperature Range

Calorimetric measurements are performed to determine the specific heat of Si-xat.% Ge(where x = 0, 10, 30,50, 70, 90 and 100) alloys within a broad temperature range from 123 to 823 K. The measured specific heat increases dramatically at low temperatures, and the composition dependence of specific heat is evaluated from the experimental results. Meanwhile, the specific heat at constant volume, the thermal expansion, and the bulk modulus of Si and Ge are investigated by the first principle calculations combined with the quasiharmonic approximation. The negative thermal expansion is observed for both Si and Ge. Furthermore, the isobaric specific heat of Si and Ge is calculated correspondingly from OK to their melting points, which is verified by the measured results and accounts for the temperature dependence in a still boarder range.

First principle study on the possibilities of magnetism in one-dimensional In and Tl atomic wires with the full-potential linearized augmented plane wave method

Using ab initio total energy calculations with the full-potential linearized augmented plane wave method, the possibilities of magnetism in one-dimensional In and Tl wires were explored and their properties as the function of geometric structures were studied. The results suggest that the linear In and Tl wires show magnetization at the equilibrium bond distance with magnetic moments of 0.71 and 0.67 μB/atom, respectively. Allowing ions to relax, the wires were deformed as zigzag structures, but no dimerization occurs. The zigzag wires also exhibit spontaneous magnetization, although the magnetic moments are lower than those of straight wires.

Translation Studies的名与实——再议“Translation Studies”一词的汉译

“Translation Stud ies”一词的汉译,我国学界有不同的主张。其实,该词具有“翻译学”和“翻译研究”的双重译名,我们应以“名实相符”为原则,根据其不同所指赋予其不同的汉译名予以区分。同时,依据这一原则对我国引进的部分国外学术专著的书名的汉译应进行修改。

Mechanism study on flotation separation of molybdenite from chalcocite using thioglycollic acid as depressant

Effects of collectors(butyl xanthate(BX), O-isopropyl-N-sulfur ethyl carbamate(Z-200) and emulsified kerosene), dereagent(sodium sulfide) and depressant thioglycollic acid(TGA) on the flotation of chalcocite and molybdenite were investigated through flotation. The first principle theory was adopted to understand the difference of their surfaces and reaction between minerals and reagents. Results of flotation tests revealed that selectivity of emulsified kerosene is the best of three collectors in separation of chalcocite and molybdenite, though the others also display excellent collecting properties. Sodium sulfide can effectively remove collectors adsorbed on chalcocite surface, and TGA is an effective depressant of chalcocite at pH 8-9. Through first principle study, molybdenite displays relatively stronger covalence property while bonding interaction between copper atoms in chalcocite enhanced its ionicity. Bonding interaction is weaker in reaction of TGA and molybdenite, so it shows higher hydrophobicity and better flotability. Therefore, TGA is an effective inhibitor in the separation.