Calculation Of Elastic Properties Research Articles

First-principle calculations of elastic, electronic and thermodynamic properties of TiC under high pressure

First-principle investigations of the elastic, electronic and thermodynamic properties of TiC in NaCl structure under high pressure are conducted by using the plane-wave pseudopotential method and quasi-harmonic Debye model. The obtained lattice parameters, elastic constants and moduli at p=0 GPa and T=0 K are in very good agreement with the available experimental data and other theoretical results. According to the analysis of the density of states, the Ti-C bond becomes stronger with pressure increasing. The values of bulk modulus, thermal expansion coefficient, Debye temperature, entropy, Grüneisen parameter and heat capacity (CV) at different pressures and temperatures are obtained successfully by using the quasi-harmonic Debye model. The influence of pressure on bulk modulus, thermal expansion parameter and Debye temperature is greater than that of temperature. The CV decreases with the increase of pressure under the same temperature and tends to the Dulong-Petit limit at high temperature.

Ab initio calculation of phase transitions, elastic, and thermodynamic properties of MnPd alloys

The phase transitions, elastic and thermodynamic properties of MnPd are investigated using first-principles calculations. The elastic constant calculations indicate that the paramagnetic cubic structure is unstable to external strain and the softening of C11-C12 triggers the paramagnetic cubic phase transformation. The paramagnetic tetragonal structure is mechanically and dynamically stable. When considering the magnetic property, a antiferromagnetic tetragonal structure is lower in energy than the paramagnetic tetragonal structure. So we can conclude that the structural behaviors of MnPd alloys change from paramagnetic cubic to paramagnetic tetragonal, and then to antiferromagnetic tetragonal structure. Moreover, we employ quasiharmonic approximation to calculate the heat capacity and the Debye temperature.

Metric between buckling structures and elastic properties in physisorbed polymer-tethered lipid monolayers

The current study reports the use of buckling structures as a measure of film elasticity on physisorbed, solid-supported polymer-tethered lipid monolayers consisting of phospholipids and poly(ethylene glycol) (PEG) lipopolymers. These monolayer systems, built using the Langmuir–Blodgett (LB) technique, exhibit buckles over a wide range of lipopolymer concentrations. Systematic quantitative analysis of the buckling structures using epifluorescence microscopy and atomic force microscopy reveals that increased lipopolymer concentrations are associated with higher area fractions of buckling regions. Quantitative analyses of buckling profiles show, furthermore, that enhanced lipopolymer concentrations lead to increased buckling widths without notably altering buckling amplitude. On the basis of these experimentally determined buckling parameters, we are able to derive a metric between elastic properties and buckling structures in the polymer-tethered lipid monolayer system. This is achieved by combining mean-field calculations of elastic properties of polymer-tethered lipid membranes with buckling theory of an Euler column. Our findings are significant because they provide new insight into the fascinating materials properties of polymer-lipid supramolecular assemblies and represent a tool for the characterization of elastic properties in complex biomembrane-mimicking film architectures with buckling structures.

Pressure-induced structural phase transition in RbAu

Using the first principle method based on density functional theory, the structural and elastic properties calculations of RbAu have been performed. The results demonstrate that RbAu is stable in the CsCl structure ( B2) at ambient pressure, which is in well agreement with the experimental results. And there exists a structural phase transition from CsCl-type structure ( B2) to NaTi-type structure ( B32) at the transition pressure of approximate 6 GPa. The pressure effects on the elastic properties are discussed and the elastic property calculation indicates elastic instability maybe provide phase transition driving force according to the variations relation of the elastic constant versus pressure.

First-principles calculations of structural, electronic, and elastic properties of MgZrSi 2O 7

For the first time, the recently synthesized pyrochlore MgZrSi 2O 7 [J. Xu et al., Mater. Chem. Phys. 128 (2011) 410] has been analyzed using the first principles calculations. The electronic and elastic properties were predicted; in particular, the band gap is indirect and has the value of 6.75 eV. The bulk modulus equals to 186.51 ± 1.95 GPa. Anisotropy of elastic properties was analyzed by comparing the upper and lower estimates of the shear moduli. In addition, directional dependence of the Young's modulus was calculated and visualized; its value varies in the range from 249.7 GPa (along the a, b, c crystallographic axes) to 136.84 GPa (along the bisector direction in any of the ab, bc, ac planes).

Structural, elastic, vibrational and electronic properties of amorphous Al2O3 from ab initio calculations

First-principles molecular dynamics calculations of the structural, elastic, vibrational and electronic properties of amorphous Al2O3, in a system consisting of a supercell of 80 atoms, are reported. A detailed analysis of the interatomic correlations allows us to conclude that the short-range order is mainly composed of AlO4 tetrahedra, but, in contrast with previous results, also an important number of AlO6 octahedra and AlO5 units are present. The vibrational density of states presents two frequency bands, related to bond-bending and bond-stretching modes. It also shows other recognizable features present in similar amorphous oxides. We also present the calculation of elastic properties (bulk modulus and shear modulus). The calculated electronic structure of the material, including total and partial electronic density of states, charge distribution, electron localization function and the ionicity for each species, gives evidence of correlation between the ionicity and the coordination for each Al atom.

First-principles calculations of electronic, optical and elastic properties of Ba 2MgWO 6 double perovskite

The structural, electronic, optical and elastic properties of the cubic double perovskite Ba 2MgWO 6 were calculated using the ab initio plane wave method and compared with the available experimental data. The pressure effects were modeled by optimizing the crystal lattice structure and calculating the band gap at elevated hydrostatic pressures. The calculated values of the relative change of a unit cell volume with pressure are in excellent agreement with the recent experimental measurements [S. Meenakshi et al, J. Phys. Chem. Solids 72 (2011) 609]. The pressure coefficients of the lattice constant and the WO, MgO, BaO bonds variations were all evaluated. Elastic anisotropic properties were analyzed by calculating all independent components of the elastic constants tensor; the greatest and the smallest values of the Young's moduli were determined.

First-Principles Calculations of Structural, Elastic and Electronic Properties of Tetragonal HfO2 under Pressure

Structural, elastic and electronic properties of tetragonal HfO2 at applied hydrostatic pressure up to 50 GPa have been investigated using the plane-wave ultrasoft pseudopotential technique based on the first-principles density-functional theory (DFT). The calculated ground-state properties are in good agreement with previous theoretical and experimental data. Six independent elastic constants of tetragonal HfO2 have been calculated at zero pressure and high pressure. From the obtained elastic constants, the bulk, shear and Young's modulus, Poisson's coefficients, acoustic velocity and Debye temperature have been calculated at the applied pressure. Band structure shows that tetragonal HfO2 is an indirect band gap. The variation of the gap versus pressure is well fitted to a quadratic function.

Ab initio lattice dynamics of Ni 2MnX (X = Sn, Sb) magnetic shape memory alloys

In this study, we present the results of first principles calculations of elastic constants and phonon properties of nickel–manganese based magnetic shape memory compounds Ni 2MnSn and Ni 2MnSb in stoichiometric composition. The plane wave basis sets and pseudopotential method within spin-polarized generalized gradient approximation ( σ-GGA) scheme of the density functional theory is applied. In investigation of the phonon dispersion spectra, linear response technique of the Density Functional Perturbation Theory is used. Phonon softening is observed in dispersion spectra at the transverse acoustic mode (TA 2) in [ ζ ζ 0] direction as an indication of the structural instability of these systems to shear deformation. The vibrational instability of Ni 2MnSb system is larger than that of Ni 2MnSn yielding negative phonon frequencies. This vibrational anomaly is also verified by the low shear modulus and large elastic anisotropy ratio. The minority spin Fermi surfaces of both systems exhibit strong nesting features.

Ab Initio Calculations of Structural, Electronic, Optical and Elastic Properties of CsXBr3 (X =Ca, Ge, Sn)

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First-Principles Calculations of Elastic and Thermodynamic Properties of Cubic CdTe

the equilibrium lattice constants, elastic and thermodynamic properties of cubic CdTe are systemically investigated at high temperature using the plane-wave pseudopotential method as well as the quasi-harmonic Debye model. The bulk modulus of CdTe are calculated as a function of temperature up to 1000K, the relationship between bulk modulusBand pressure is also obtained. The results gained from this model will provide overall predictions accurately for the temperature and pressure dependence of various quantities such as the bulk modulus, the heat capacity and the thermal expansion coefficient. More over, the dependences between Debye temperature and temperature are also successfully obtained. Our results are compared with the experimental data and discussed in light of previous works.

Quasiharmonic thermal elasticity of crystals: An analytical approach

First-principles quasiharmonic calculations play a very important role in mineral physics because they can predict the structural and thermodynamic properties of materials at pressure and temperature conditions of the Earth’s interior that are still challenging for experiments. They also enable calculations of thermal elastic properties by providing second-order derivatives of free energies with respect to strain. The latter are essential to interpret seismic tomography of the mantle in terms of temperature, composition, and mineralogy, in the context of geophysical processes. However, these are exceedingly demanding computations requiring up to ∼10 3 parallel jobs running on tens or more processors each. Here we introduce an analytical and computationally simpler approach that requires only calculations of static elastic constants and phonon density of states for unstrained configurations. This approach, currently implemented for crystals with up to orthorhombic symmetry, decreases the computational effort, i.e., CPU time and human labor, by up to two orders of magnitude. Results for the major mantle phases periclase (MgO) and forsterite (α-Mg2SiO4) show excellent agreement with previous first-principles results and experimental data.

In-plane effective elastic properties of a novel cellular core for sandwich structures

Within this paper an analytical model is presented for the calculation of the in-plane effective elastic properties E x and E y of a novel cellular structure which is proposed to be used as a core in sandwich structures. The proposed cellular core may represent a less expensive and easily to produce alternative to the already known cellular structures used for the construction of sandwich structures. The developed analytical model is validated through experimental tests. The results obtained by analyzing the theoretical model show a good agreement with the tests. The structure topology is studied using a parameterized unit cell and it is shown the way in which the in-plane stiffness depends on the geometric parameters and relative density of the core.

First-principles calculations of structural, electronic, optical, elastic properties and microscopic crystal field effects in Rb 2CrF 6

In the present work we report on the results of ab initio calculations of the optimized crystal structure, band structure, density of states (DOS), optical and elastic properties of Rb 2CrF 6, followed by the microscopic analysis of the crystal field effects for the 3d states of Cr 4+ ions. For the sake of consistency, both the local density approximation (LDA) and generalized gradient approximation (GGA) implemented in the CASTEP module of Materials Studio were used. The pressure dependences of the structural, electronic and elastic properties were analyzed for elevated pressures from 0 to 5 GPa with a step of 1 GPa. In addition, the dependence of the Cr 4+ 3d states’ positions on pressure has been analyzed carefully. The analytical dependences of the crystal field strength 10 Dq on both pressure and Cr–F distance were obtained. To the best of the authors’ knowledge, there are no experimental data on the band structure, elastic constants and absorption spectrum function for this host, so the present work is the first theoretical study of this kind, and the theoretically obtained results could be suggestions for future experiments.

Combining self-consistent and numerical methods for the calculation of elastic fields and effective properties of 3D-matrix composites with periodic and random microstructures

The work is devoted to the calculation of static elastic fields in 3D-composite materials consisting of a homogeneous host medium (matrix) and an array of isolated heterogeneous inclusions. A self-consistent effective field method allows reducing this problem to the problem for a typical cell of the composite that contains a finite number of the inclusions. The volume integral equations for strain and stress fields in a heterogeneous medium are used. Discretization of these equations is performed by the radial Gaussian functions centered at a system of approximating nodes. Such functions allow calculating the elements of the matrix of the discretized problem in explicit analytical form. For a regular grid of approximating nodes, the matrix of the discretized problem has the Toeplitz properties, and matrix–vector products with such matrices may be calculated by the fast fourier transform technique. The latter accelerates significantly the iterative procedure. First, the method is applied to the calculation of elastic fields in a homogeneous medium with a spherical heterogeneous inclusion and then, to composites with periodic and random sets of spherical inclusions. Simple cubic and FCC lattices of the inclusions which material is stiffer or softer than the material of the matrix are considered. The calculations are performed for cells that contain various numbers of the inclusions, and the predicted effective constants of the composites are compared with the numerical solutions of other authors. Finally, a composite material with a random set of spherical inclusions is considered. It is shown that the consideration of a composite cell that contains a dozen of randomly distributed inclusions allows predicting the composite effective elastic constants with sufficient accuracy.

Calculations of structural, elastic, electronic, and optical properties of trigonal CdI2

AbstractWe have performed ab‐initio total‐energy calculations using the plane‐wave ultrasoft pseudopotential technique based on the first‐principles density‐functional theory (DFT) to study structural parameters, elastic, electronic, chemical bonding, and optical properties of trigonal CdI2. The calculated lattice parameters and independent elastic constants are in good agreement with previous experimental works. The bulk, shear, and Young's moduli, Poisson coefficients are obtained using Voigt–Reuss–Hill method. According to the calculations of band structure, density of states and charge densities, electronic, and chemical‐bonding properties have been studied. The complex dielectric functions, refractive index, and extinction coefficient are calculated and analyzed.

First-principles calculation of structural and elastic properties of Pd 3- xRh xV alloys

The structural stability, electronic and elastic properties of Pd 3- x Rh x V alloys with L1 2 and D0 22 structures were investigated theoretically by the first-principles calculations. The results reveal that with the increase of Rh content, the unit cell volume of Pd 3- x Rh x V alloys with L1 2 and D0 22 structures decreases, and the structure of Pd 3- x Rh x V alloys tends to transform from D0 22 to L1 2. The elastic parameters such as elastic constants, bulk modulus, shear modulus, elastic modulus, and Poisson ratio, were calculated and discussed in details. Electronic structures were also computed to reveal the underlying mechanism for the stability and elastic properties.

FP‐LAPW calculations of structural and elastic properties of tantalum under high pressure

AbstractWe have revisited and refined the high‐pressure elastic properties of body‐centered‐cubic Ta using the accurate all‐electron full potential linearized augmented plane wave method (FP‐LAPW) within the framework of density functional theory (DFT). Based on the total energy calculations, we first deduced the accurate static equation of state (EOS) of Ta. Then we derived the elastic constants, C11, C12, and C44 under pressure up to 500 GPa using the pressure‐correction method which corrected the previous method theoretically, and the calculated elastic constants agree well with experiment under high pressure. From the accurately determined elastic constants, we also discussed the elastic anisotropy and the sound velocities of Ta at high pressure. The predicted Debye temperature at 0 GPa and 0 K is in good agreement with experiment, and the Debye temperature increases monotonously as pressure increases.

First-principles calculations of structural, electronic, optical and elastic properties of magnesite MgCO 3 and calcite CaCO 3

Detailed ab initio calculations of the structural, electronic, optical and elastic properties of two crystals – magnesite (MgCO 3) and calcite (CaCO 3) – are reported in the present paper. Both compounds are important natural minerals, playing an important role in the carbon dioxide cycling. The optimized crystal structures, band gaps, density of states diagrams, elastic constants, optical absorption spectra and refractive indexes dependence on the wavelength all have been calculated and compared, when available, with literature data. Both crystals are indirect band compounds, with calculated band gaps of 5.08 eV for MgCO 3 and 5.023 eV for CaCO 3. Both values are underestimated by approximately 1.0 eV with respect to the experimental data. Although both crystals have the same structure, substitution of Mg by Ca ions leads to certain differences, which manifest themselves in noticeable change in the electronic bands profiles and widths, shape of the calculated absorption spectra, and values of the elastic constants. Response of both crystals to the applied hydrostatic pressure was analyzed in the pressure range of phase stability, variations of the lattice parameters and characteristic interionic distances were considered. The obtained dependencies of lattice constants and calculated band gap on pressure can be used for prediction of properties of these two hosts at elevated pressures that occur in the Earth's mantle.

First-principles calculations of electronic structure, optical and elastic properties of LiGaX2(X=S, Se, Te)

The density of states, electronic structure, optical and elastic properties of LiGaX2 (X=S, Se, Te) are investigated by the first-principles plane-wave pseudopotential density functional theory within the generalized gradient approximation (GGA). The results show that the band gaps of LiGaX2 (X=S, Se, Te) are 4.146 eV, 3.301 eV and 2.306 eV, respectively. It can be confirmed that the valence bands are mainly composed of X-np or Ga-4p states. The complex dielectric functions, reflectivity, index of refraction and elastic property are precisely calculated by band structure and density of states. The obtained results are in agreement with the available experimental data.