Calculation Of Elastic Constants Research Articles

Modeling structural, elastic, electronic and optical properties of ternary cubic barium based fluoroperovskites MBaF3 (M = Ga and In) compounds based on DFT

This work presents in detail the Ab-initio computational research work on the structural, elastic, electronic, and optical properties of Perovskite-type (Halide-Perovskites) barium-based MBaF3 (M = Ga and In) compounds. The work is based on density functional theory (DFT) within WIEN2K. Structurally both GaBaF3 and InBaF3 based on optimization of Birch Murnaghan fit are found to be stable. The IRelast package for the calculations of elastic constants (ECs) is employed for the computation of elastic properties. Mechanically these compounds are identified to be ductile, hard to scratch, anisotropic, mechanically stable, and demonstrate strong resistance to plastic deformation. The precise modified Becke–Johnson (mBJ) potential is employed for electronic properties. Band structures of these compounds possess an insulating nature of direct wide energy band gap of 5 eV for GaBaF3 and 5.1 eV for InBaF3 from X-X symmetries points. To know the contribution of different electronic states to the band structures, the TDOS and PDOS i-e (total and partial density of states) are exploited. The insulating direct wide band gap energy nature presented a straightforward direction to study the optical properties of these compounds. The optical properties, of both the compounds, were studied deeply in the energy range from 0 eV to 40 eV. These compounds possess high absorption and optical conduction at high energy ranges. Both materials are transparent to incident photons at low energy ranges. We have concluded from the optical properties investigations that these compounds are suited for high-frequency UV device applications. To our deep knowledge, this is the first systematic theoretical computation of MBaF3 (M = Ga and In) with structural, elastic, electronic and optical, properties that have yet to be verified experimentally.

Novel Braceletlike BiSbX3 (X = S, Se) Monolayers with an In-Plane Negative Poisson's Ratio and Anisotropic Photoelectric Properties.

In this work, we predict two novel two-dimensional (2D) auxetic materials, BiSbX3 (X = S, Se) monolayers, through first-principles calculations. Attributed to their special braceletlike structure, the in-plane negative Poisson's ratio (NPR) of BiSbS3 and BiSbSe3 monolayers are as high as -0.25 and -0.26, respectively. The phonon dispersion calculations, ab initio molecular dynamics simulations, and elastic constants calculations demonstrate that these two monolayers possess excellent dynamic, thermal, and mechanical stabilities. The band gap values of BiSbS3 and BiSbSe3 calculated at the HSE level by considering the spin-orbit coupling (SOC) effect are 1.68 and 1.20 eV. The anisotropic carrier mobility and superior optical absorption indicate that they may shine in the next generation of electronic and optoelectronic devices. All of these discoveries not only enrich the types of auxetic materials but also provide a structural reference for designing new auxetic materials on the molecular level. Furthermore, they can provide theoretical guidance for future applications of BiSbX3 (X = S, Se) monolayers in various fields.

HSH-C10: A new quasi-2D carbon allotrope with a honeycomb-star-honeycomb lattice

Two-dimensional (2D) materials with honeycomb, kagome or star lattice have been intensively studied because electrons in such lattices could give rise to exotic quantum effects. In order to improve structural diversity of 2D materials to achieve unique properties, here we propose a new quasi-2D honeycomb-star-honeycomb (HSH) lattice based on first-principles calculations. A carbon allotrope named HSH-C10 is designed with the HSH lattice, and its mechanical properties have been intensively investigated through total energy, phonon dispersion, ab initio molecular dynamic simulations, as well as elastic constants calculations. Besides the classical covalent bonds, there is an interesting charge-shift bond in this material from the chemical bonding analysis. Additionally, through the analysis of electronic structure, HSH-C10 is predicted to be a semiconductor with a direct band gap of 2.89 eV, which could combine the desirable characteristics of honeycomb and star lattice. Importantly, by modulating coupling strength, a flat band near the Fermi level can be obtained in compounds HSH-C6Si4 and HSH-C6Ge4, which have potential applications in superconductivity. Insight into such mixed lattice would inspire new materials with properties we have yet to imagine.

Rational design of porous GeP2S6 monolayer for photocatalytic water splitting under the irradiation of visible light

Here, we predicted a novel compelling photocatalyst, the porous GeP2S6 monolayer. The stability of the GeP2S6 monolayer was examined via elastic constant calculations, vibratory phonon spectrum and ab initio molecular dynamics simulations. The electronic properties reveal that the GeP2S6 monolayer possesses a direct gap with the value of 2.06 eV. The photocatalytic properties analyses show that the band edges of the GeP2S6 monolayer meets the requirements of the photocatalytic decomposition water. Meanwhile, the GeP2S6 monolayer exhibits better optical absorption ability in the visible region. Additionally, high carrier mobility (electrons: 206.09 cm2/V·s and holes: 261.46 cm2/V·s) and strongly anisotropic transport properties lead to high solar energy conversion efficiency. Interestingly, the photocatalytic decomposition water in GeP2S6 monolayer is robust against compression strain, which will improve the activity of photocatalytic hydrogen evolution reaction. Our findings highlight the porous GeP2S6 monolayer as a good candidate material for electronics and photocatalytic applications.

Computational Prediction of New Series of Topological Ternary Compounds LaXS (X = Si, Ge, Sn) from First-Principles

Dirac materials and their advanced physical properties are one of the most active fields of topological matter. In this paper, we present an ab initio study of electronics properties of newly designed LaXS (X = Si, Ge, Sn) tetragonal structured ternaries, with the absence and presence of spin–orbit coupling. We design the LaXS tetragonal non-symophic p4/nmm space group (no. 129) structures and identify their optimization lattice parameters. The electronic band structures display several Dirac crossings with the coexistence of both type I and type II Dirac points identified by considering the effect of spin–orbit coupling toward the linear crossing. Additionally, we perform the formation energy calculation through the density functional theory (DFT) to predict the stability of the structures and the elastic constants calculations to verify the Born mechanical stability criteria of the compounds.

ElasTool: An automated toolkit for elastic constants calculation

We present the ElasTool package, an automated toolkit for calculating the second-order elastic constants (SOECs) of any two- (2D) and three-dimensional (3D) crystal systems. ElasTool uses three kinds of strain-matrix sets, i.e., the high-efficiency strain-matrix sets (OHESS), the universal linear-independent coupling strains (ULICS), and the all-single-element strain-matrix sets (ASESS), to calculate the SOECs automatically. ElasTool can efficiently compute both zero- and high-temperature elastic constants. We describe in detail the theoretical background and computational method of elastic constants, the package structure, the installation, and run, the input/output files, the controlling parameters, and two representative examples of how to use the ElasTool package. ElasTool is useful for either the exploration of materials' elastic properties or high-throughput new materials screening and design. ElasTool is freely available on GitHub: https://github.com/elastool Program summaryProgram Title: ElasToolCPC Library link to program files:https://doi.org/10.17632/ktvmxrdhpz.1Code Ocean capsule:https://codeocean.com/capsule/1893813Licensing provisions: GNU General Public License, version 3Programming language: Python 3External routines: NumPy [1], Spglib [2], ASE [3], Pandas [4]Nature of problem: The stress-strain method of elastic constants calculation depends on accurate stresses calculated with first-principles methods, such as the density functional theory (DFT). Compared to the energy-strain method, the stress-strain approach needs a smaller number of strain sets to solve the equation sets needed to deduce the elastic constants; it is also more straightforward to implement. However, accurate stresses take a lot of time to compute within DFT. Thus, a smaller number of strain sets and more efficient strain sets are urgently needed to improve the computational efficiency of elastic constants. An automated solution coupled with DFT is necessary for the exploration of materials' elastic properties and high-throughput new materials screening and design.Solution method: The solution to improve the computational efficiency of the stress-strain method is to decrease the number of strain-matrix sets and optimize the strain-matrix sets. We coupled our previously proposed high-efficiency strain-matrix sets (OHESS) with DFT and automated the processes of calculating the elastic tensor using the stress-strain method in the ElasTool package. ElasTool can also adopt the all-single-element strain-matrix sets (ASESS) and the universal linear-independent coupling strains (ULICS) approaches. It can deal with both zero- and high-temperature elastic constants of any crystal systems belonging to 2D or 3D. Having obtained the elastic moduli, ElasTool also gives other essential mechanical and elastic properties of materials such as Young's modulus, bulk modulus, elastic anisotropy, Debye temperature, and the sound velocities.Additional comments including restrictions and unusual features: Currently, this package interfaces with Vienna Ab initio Simulation Package (VASP) code as the stress tensors calculator. [5-7] Extension to other electronic structures is straightforward.

A novel two-dimensional boron–carbon–nitride (BCN) monolayer: A first-principles insight

The optical, electronic, and structural properties of a theoretically predicted new boron–carbon–nitride (BCN) two-dimensional monolayer have been explored using density functional theory calculations. The phonon dispersion, molecular dynamics simulation, the cohesive energy, and the Born criteria of elastic constant calculations of the BCN monolayer confirm its stability. The phonon spectrum illustrates an out-of-plane flexure mode with quadratic dispersion in the long-wavelength limit. The BCN monolayer is a semiconductor with a direct bandgap of 0.9 (1.63) eV determined via the Perdew–Burke–Ernzerhof (Heyd–Scuseria–Ernzerhof) functional. The same electron and hole effective masses and mobility values indicate the high recombination rate of electrons and holes. Meanwhile, the BCN monolayer can absorb ultraviolet radiation more effectively than visible light. Due to its interesting physical properties, the novel BCN monolayer could be a rather good candidate material for electro-optical applications.

Finite element modeling of elastic moduli and microstresses in textile carbon-carbon composites

sThe problem of detailed calculation of micro-stresses in textile composite materials under arbitrary types of loading is considered. A model for calculating the effective characteristics of textile composites considering the real complex curvilinear anisotropy of fibers in tissues is proposed. The model is based on the asymptotic homogenization method, whereby local problems of elasticity theory for a curvilinear anisotropic body are formulated. For the numerical solution of these problems, the finite element method is used. The implementation of the proposed method was carried out within the framework of the SMCM software package, developed at the Department of Computational Mathematics and Mathematical Physics of the Bauman Moscow State Technical University. The SMCM software package allows you to perform a full cycle of finite element modeling, including the stages of pre-processing and post-processing. An example of numerical modeling of a textile carbon-carbon composite of twill weaving is carried out. It is shown that the developed software package provides (a very high accuracy of calculations of the effective elastic properties of composites. The comparison was carried out with the calculations obtained using the ANSYS software, which was modified to provide the possibility of solving local problems, the relative deviation in the calculations of the effective elastic constants did not exceed (-7) degrees.

Calculation of elastic constants of embedded-atom-model potentials in the NVT ensemble

A method for the calculation of elastic constants in the NVT ensamble using molecular dynamics (MD) simulation with a realistic many-body embedded-atom-model (EAM) potential is studied in detail. It is shown that, in such NVT MD simulations, the evaluation of elastic constants is robust and accurate because it gives the elastic tensor in a single simulation which converges using a small number of time steps and particles. These results highlight the applicability of this method in (i) the calculation of local elastic constants of nonhomogeneous crystalline materials and (ii) the calibration of interatomic potentials, as a fast and accurate alternative to the common method of explicit deformation, which requires a set of consistent simulations at different conditions. The method is demonstrated for the calculation of the elastic constants of copper in the temperature range of 0-1000K, and results agree with the target values used for the potential calibration. The various contributions to the values of the elastic constants, namely, the Born, stress fluctuation, and ideal gas terms, are studied as a function of temperature.

Vacancies effect on structural, electronic and mechanical properties of delafossite CuAlO2

Delafossite-structured CuAlO2 materials with and without vacancy defects were investigated comparatively using the first principle calculation method. The method based on the density functional theory, has been carried out to search the systems’ ground states and supplies the corresponding electronic properties. In the process of calculations, ultrasoft pseudo-potentials and PBE-GGA functionals are chosen for the atoms and exchange-correlation interactons between electrons, respectively. The geometry optimization shows the Al vacancy causes a larger lattice deformation than the vacancies of Cu and O atoms. The results of Mulliken charge also verify this conclusion. The calculations of vacancy formation energy and elastic constants indicate the Cu vacancy has the lowest formation energy, the highest Pugh ratio and the smallest Zener anisotropy factor, which means the introduction of Cu vacancy can improve the functional applications of Cu-based delafossites, e.g. p-type conductivity, ductility, etc.

Effects of alloying elements on the generalized stacking fault energy of Ti5Si3: A first principle study

Influences of six alloying elements on the generalized-stacking-fault (GSF) energy in Ti5Si3 (Ti60Si36) were investigated by the first-principle methods. The GSF energy curve of Ti5Si3 (Ti60Si36) is plotted in the basal{0001}<112¯0>, prism{11¯00}[0001] and pyramidal {21¯1¯2}1/3<21¯1¯3¯>slip system after alloying with six alloying elements. According to the calculation results, the addition of alloying elements will result in a significant decrease of GSF energy, which can promote the generation of prismatic stacking defects and enhance the plasticity of Ti5Si3. In the basal {0001}<112¯0>, prism{11¯00}[0001] and pyramidal {21¯1¯2}1/3<21¯1¯3¯>slip systems, the γus of the possible slip locations decreases gradually with increasing difference in atomic size between Ti and alloying elements. At the same time, through the calculation of elastic constant, it is analyzed that the plasticity of Ti5Si3 will raise first and then fall after the addition of Al atoms with different contents. The addition of alloying elements will decrease the GSF energy, which is caused by the weakening of Ti‒Si bonds. This work may have guiding significance for the alloying design of Ti5Si3 intermetallic compounds.

Microstructural and elastic properties of stable aluminium-rich TiAl and TiAl2 formed phase Intermetallics

We studied aluminium-rich Ti-Al (Ti32Al68 and Ti40Al60) binary alloys that were composed of TiAl and TiAl2 lamellar microstructures. The law of mixtures was employed in calculating the theoretical Young’s moduli. The lattice parameters of the alloys showed that both were tetragonal crystals. In the computational study, we made use of our modified method for the stress–strain calculation of elastic constants. The alloys at the respective chemical compositions were modelled by creating titanium (Ti) supercells, which were then doped by replacing some of the Ti atoms with aluminium atoms. The values of elastic moduli were verified by the ab initio calculation in this work, which showed a perfect agreement. The Pugh’s ratio showed that both the alloys are ductile.

First principle computation of half metallicity and mechanical properties of a new series of half Heusler alloys KMnZ (Z = B, Si, Ge, As) for spintronics

In the framework of density functional theory, the first principle calculations are performed to investigate various physical properties of new series of half Heusler alloys KMnZ (Z = B, Si, Ge, As) by using WIEN2k code. The results of structural parameters show that ferromagnetic state is more stable, with Type 3, configuration than the non-magnetic and antiferromagnetic states for all KMnZ (Z = B, Si, Ge, As) compounds. All considered alloys KMnZ (Z = B, Si, Ge, As) are completely spin polarized and show half-metallic character because of the presence of band gap (BG) in minority-spin channels. The calculated magnetic moments are 3 µB, 4 µB, and 5 µB for KMnB, KMnSi (Ge), and KMnAs, respectively. The values of minority BG for KMnB, KMnSi, KMnGe, and KMnAs are 0.60 eV, 0.85 eV, 1.00 eV, and 1.20 eV, respectively. The origin of their HM gaps is also examined in addition to density of states and band structures. The Curie temperature (TC), within mean field approximation, is also calculated. The calculations for elastic constants and other mechanical parameters are computed to check the mechanical stability which revealed that all other alloys are stable with ductile nature except KMnB. From the results of several physical properties, it can be envisaged that these materials can be used for spintronic devices.

In-depth first-principle study on novel MoS2 polymorphs.

Molybdenum disulphide (MoS2) is a rising star among transition-metal dichalcogenides in photovoltaics, diodes, electronic circuits, transistors and as a photocatalyst for hydrogen evolution. A wide range of MoS2 polymorphs with varying electrical, optical and catalytic properties is of interest. However, in-depth studies on the structural stability of the various MoS2 polymorphs are still lacking. For the very first time, 14 different MoS2 polymorphs are proposed in this study and in-depth analysis of these polymorphs are carried out by employing first-principle calculations based on density functional theory (DFT). In order to investigate the feasibility of these polymorphs for practical applications, we employ wide range of analytical methods including band structure, phonon and elastic constant calculations. Three of the polymorphs were shown to be unstable based on the energy volume calculations. Among the remaining eleven polymorphs (1T1, 1T2, 1H, 2T, 2H, 2R1, 2R2, 3Ha, 3Hb, 3R and 4T), we confirm that the 1T1, 1T2, 2R2 and 3R polymorphs are not dynamically stable based on phonon calculations. Recent research suggests that stabilising dopants (e.g. Li) are needed if 1T polymorphs to be synthesised. Our study further shows that the remaining seven polymorphs are both dynamically and mechanically stable, which make them interesting candidates for optoelectronics applications. Due to high electron mobility and a bandgap of 1.95 eV, one of the MoS2 polymorphs (3Hb-MoS2) is proposed to be the most promising candidate for these applications.

On the interplay of microstructure and residual stress in LPBF IN718

The relationship between residual stresses and microstructure associated with a laser powder bed fusion (LPBF) IN718 alloy has been investigated on specimens produced with three different scanning strategies (unidirectional Y-scan, 90° XY-scan, and 67° Rot-scan). Synchrotron X-ray energy-dispersive diffraction (EDXRD) combined with optical profilometry was used to study residual stress (RS) distribution and distortion upon removal of the specimens from the baseplate. The microstructural characterization of both the bulk and the near-surface regions was conducted using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). On the top surfaces of the specimens, the highest RS values are observed in the Y-scan specimen and the lowest in the Rot-scan specimen, while the tendency is inversed on the side lateral surfaces. A considerable amount of RS remains in the specimens after their removal from the baseplate, especially in the Y- and Z-direction (short specimen dimension and building direction (BD), respectively). The distortion measured on the top surface following baseplate thinning and subsequent removal is mainly attributed to the amount of RS released in the build direction. Importantly, it is observed that the additive manufacturing microstructures challenge the use of classic theoretical models for the calculation of diffraction elastic constants (DEC) required for diffraction-based RS analysis. It is found that when the Reuß model is used for the calculation of RS for different crystal planes, as opposed to the conventionally used Kröner model, the results exhibit lower scatter. This is discussed in context of experimental measurements of DEC available in the literature for conventional and additively manufactured Ni-base alloys.

Влияние пористости слоя кремния на упругие свойства гибридных подложек SiC/Si

In this work, the influence of porosity of silicon layer with macropores on elastic and thermomechanical properties of SiC/Si substrates synthesized by the atom substitution method has been studied. Calculation of elastic constants of porous silicon has been performed by the finite element method. The results of calculation of the Young’s modulus in [111] direction are in agreement with the estimates obtained by the nanoindentation method of SiC/Si(111) substrates. The proposed theoretical model can be used for determination of elastic properties of SiC/Si substrates of different orientation.

First-principles investigations of the pressure-induced phase transformations and properties of crystalline and amorphous AlN

One-step first principles molecular-dynamics (FPMD) simulations were carried out to investigate structural transformations in wurtzite-type AlN under compression and decompression. The hexagonal transformation path $P{6}_{3}mc\text{\ensuremath{-}}P{6}_{3}/mmc\text{\ensuremath{-}}Cmmm\text{\ensuremath{-}}Fm\overline{3}m$ was identified during compression at $P=50$ GPa and $T=500$ K. The inversion of this path of transformation was established at the decompression of compressed rock-salt AlN at 1500 K. The plausible origin of these transformations is established. The occurrence of intermediate and metastable phases was predicted by taking into account their dynamical and elastic instability, and for this purpose, phonon spectra and elastic constant calculations were performed. FPMD simulations were used to generate amorphous AlN and to investigate its behavior under pressure. The sequence of phase transitions: low-density amorphous---high-density amorphous---rock-salt type was revealed at $P=40$ GPa, and the thermodynamic and mechanical properties of crystalline and amorphous AlN were compared. It was found that the one-step FPMD simulations is a viable scheme to predict phase transitions in crystalline and amorphous AlN with higher precision compared with other FPMD approaches with step-wise pressure changes.

First-principles calculation of higher-order elastic constants using exact deformation-gradient tensors

We propose a general and easy-to-use method of the ab initio calculation of the higher-order elastic constants, which is based on the analytical formulas for the deformation-gradient tensors as functions of the Lagrangian strain. The method allows for elimination of the truncation errors in the Taylor expansion series of the deformation gradients and is particularly useful to calculate the fourth-order elastic constants, where large strains have to be applied. It also facilitates the calculation of the Lagrangian stress, which is helpful in determination of the strain-stress relations. To demonstrate the application of our approach, we derive the analytic formulas for the deformation gradients as functions of the Lagrangian strain tensors, which are used in calculations of the third-order elastic constants in trigonal crystals and the fourth-order elastic constants in cubic crystals. Then, we perform the ab initio calculations of the fourth-order elastic constants in face-centered-cubic aluminum. We discuss the results obtained using the strain-energy and strain-stress relations and analyze the errors of the fourth-order elastic constants which would be incurred when approximating the deformation gradients by the Taylor polynomials. We show that the relatively small truncation errors in the Taylor expansion series of the deformation gradients can cause significant deviations of the fourth-order elastic constants. This effect is larger for the strain-energy method than for the strain-stress approach. We find that in both methods, the deviations are particularly significant for the ${C}_{1155}$, ${C}_{1266}$, ${C}_{4455}$, ${C}_{1255}$, and ${C}_{1456}$ elastic constants and are mainly caused by the truncation errors in the nondiagonal elements of the Taylor expansion series of the deformation gradients.

A new cubic superhard large-cell carbon allotrope: c-C200

A new cubic superhard large-cell carbon allotrope with 200 carbon atoms per unit cell (named c-C200) is theoretically predicted by the unbiased swarm structure searching techniques combined with the first-principles calculations. The phonon and elastic constants calculations show that c-C200 is dynamically and mechanically stable. The calculated hardness of c-C200 is 47 GPa, which means that c-C200 is a potential superhard material. The calculated electronic band structure of c-C200 shows that it is a quasi-direct band gap semiconductor with a gap of 2.781 eV.

Effects of Doped Elements (Si, Cr, W and Nb) on the Stability, Mechanical Properties and Electronic Structures of MoAlB Phase by the First-Principles Calculation.

First-principles calculations based on density functional theory (DFT) have been performed to explore the effects of Si, Cr, W, and Nb elements on the stability, mechanical properties, and electronic structures of MoAlB ternary boride. The five crystals, with the formulas of Mo4Al4B4, Mo4Al3SiB4, Mo3CrAl4B4, Mo3WAl4B4, and Mo3NbAl4B4, have been respectively established. All the calculated crystals are thermodynamically stable, according to the negative cohesive energy and formation enthalpy. By the calculation of elastic constants, the mechanical moduli and ductility evolutions of MoAlB with elemental doping can be further estimated, with the aid of B/G and Poisson’s ratios. Si and W doping cannot only enhance the Young’s modulus of MoAlB, but also improve the ductility to some degree. Simultaneously, the elastic moduli of MoAlB are supposed to become more isotropic after Si and W addition. However, Cr and Nb doping plays a negative role in ameliorating the mechanical properties. Through the analysis of electronic structures and chemical bonding, the evolutions of chemical bondings can be disclosed with the addition of dopant. The enhancement of B-B, Al/Si-B, and Al/Si-Mo bondings takes place after Si substitution, and W addition apparently intensifies the bonding with B and Al. In this case, the strengthening of chemical bonding after Si and W doping exactly accounts for the improvement of mechanical properties of MoAlB. Additionally, Si doping can also improve the Debye temperature and melting point of the MoAlB crystal. Overall, Si element is predicted to be the optimized dopant to ameliorate the mechanical properties of MoAlB.