Calculation Of Elastic Constants Research Articles

Rattling-induced suppression of thermal transport in cubic In2O3 with Sn-Ga diatomic defect

We present the first principles study of cubic In2O3 with a diatomic defect composed of a Sn atom substituting the In atom at the b-site and a Ga atom embedded in the nearest c-site (structural vacancy) with lattice positions according to the Wyckoff notations. Structural, electronic, phononic and thermal properties were investigated within density functional theory formalism. The lattice anharmonicity effects were taken into account for all possible three-phonon scattering processes. The phonon transport was considered within the Peierls-Boltzmann transport equation with relaxation time approximation. In the relaxed lattice, a strong rearrangement of the initial positions of the atoms in the defect vicinity was revealed, which primarily manifests itself in the displacement of the Sn atom toward another interstitial site. Thus, a cage is formed around the defect by 12 O and 12 In atoms. The calculations of elastic constants and mean square displacements of cage region atoms showed the rattling-like behavior of the Sn atom. Bader charge analysis and electron localization function allowed a deeper understanding and explanation of such behavior. Phonon energy spectra as compared to In2O3 and In2O3:(Sn) demonstrated flattening of phonon branches with spatial localization of phonon modes. They also revealed a decrease in average group velocities of phonons, including those of acoustic type, the presence of avoided-crossing features in the low energy range, and an increase of available phase space for three-phonon scattering. Accounting for all these vibrational features due to defect atoms resulted in a thermal conductivity drop at room temperature by more than seven times compared to In2O3.

SiC3N3 monolayer as a universal anode for alkali metal-ion batteries.

Our density functional theory calculations show that silicon doping in g-CN (SiC3N3) can improve the electrochemical performance of g-CN as an anode of alkali metal-ion batteries and solve the problems of too high adsorption ability and migration energy barrier commonly found in porous carbon nitride. The stability of SiC3N3 was verified by molecular dynamics simulations and phonon spectroscopy. Elastic constant calculations revealed that the Si doping in g-CN can improve its mechanical properties. Specifically, Li/Na/K has a suitable adsorption capability (-0.71/-0.52/-0.98 eV) and a lower migration barrier (0.73/0.43/0.21 eV) on SiC3N3, where the barrier of a single Li-ion is the lowest among the doped porous carbon nitride materials studied so far. Moreover, SiC3N3 exhibits a high theoretical capacity (253/1512/1512 mA h g-1) and a low open-circuit voltage (0.48/0.18/0.31 V) for Li/Na/K ion batteries. Compared with B-doped g-CN previously studied, Si doping can more effectively improve the electronic conductivity of g-CN owing to greater charge transfer between Si and g-CN; the migration energy barrier of alkali metal ions on SiC3N3 is reduced more significantly due to its puckered structure instead of a planar structure; and the capacity of SiC3N3 is nearly doubled for alkali metal ion batteries because it has more feasible adsorption sites for alkali metals. These results suggest that Si-doped g-CN can be a universal anode material for alkali metal ion batteries.

Full-potential KKR within the removed-sphere method: A practical and accurate solution to the Poisson equation

An efficient and accurate generalization of the removed-sphere method (RSM) to solve the Poisson equation for total charge density in a solid with space-filling convex Voronoi polyhedra (VPs) and any symmetry is presented. The generalized RSM avoids the use of multipoles and VP shape functions for cellular integrals, which have associated ill-convergent large, double-internal $L$ sums in spherical-harmonic expansions, so that fast convergence in single-$L$ sums is reached. Our RSM adopts full Ewald formulation to work for all configurations or when symmetry breaking occurs, such as for atomic displacements or elastic constant calculations. The structure-dependent coefficients ${A}_{L}$ that define RSM can be calculated once for a fixed structure and speed up the whole self-consistent-field procedure. The accuracy and rapid convergence properties are confirmed using two analytic models, including the Coulomb potential and energy. We then implement the full-potential RSM using the Green's function Korringa-Kohn-Rostoker (KKR) method for real applications and compare the results with other first-principle methods and experimental data, showing that they are equally as accurate.

Structure, half-metallic and magnetic properties of bulk and (001) surface of Rb2XMoO6 (X = Cr, Sc) double perovskites: a DFT + U study

Half-metallic (HM) ferromagnets (HM-FMs) with large HM gap and high Curie temperature (TC) have a great importance in the field of spintronics. In this study, the geometric features, electronic structure and magnetism of two new double perovskites (DPs) represented by Rb2XMoO6 (X = Cr, Sc) were explored in bulk phase and (001) surface using quantum mechanical total energy calculations based on density functional theory (DFT). The results showed that optimized lattice constant a is 7.96 Å and 8.26 Å for Rb2CrMoO6 (RCMO) and Rb2ScMoO6 (RSMO), respectively, in the cubic phase (space group Fm-3m, #225). The cohesive energy Ecoh, formation energy Efor and elastic constants (mechanical) calculations proved that present materials are stable. The magnetic properties were explored in terms of ground state magnetic coupling, total magnetic moment (M) and atomic magnetic moment (m), exchange energy (J), and Curie temperature. It was found that both materials have ferromagnetic coupling in the ground state, with M of integer value of 8.0 μ B (4.0 μ B), J value of 47 meV(72 meV) and TC of 365 K (557 K) in Rb2CrMoO6 (Rb2ScMoO6). The electronic properties computed with electronic band structure and density of states demonstrated both DPs to be half-metal with HM gap of 1.61 eV (2.1 eV) in Rb2Cr-based (Rb2Sc-based) system. Finally the electronic and magnetic properties of (001) surfaces were investigated and compared with that of bulk phase. Interestingly, bulk HM property was retained in RSMO, but disappeared in RCMO due the emergence of defect states at Fermi level (EF). The reported results suggest that Rb-based DPs carry some fascinating properties for spin-based devices.

The structural, mechanical and electrical properties of 2D SiC with C-related point defects and substitution of C by foreign atoms

As a wide and direct bandgap semiconductor material, two-dimensional (2D) graphene-like SiC has attracted extensive research attention recently. Native defects and foreign impurities often have remarkable effects on the properties of semiconductors. In this paper, the structural, mechanical and electrical properties of 2D SiC with carbon antisite (CSi), vacancy (VC), interstitial (Ci) and substitution of C by N (NC) and B (BC) have been studied systematically using first-principles calculations. It is found that defects do not cause structural reconstruction for 2D SiC. The formation energies of CSi, VC, NC and BC are not sensitive to the uniaxial strain. CSi and Ci are likely to be formed spontaneously due to the negative formation energy values. In addition, the phonon spectra and elastic constant calculations show that the properties of 2D SiC with VC and Ci are unstable. Furthermore, from the calculations of the band structures and density of states, we observed that the bandgap of 2D SiC is slightly reduced by CSi, VC, Ci, and NC, however is increased by BC. Prominent additional charge states are generated in the bandgap of 2D SiC except for NC. Moreover, the overall carrier mobility of 2D SiC could be significantly reduced by the defects.

Quantitative texture analysis at the WAND2 and HIDRA diffractometers

Data collection and analysis strategies have been developed for efficient and reliable crystallographic texture measurements at two recently upgraded neutron diffractometers: the Wide Angle Neutron Diffractometer Squared (WAND2) and the High Intensity Diffractometer for Residual Stress Analysis (HIDRA) at the High Flux Isotope Reactor located at Oak Ridge National Laboratory. These methods are demonstrated using measurements on a variety of textured samples, including multi-phase steel composites and polycrystalline calcite (CaCO3). Reference measurements were also made at VULCAN, the engineering diffractometer located at the Spallation Neutron Source. The texture data obtained on the different instruments are in agreement, and WAND2 is more time efficient than HIDRA. Two analysis methods were investigated, single-peak fitting to obtain individual pole figures for inversion and Rietveld texture analysis using MAUD. The impact of the differences between the various textures obtained was evaluated through the calculation of diffraction elastic constants, which is one application of the texture data collected. Both instruments were found to provide texture data that are suitable for complementing other analyses, such as residual stress mapping.

Effect of hydrostatic pressure on mechanical and optoelectronic properties of ACuO3 (A = Ca, Sr)

We investigate the hydrostatic pressure dependences of elastic, electronic, and optical properties of the newly hypothesized perovskite compound ACuO3 (A = Ca, Sr) using the first-principles method. The structural and mechanical stabilities have been established theoretically under pressure up to 100 GPa. The ductile nature of these transition metal oxides has been confirmed by the calculation of elastic constants. The relatively low-value Young’s modulus possesses high thermal shock resistance and proclaims the materials to be a promising thermal barrier coating material. The partial density of states shows the dominant behavior of Cu-3d and O-2p orbitals at the Fermi level and it implies the subsequent good electrical conductivity. The significant response of the optical properties such as reflectivity, dielectric constant, optical absorption, and loss function with the change in pressure have been noted. The origin of these optical responses is discussed with implications, which can be supportive for future investigations of ACuO3 (A = Ca, Sr).

The electronic, mechanical properties and in-plane negative Poisson’s ratio in novel pentagonal NiX2 (X = S, Se, Te) monolayers with strong anisotropy: A first-principles prediction

Inspired by the groundbreaking discoveries of the transition metal dichalcogenides (TMDCs) materials, the structural stabilities, electronic and mechanical properties of the pentagonal NiX2 (X = S, Se, Te) monolayers were comprehensively investigated by the first-principles calculations. The NiS2, NiSe2, and NiTe2 monolayers are indirect semiconductors with bandgaps of ∼ 2.45, ∼ 2.31 and ∼ 1.88 eV by using the HSE06 functional. The elastic constant and phonon dispersion calculations show that the pentagonal NiX2 (X = S, Se, Te) monolayers are mechanically and dynamically stable without negative values in elastic constant and frequency. Ab initio molecular dynamics (AIMD) simulations demonstrate the thermal stabilities of pentagonal NiX2 (X = S, Se, Te) monolayers at 300 K and 600 K, as evidenced by the unnoticeable structural evolutions and slightly changes in total energy. The negative Poisson’s ratio (NPR) is discovered for the NiTe2 monolayer, and the authenticity is analyzed by the unique geometric structure, electronic properties and bonding characteristics, which further expands the potential application of the pentagonal NiTe2 monolayer with auxetic effect. Our present work would not only provide a fundamental understanding of structural stabilities, electronic and mechanical properties of the pentagonal NiX2 (X = S, Se, Te) monolayers, but also shed some light on the experimental investigation on the pentagonal NiTe2 monolayer with novel auxetic effect.

An Improved Artificial Neural Network Elastic Constant Prediction Method Based on Particle Swarm Optimization

As machine learning methods keep developing in materials science, using machine learning to mine novel materials has become a research hotspot. For microscopic crystals, the first-principles calculation of elastic constants has always been a conventional research method. However, the first-principles calculation method is time-consuming and laborious, which limits the development of materials. In order to achieve efficient discovery of new materials, this paper proposed an improved artificial neural network (ANN) method to predict the elastic modulus of crystals improved by particle swarm optimization (PSO), which build the PSO-ANN model in use of structures and elastic constants of crystals. Experiments show that the root mean square error (RMSE) can reach within 1GPa. To verify the accuracy of the method for other crystal predictions, the MgZn2 crystal is modelled and calculated by using the first-principles calculation method. Comparing with the prediction method proposed, the average error of the predicted elastic constants is within the range 5.6%.

Pressure effect on the halide double perovskite Cs2TlBiCl6; Ab initio study

Motivated by its potential solar cell applications, we investigated the mechanical, electronic, and optical properties of the double halide perovskite Cs2TlBiCl6 in the cubic Fm3‾m phase using first-principles calculations. The obtained lattice parameters of the cubic structure are in good agreement with previous results. The thermodynamic stability of the system from the cohesive energy and the formation energy. Also, from the elastic constants calculations, we confirmed the mechanical stability of this material for cubic symmetry. The calculated B/G ratio and Poisson's ratio show that the Cs2TlBiCl6 system has a ductile nature and strong ionic bonds. The TB-mBJ potential was used to calculate the electronic and optical properties. The Cs2TlBiCl6 system showed a direct band gap that is in the visible region but the absorption is weak in the same region. By applying pressure, we found an increase and shift in the absorption spectrum in the visible region. This finding indicates that the Cs2TlBiCl6 system can be considered as potential candidate for solar cell applications.

Phase stability, mechanical, and thermal properties of high‐entropy transition and rare‐earth metal diborides from first‐principles calculations

AbstractThe narrow composition design space of high‐entropy transition metal diborides (HE TMB2) limits their further development. In this study we designed six quaternary and quinary high‐entropy transition metal and rare‐earth diborides (HE TMREB2) and investigated their phase stability using the energy distribution of the local mixing enthalpy of all possible configurations. The results show that both quaternary and quinary HE TMREB2 have higher enthalpic driving forces, which facilitates the formation of single‐phase AlB2‐type structures between TMB2 and REB2. Calculations of elastic constants show that the TMB2 component has the greatest effect on the c44 elastic constant and shear modulus G, while REB2 significantly influences the bulk modulus B. Furthermore, LuB2 and TmB2 substantially affect the elastic modulus anisotropy of HE TMB2. Rare‐earth atoms in HE TMREB2 can enhance the nonharmonic interactions between phonons, which results in a significant hindrance in the thermal transport of low‐frequency phonons as well as an increase in the volume thermal expansion coefficients. Thus, the incorporation of REB2 into HE TMB2 has a significant impact on the phase stability and properties.

New insights into the mechanical and thermal properties of UN1-xCx from first-principles calculations

Uranium nitride (UN) is considered to be a very promising candidate of accident-tolerant fuel. Since UN is commercially synthesized by carbothermic reduction-nitridation, the carbon in synthesized UN is unavoidable. Interestingly, UN1-xCx solid solutions obtained by isothermal conversion exhibit some more excellent properties, such as corrosion resistance. But the effect of composition on the mechanical and thermal properties is not clear yet. In this work, first-principles calculations were carried out to investigate the stabilities, mechanical and thermal properties of UN1-xCx (x = 0.00, 0.25, 0.50, 0.75 and 1.00). The impact of the on-site Coulomb repulsion term and spin-orbit coupling (SOC) on the properties of UN1-xCx were also discussed. The on-site Coulomb repulsion term is indispensable for the magnetic ground state, mechanical and thermal transport properties. Moreover, SOC has a negligible influence on the mechanical properties and can overestimate the thermal conductivities of UN1-xCx. Formation enthalpy, phonon dispersion and elastic constants calculations were preformed to prove the thermodynamic, dynamic and mechanical stability of UN1-xCx, respectively. The absence of a band gap in the density of states confirms the metallic nature of studied UN1-xCx. Theoretical analyses show that large-size carbon doping can induce lattice expansion and softening, resulting in the reduction of elastic moduli. The more localized density of states of UN1-xCx with carbon concentration demonstrate the weaker bond strength, which further verifies the variation of mechanical properties. The thermal conductivities of UN1-xCx calculated using PBE+U decrease firstly, then increase with the carbon concentration and increase with the temperature.

Effect of 5d state-based full-Heusler alloys on the structural, electronic and magnetic properties of new half metallic ferromagnetism

First-principles calculations of structural, elastic, electronic and magnetic properties of full-Heusler Ir2HfB, Ir2HfAl and Ir2HfGa have been realized by full-potential linearized augmented plane wave (FP-LAPW) method implemented inWIEN2K code. The Perdew–Burke–Ernzerh of generalized gradient approximation (PBE-GGA) carried out the computation of different parameters to describe elastic and structural properties. The calculation of structural properties revealed that the three alloys are stable in cubic AlCu2Mn-type structure in ferromagnetic state. The elastic constants calculation shows the three alloys satisfy the stability criteria. Indeed, the calculated spin-polarized electronic band structure and density of states using generalized gradient approximation (GGA) show that Ir2HfZ (Z = B, Al, Ga) alloys have a metallic character. The influence of strong electronic correlation has been considered in GGA+Uand mBJ-GGA+U approximations that allows for improving the width of the band gap. The calculations carried out with GGA+U and mBJ-GGA+U show that Ir2HfAl and Ir2HfGa have a half-metallic behavior; however, Ir2HfB has a near half-metallic character. The calculated magnetic moments of Ir2HfB, Ir2HfAl and Ir2HfGa in a regular cubic structure with GGA+U and mBJ-GGA+U equal 1μB. With mBJ-GGA+U, the spin polarization values are 100% for Ir2HfAl, Ir2HfGa and 99.90% for Ir2HfBto be applicable for spintronics.

MyElas: An automatized tool-kit for high-throughput calculation, post-processing and visualization of elasticity and related properties of solids

Elasticity is one of the most fundamental mechanical properties of solid. In high-throughput design of advanced materials, there is an imperative demand for the capability to quickly calculate and screen a massive pool of candidate structures. A fully automatized pipeline with minimal human intervention is the key to provide high efficiency to achieve the goal. Here, we introduce a tool-kit MyElas that aims to address this problem by forging all pre-processing, elastic constant and other related property calculations, and post-processing into an integrated framework that automatically performs the assigned tasks to drive data flowing through parallelized pipelines from input to output. The core of MyElas is to calculate the second and third order elastic constants of a solid with the energy-strain method from first-principles. MyElas can auto-analyze the elastic constants, to derive other related physical quantities. Furthermore, the tool-kit also integrates a visualization function, which can, for example, plot the spatial anisotropy of elastic modulus and sound velocity of monocrystalline. The validity and efficiency of the toolkit are tested and bench-marked on several typical systems. Program summaryProgram title: MyElasCPC Library link to program files:https://doi.org/10.17632/jbz2s9xsmv.1Code Ocean capsule:https://codeocean.com/capsule/4149434Licensing provisions: GNU General Public License 3Programming language: Python 3.XExternal routines/libraries: Numpy [1], Spglib [2], Matplotlib [3]Nature of problem: Through the first-principal calculation, the second-order and third-order elastic constants of solid materials are automatically calculated, and the post-processing and visualization of single crystal and polycrystalline physical properties are carried out.Solution method: Firstly, the required strain structure is automatically generated through the space group of materials and the corresponding strain matrix. Secondly, the energy of the structure is calculated by first-principles calculation software such as VASP [4]. Thirdly, the relationship between energy and strain is polynomial fitted to deduce the elastic constant of the material. Fourth, automatically derive the relevant physical properties. Finally, the distribution of mechanical modulus and sound velocity in spherical space is visualized.Additional comments including restrictions and unusual features: Many modules of the software can be embedded into other software through simple modification, such as visualization module. The software supports finite temperature calculation with electronic temperature. In addition, the software supports the derivation of corresponding elastic constants from phonon spectrum data generated by Phonopy [5], Alamode [6] and TDEP [7] software through long-wave limit approximation and Christoffel equation.

Unravelling the regulating role of stacking pattern on the tunable dipole, mechanical behavior and carrier mobility for asymmetric Janus SnSSe bilayer

Recently, Janus two-dimensional (2D) materials have attracted considerable interest because of the novel physical properties in view of reducing dimensionality and breaking reflection symmetry. With the help of first-principles calculations, the structural and mechanical, electronic structure and vertical dipole, and carrier mobility of SnSSe bilayer with different stacking patterns were comprehensively evaluated in this study. The calculations of binding energy and elastic constants demonstrate the experimental feasibility of SnSSe bilayer configurations with different stacking patterns. The bandgaps of SnSSe bilayer configurations can be regulated in the range of ~ 0.50 to ~ 0.75 eV due to the diversity of stacking patterns. Non-zero dipole moments induced built-in electric fields are found in SSnSe/SSnSe configurations, which unravels the dependence of the dipole moments on thickness and different stacking patterns. Additionally, the calculated carrier mobilities of SnSSe bilayer exhibits anisotropy and stacking pattern dependence, and the electron mobility can reach up to ~ 8513.63 cm2/V·s along the y-direction. Our present work would not only provide fundamental understanding of stacking dependence of dipole moment, mechanical behavior, and carrier mobility on asymmetric SnSSe bilayer, but also shed some light on the theoretical design of Janus SnSSe material within electronic, optoelectronic and thermoelectric applications.

Molecular dynamics analysis of elastic properties and new phase formation during amorphous ices transformations

Unlike conventional first-order phase transitions, the kinetics of amorphous-amorphous transitions has been much less studied. The ultrasonic experiments on the transformations between low-density and high-density amorphous ice induced by pressure or heating provided the pressure and temperature dependencies of elastic moduli. In this article, we make an attempt to build a microscopic picture of these experimentally studied transformations using the molecular dynamics method with the TIP4P/Ice water model. We study carefully the dependence of the results of elastic constants calculations on the deformation rates. The system size effects are considered as well. The comparison with the experimental data enriches our understanding of the transitions observed. Our modeling gives new information about the formation mechanisms of new phase clusters during the transition between low-density and high-density amorphous ices. We analyse the applicability of the term “nucleation” for these processes.

Accurate Ab-initio calculation of elastic constants of anisotropic binary alloys: A case of Fe–Al

The final formed phases of alloys are functions of the chemical compositions of the mixture. The overall mechanical moduli of the alloy are also functions of the phases present. Most of the previous computed elastic constants of multi-phase alloys have showed a significant deviation from the experimental values. In this study, we present a detailed analysis and verification of the experimental elastic constants of a dual-phase ferro aluminide alloys by applying both the method of mixtures and directional elastic moduli in order to obtain the match between the experimental and computational values. The computational study was done using density functional theory as implemented in the quantum espresso code. The anisotropic Young's moduli of the alloys were determined along specific directions. The values along the (1 0 0) direction, combined with application of method of mixtures, were found to be in very good agreement with those from the previous experimental studies.

Structural, Elastic, Electronic, Magnetic, and Thermoelectric Properties of the IrFeSi Half-Heusler Compound: A First-Principles Study

The emerging need for new functional materials has recently been engaged in a large quest to predict the alternative green and low-cost energy industry. To this end, thermoelectric as well as spintronic applications remain challenging. In this study, we present, for the first time, a density functional calculation on the IrFeSi half-Heusler compound. The calculation gives a deep analysis of the stability within the calculation of phonon spectra and elastic constants as well as Gibbs energy. The electronic and magnetic properties show that the investigated compound is a half-metallic ferromagnetic material. We show that IrFeSi has an integer magnetic moment of 3[Formula: see text][Formula: see text] in good agreement with the Slater–Pauling (SP) rule. By means of the Boltzman theory, we find that the investigated compound exhibits an interesting thermoelectric performance at room temperature.

Molecular Simulation Approaches to the Study of Thermotropic and Lyotropic Liquid Crystals

Over the last decade, the availability of computer time, together with new algorithms capable of exploiting parallel computer architectures, has opened up many possibilities in molecularly modelling liquid crystalline systems. This perspective article points to recent progress in modelling both thermotropic and lyotropic systems. For thermotropic nematics, the advent of improved molecular force fields can provide predictions for nematic clearing temperatures within a 10 K range. Such studies also provide valuable insights into the structure of more complex phases, where molecular organisation may be challenging to probe experimentally. Developments in coarse-grained models for thermotropics are discussed in the context of understanding the complex interplay of molecular packing, microphase separation and local interactions, and in developing methods for the calculation of material properties for thermotropics. We discuss progress towards the calculation of elastic constants, rotational viscosity coefficients, flexoelectric coefficients and helical twisting powers. The article also covers developments in modelling micelles, conventional lyotropic phases, lyotropic phase diagrams, and chromonic liquid crystals. For the latter, atomistic simulations have been particularly productive in clarifying the nature of the self-assembled aggregates in dilute solution. The development of effective coarse-grained models for chromonics is discussed in detail, including models that have demonstrated the formation of the chromonic N and M phases.

Enhancing efficiency and scope of first-principles quasiharmonic approximation methods through the calculation of third-order elastic constants

A novel computational strategy is presented to calculate from first principles the coefficient of thermal expansion and the elastic constants of a material over meaningful intervals of temperature and pressure. This strategy combines a novel implementation of the quasiharmonic approximation to calculate the isothermal-isochoric linear and nonlinear elastic constants of a material, with elementary equations of nonlinear continuum mechanics. Our implementation of the quasiharmonic approximation relies on finite deformations, the use of nonprimitive supercells to describe a material, a recently proposed technique to calculate generalized mode Gr\"uneisen parameters, and the numerical differentiation of the stress tensor to calculate both second- and third-order elastic constants. The combination of this method with nonlinear continuum mechanics is shown to yield accurate predictions of lattice parameters and linear elastic constants of a material over finite intervals of temperature and pressure, at the cost of calculating isothermal second- and third-order elastic constants for a single reference state. Here, the validity and limits of our novel methods are assessed by carrying out calculations of MgO based on classical interatomic potentials. To demonstrate potential, our methods are then used in conjunction with a density functional theory approach to calculate thermal expansion and elastic properties of silicon, lithium hydrate, and graphite.