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elastic properties of CaCO3 high pressure phases from first principles

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Chinese Physics B 2017年第8期26卷 587-594页

作者：黄丹刘红侯明强谢梦雨鹿亚飞刘雷易丽崔月菊李营邓力维杜建国 CEA Key Laboratory of Earthquake Prediction(Institute of Earthquake Science) China Earthquake Administration(CEA)Beijing 100036China National Key Laboratory of Shock Wave and Detonation Physics Institute of Fluid PhysicsChina Academy of Engineering PhysicsMianyang 621900China Center for High Pressure Science and Technology Advanced Research Shanghai 201203China Institute of Geology and Geophysics Chinese Academy of SciencesBeijing 100029China

elastic properties of three high pressure polymorphs of CaCO_3 are investigated based on first principles *** calculations are conducted at 0 GPa–40 GPa for aragonite, 40 GPa–65 GPa for post-aragonite, and 65 GPa–150 GPa for the P2_1/c-h-CaCO_3 structure, respectively. By fitting the third-order Birch–Murnaghan equation of state（EOS）, the values of bulk modulus K_0 and pressure derivative K~＇_0 are 66.09 GPa and 4.64 for aragonite, 81.93 GPa and 4.49 for post-aragonite, and 56.55 GPa and 5.40 for P2_1/c-h-CaCO_3, respectively, which are in good agreement with previous experimental and theoretical data. elastic constants, wave velocities, and wave velocity anisotropies of the three highpressure CaCO_3 phases are obtained. Post-aragonite exhibits 25.90%–32.10% V_P anisotropy and 74.34%–104.30% V_S splitting anisotropy, and P2_1/c-h-CaCO_3 shows 22.30%–25.40% V_Panisotropy and 42.81%–48.00% V_S splitting anisotropy in the calculated pressure range. Compared with major minerals of the lower mantle, CaCO_3 high pressure polymorphs have low isotropic wave velocity and high wave velocity anisotropies. These results are important for understanding the deep carbon cycle and seismic wave velocity structure in the lower mantle.

关键词： CaCO3 elastic properties wave velocity anisotropy first principles

elastic properties of Nb-based alloys by using the density functional theory

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Chinese Physics B 2012年第1期21卷 357-362页

作者：刘增辉尚家香 School of Materials Science and Engineering Beihang University

A first-principles density functional approach is used to study the electronic and the elastic properties of Nb15X （X = Ti, Zr, Hf, V, Ta, Cr, Mo, and W） alloys. The elastic constants cn and c12, the shear modulus CI, and the elastic modulus E（lOO） are found to exhibit similar tendencies, each as a function of valence electron number per atom （EPA）, while c44 seems unclear. Both cu and c12 of Nb15X alloys increase monotonically with the increase of EPA. The C/ and E000） also show similar tendencies. The elastic constants （except c44） increase slightly when alloying with neighbours of a higher d-transition series. Our results are supported by the bonding density distribution. When solute atoms change from Ti（Zr, Hf） to V（Ta） then to Cr（Mo, W）, the bonding electron density between the central solute atom and its first neighbouring Nb atoms is increased and becomes more anisotropic, which indicates the strong interaction and thus enhances the elastic properties of Nb-Cr（Mo, W） alloys. Under uniaxial {100） tensile loading, alloyed elements with less （more） valence electrons decrease （increase） the ideal tensile strength.

关键词： Nb-based alloys elastic properties density functional calculations

elastic properties and electronic structures of lanthanide hexaborides

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Chinese Physics B 2015年第9期24卷 367-375页

作者：段婕周彤张莉杜际广蒋刚王宏斌 Institute of Atomic and Molecular Physics Sichuan University College of Physical Science and Technology Sichuan University

The structural, elastic, and electronic properties of a series of lanthanide hexaborides（Ln B6） have been investigated by performing ab initio calculations based on the density functional theory using the Vienna ab initio simulation *** calculated lattice and elastic constants of Ln B6 are in good agreement with the available experimental data and other theoretical results. The polycrystalline Young＇s modulus, shear modulus, the ratio of bulk to shear modulus B/G, Poisson＇s ratios, Zener anisotropy factors, as well as the Debye temperature are calculated, and all of the properties display some regularity with increasing atomic number of lanthanide atoms, whereas anomalies are observed for Eu B6 and Yb B6. In addition, detailed electronic structure calculations are carried out to shed light on the peculiar elastic properties of Ln *** total density of states demonstrates the existence of a pseudogap and indicates lower structure stability of Eu B6 and Yb B6 compared with others.

关键词： elastic properties electronic structure ab initio calculations thermodynamic properties

A method of determining effective elastic properties of honeycomb cores based on equal strain energy

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Chinese Journal of Aeronautics 2017年第2期30卷 766-779页

作者： Qiu Cheng Guan Zhidong Jiang Siyuan Li Zengshan School of Aeronautic Science and Engineering Beihang University Bejing 100083 China

A computational homogenization technique（CHT） based on the finite element method（FEM） is discussed to predict the effective elastic properties of honeycomb *** need of periodic boundary conditions（BCs） is revealed through the analysis for in-plane and out-of-plane shear moduli of models with different cell *** applying periodic BCs on the representative volume element（RVE）,comparison between the volume-average stress method and the boundary stress method is performed,and a new method based on the equality of strain energy to obtain all non-zero components of the stiffness tensor is *** of finite element（FE） analysis show that the volume-average stress and the boundary stress keep a consistency over different cell geometries and *** strain energy method obtains values that differ from those of the volume-average method for non-diagonal terms in the stiffness *** has been done on numerical results for thin-wall honeycombs and different geometries of angles between oblique and vertical *** inaccuracy of the volume-average method in terms of the strain energy is shown by numerical benchmarks.

关键词： elastic properties Homogenization Honeycomb Strain energy Unit cells

Characterisation of the high-pressure structural transition and elastic properties in boron arsenic

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Chinese Physics B 2010年第7期19卷 430-436页

作者：吕兵令狐荣锋易勇杨向东 Institute of Atomic and Molecular Physics Sichuan University School of Physics and Electronic Science Guizhou Normal University School of Materials Science and Engineering Southwest University of Science and Technology

This paper carries out the First principles calculation of the crystal structures （zinc blende （B3） and rocksalt （B1）） and phase transition of boron arsenic （BAs） based on the density-functional theory. Using the relation between enthalpy and pressure, it finds that the transition phase from the B3 structural to the B] structural occurs at the pressure of l13.42GPa. Then the elastic constants Cll, C12, C44, bulk modulus, shear modulus, Young modulus, anisotropy factor, Kleinman parameter and Poisson ratio are discussed in detail for two polymorphs of BAs. The results of the structural parameters and elastic properties in B3 structure are in good agreement with the available theoretical and experimental values.

关键词： phase transition elastic properties generalised gradient approximation boron arsenic

Thermodynamics and elastic properties of Ta from first-principles calculations

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Chinese Physics B 2012年第12期21卷 412-419页

作者：李强黄多辉曹启龙王藩侯蔡灵仓张修路经福谦 Computational Physics Key Laboratory of Sichuan Province Yibin University Key Laboratory of National Defense Science and Technology for Shock Wave and Detonation Physics and the Science

Within the framework of the quasiharmonic approximation, the thermodynamics and elastic properties of Ta, including phonon density of states （DOS）, equation of state, linear thermal expansion coefficient, entropy, enthalpy, heat capacity, elastic constants, bulk modulus, shear modulus, Young＇s modulus, microhardness, and sound velocity, are studied using the first-principles projector-augmented wave method. The vibrational contribution to Helmholtz free energy is evaluated from the first-principles phonon DOS and the Debye model. The thermal electronic contribution to Helmholtz free energy is estimated from the integration over the electronic DOS. By comparing the experimental results with the calculation results from the first-principles and the Debye model, it is found that the thermodynamic properties of Ta are depicted well by the first-principles. The elastic properties of Ta from the first-principles are consistent with the available experimental data.

关键词： first-principles Ta thermodynamics Debye model elastic properties

Temperature Dependent Thermal and elastic properties of High Entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2):Molecular Dynamics Simulation by Deep Learning Potential

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Journal of Materials Science & Technology 2021年第13期72卷 8-15页

作者： Fu-Zhi Dai Yinjie Sun Bo Wen Huimin Xiang Yanchun Zhou Science and Technology on Advanced Functional Composite Laboratory Aerospace Research Institute of Materials&Processing TechnologyBeijing100076China

High entropy diborides are new categories of ultra-high temperature ceramics,which are believed promising candidates for applications in hypersonic ***,knowledge on high temperature thermal and mechanical properties of high entropy diborides is still lacking unit *** this work,variations of thermal and elastic properties of high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) with respect to temperature were predicted by molecular dynamics ***,a deep learning potential for Ti-Zr-Hf-Nb-Ta-B diboride system was fitted with its prediction error in energy and force respectively being 9.2 meV/atom and 208 meV/A,in comparison with first-principles ***,temperature dependent lattice constants,anisotropic thermal expansions,anisotropic phonon thermal conductivities,and elastic properties of high entropy(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) from 0℃to 2400℃were evaluated,where the predicted room temperature values agree well with experimental *** addition,intrinsic lattice distortions of(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) were analyzed by displacements of atoms from their ideal positions,which are in an order of 10^(-3) A and one order of magnitude smaller than those in(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))*** indicates that lattice distortions in(Ti_(0.2)Zr_(0.2)Hf_(0.2)Nb_(0.2)Ta_(0.2))B_(2) is not so severe as *** the new paradigm of machine learning potential,deep insight into high entropy materials can be achieved in the future,since the chemical and structural complexly in high entropy materials can be well handled by machine learning potential.

关键词： High entropy diborides Machine learning potential Thermal properties elastic properties Molecular dynamics

Effect of pressure on the elastic properties and optoelectronic behavior of Zn_4B_6O_(13): First-principles investigation

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Chinese Physics B 2018年第5期27卷 430-439页

作者： Pei-Da Wang Zhen-Yuan Jia Yu-Han Zhong Hua-Yue Mei Chun-Mei Li Nan-Pu Cheng Faculty of Materials and Energy Southwest University Chongqing 400715 China

The hydrostatic-pressure-dependent mechanical stability and optoelectronic behavior of Zn_4B_6O_（13）（ZBO） are calculated using the exchange-correlation functional Perdew–Burke–Ernzerhof generalized gradient approximation and the hybrid functional PBE0 based on density functional theory. The calculated and experimental unit cell volumes and Vickers hardness of ZBO at zero pressure agree well. ZBO is mechanically stable under the critical pressure of 52.98 GPa according to the generalized stability criteria. Furthermore, Young＇s modulus and Vickers hardness decrease with increasing hydrostatic pressure. The strength and type of ZBO bonds are investigated by population and electron density difference. The electronic structure at zero pressure reveals that ZBO is an indirect band gap semiconductor, and the calculated 5.62-e V bandgap coincides well with the 5.73-e V experimental value, highlighting the success of the hybrid functional PBE0 calculations of electronic properties. The band gap almost increases as a second-order polynomial of pressure, and the indirect nature does not change with the applied external pressure. The optical reflectivity and absorption coefficient show that ZBO is an excellent ultraviolet photodetector. Our calculation results suggest that the elastic and optical properties of ZBO are highly stable over a wide pressure range.

关键词： Zn4B6O13 crystal density functional theory elastic properties optical properties

Electronic structures and elastic properties of monolayer and bilayer transition metal dichalcogenides MX_2(M= Mo,W;X= O,S,Se,Te):A comparative first-principles study

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Chinese Physics B 2015年第9期24卷 436-443页

作者：曾范张卫兵唐壁玉 Department of Physics Xiangtan University School of Physics and Electronic Sciences Changsha University of Science and Technology School of Chemistry and Chemical Engineering Guangxi University

First-principle calculations with different exchange-correlation functionals, including LDA, PBE, and vd W-DF functional in the form of opt B88-vd W, have been performed to investigate the electronic and elastic properties of twodimensional transition metal dichalcogenides（TMDCs） with the formula of MX2（M = Mo, W; X = O, S, Se, Te） in both monolayer and bilayer structures. The calculated band structures show a direct band gap for monolayer TMDCs at the K point except for MoO2 and WO2. When the monolayers are stacked into a bilayer, the reduced indirect band gaps are found except for bilayer WTe2, in which the direct gap is still present at the K point. The calculated in-plane Young moduli are comparable to that of graphene, which promises possible application of TMDCs in future flexible and stretchable electronic devices. We also evaluated the performance of different functionals including LDA, PBE, and opt B88-vd W in describing elastic moduli of TMDCs and found that LDA seems to be the most qualified method. Moreover, our calculations suggest that the Young moduli for bilayers are insensitive to stacking orders and the mechanical coupling between monolayers seems to be negligible.

关键词： transition metal dichalcogenides bilayer structures elastic properties electronic structure