Calculation Of Elastic Constants Research Articles

Structural, mechanical and thermodynamic stability of the CaIn intermetallic compound for promising hydrogen storage: ab-initio calculations

This study was conducted to investigate the structural, elastic, dynamical, mechanical, and thermodynamic properties of the binary intermetallic compound CaIn in various crystallographic phases, utilizing density functional theory (DFT) calculations. The results reveal that the compound is chemically and mechanically stable, as indicated by the formation energy, stability in the phonon dispersion, and elastic constants calculation. The mechanical and thermodynamic properties of our studied compound are only examined in the most stable calculated phase, which is the orthorhombic phase (Pmma). By calculating Pugh’s ratio it has been determined that this compound possesses a brittle character. The quasi-harmonic Debye (QHD) model was employed to analyze various thermodynamic parameters such as Debye temperature, volume variation, isothermal bulk modulus, heat capacity, and thermal expansion coefficient. These findings are expected to encourage further theoretical and experimental studies on the CaIn intermetallic compound for potential applications as a hydrogen storage material and in various other fields.

Structural, electronic, optical and elastic properties of Mg3TH7 (T=Mn, Tc and Re) complex hydrides: First-principles calculations

The structural, electronic, optical and elastic properties of Mg3TH7 (T=Mn, Tc, Re) complex hydrides have been investigated by using the density functional theory ‘DFT’ within the generalized gradient approximation ‘GGA’ parameterized by the Perdew, Burke and Ernzerhof ‘PBE’. The optimized lattice constants, atomic positions and interatomic distance are in good agreement with both theoretical results and experimental data available in the literature. Band structure, densities of states ‘DOS’, optical properties, and elastic constants have been calculated. The obtained results of elastic properties were compared with those of the simplest Mg-based hydride MgH2. More importantly, it is found that, the energy band gap is highly augmented when Mn atom is replaced by Re, but it is less pronounced when Re atom is replaced by Tc. From elastic constants calculations, it is noted that MgH2, Mg3MnH7, Mg3TcH7 and Mg3ReH7 compounds are mechanically stable and are brittle. In addition, the polycrystalline elastic properties such as bulk modulus, shear modulus, Young modulus and Poisson’s ratio were also determined by the Voigt-Reuss-Hill, ‘VRH’ approximation. It was found that the bulk modulus of complex hydrides Mg3TH7 (T=Mn, Tc and Re) are higher than that of MgH2 and increases with increasing atomic number of element (Mn, Tc, Re) in the sequence (B) Mg3MnH7 < (B) Mg3TcH7 < (B) Mg3ReH7. The shear anisotropy, linear bulk modulus and percentage anisotropy in compressibility and shear were also determined and discussed in details. Finally, Debye temperatures were calculated and discussed.

Effect of vacancies on structural, electronic, elastic, and thermoelectric properties of CdIn[formula omitted]Se[formula omitted] defect chalcopyrite-type semiconductor: An ab-initio approach

In this work, we have investigated the detailed structural, electronic, elastic, mechanical and thermoelectric properties of pure (CdInSe2) and defect (CdIn2Se4) chalcopyrite-type semiconductors using the ab-initio approach within the density functional theory along with semi-classical Boltzmann transport theory. The structural properties reveal the pure structure is more distorted than the defect one. The electronic band structure infers that the pure structure is an n-type semiconductor while the defect one is an intrinsic semiconductor having a larger bandgap as compared to the former due to the cationic vacancy. Both compounds are direct bandgap semiconductors. From the calculation of elastic stiffness constants and elastic moduli, it is found that both the compounds are mechanically stable. The melting temperature of CdInSe2 and CdIn2Se4 are obtained as 831 K and 784 K, respectively. The electronic thermoelectric properties show a higher value of ZT = 0.86 for the ordered vacancy compound (CdIn2Se4) with a fixed hole concentration of 1020 cm−3 at 800K making it competent for the thermoelectric applications. The variation of various thermoelectric coefficients w.r.t. the chemical potential shows that in CdIn2Se4, the p-type doping is favorable to further enhance the thermoelectric behavior. The lattice thermal conductivity for the defect structure is found to be 3.78 W/mK at room temperature and a lowest value of 1.421 W/mK at 800K. The results demonstrate the defect CdIn2Se4 as a promising thermoelectric material.

Study of the physical aspects of Pt3T (T = Mn, Ni) intermetallic compounds using first principles method

Platinum based transitional intermetallic compounds creates significant interest in the research area because of having their promising physical, optical, and electronic properties with the large scale of thermodynamic applications. The main purpose of this study is to examine the several physical properties of intermetallic compounds Pt3T (T = Mn, Ni) explored through density functional theory (DFT). The reliability of this work was made by comparing the investigated mechanical features with previously studied compounds of similar types. The calculated structural parameters have a similarity with experimental values. For the first time, we have calculated as well as presented the elastic constants, Cauchy pressure, bulk, shear, and Young's moduli. The mechanical stability of these compounds is proven by the calculation of elastic constants which meets necessary stability requirements. Metallic and ductile nature of Pt3Mn and Pt3Ni is represented by the Cauchy pressure and Pugh's ratio respectively. High machinability index of Pt3Ni ensured its low friction and huge application in industry. Band structure and DOS calculations also represented the metallic behavior of these compounds. High reflectivity in UV region refers the high conductance characteristics of Pt3T (T = Mn, Ni) in low energy regions. Very high absorption in the UV region is observed here. In the infrared region high refractive index is noticed. The dielectric constant's ε1(ω) large negative value in the real part demonstrates the Drude-like behaviors which are the metallic system's common characteristics. Very high melting temperature of Pt3T (T = Mn, Ni) ensured their probable applications in the high temperature technology. TBC nature of these phases has been ensured from their very low thermal conductivity values.

Design and characterization of novel 2D TlPt2X3 (X = S, Se, Te) semiconductor monolayers for electronic and optoelectronic applications

The energy crisis and environmental issues have stimulated an increasing interest in developing novel materials, such as two-dimensional (2D) materials, with customized photocatalytic and photovoltaic features for sustainable energy production. In this study, we thoroughly investigated the stability, physical characteristics, electronic properties, optical behaviors, and photocatalytic potential of TlPt2X3 (X = S, Se, Te) monolayers (MLs) using state-of-the-art density functional theory calculations at HSE06 and PBE-GGA levels of theory. Our calculations show that these MLs are dynamically, thermally, mechanically, and thermodynamically stable. The elastic constant calculations indicate that these MLs possess high mechanical flexibility owing to their small Young's modulus. The HSE06 approach calculations reveal that the TlPt2S3, TlPt2Se3, and TlPt2Te3 MLs possess band gaps of 1.364 eV (indirect), 1.896 eV (indirect), and 1.174 eV (direct), respectively. The optical characteristics of these MLs demonstrate a wide absorption spectrum that can be activated by visible light, with considerable absorption intensity in the near ultraviolet range. Our findings demonstrate that the TlPt2Se3 (TlPt2Te3) ML exhibits remarkable hydrogen-oxygen (oxygen) evolution performance with an increase (decrease) in pH value, suggesting they can be used for photocatalytic water splitting under visible light. These results provide new directions for the use of these materials in photocatalytic water splitting and optical devices.

Effect of Dehydroxylation on Tribological Performances of Synthetic Magnesium Silicate Hydroxide as Lubricant Additive

Abstract The heat-treated nanoparticle heat-treated magnesium silicate hydroxide (MSHH) was obtained based on the synthesis of lamellar nanoparticle magnesium silicate hydroxide (MSH) and analysis of thermal stability, and the morphology, phase composition, and chemical groups of nanoparticles were subsequently characterized. The heat treatment process induces partial dehydroxylation of MSHH, while preserving the layered structure. Compared with MSH, the tribological performances of MSHH as a lubricant additive have been greatly improved. The mechanical properties of MSH and MSHH are analyzed by calculation of elastic constants using density functional theory (DFT). The interactions among dispersant oleic acid (OA), nanoparticles (MSH and MSHH), and Fe tribopairs were investigated by simulations of classical molecular dynamics (CMD) from the views of adsorption energy and confined shear. The tribological mechanism of MSHH as a lubricant additive is proposed based on the decreased shear strength and weakened agglomeration.

Mechanical Properties of Al–Mg–Si Alloys (6xxx Series): A DFT-Based Study

Al–Mg–Si alloys are used in aircraft, train, and car manufacturing industries due to their advantages, which include non-corrosivity, low density, relatively low cost, high thermal and electrical conductivity, formability, and weldability. This study investigates the bulk mechanical properties of Al–Mg–Si alloys and the influence of the Si/Mg ratio on these properties. The Al cell was used as the starting structure, and then nine structures were modeled with varying percentages of aluminium, magnesium, and silicon. Elastic constant calculations were conducted using the stress–strain method as implemented in the quantum espresso code. This study found that the optimum properties obtained were a density of 2.762 g/cm3, a bulk modulus of 83.3 GPa, a shear modulus of 34.4 GPa, a Vickers hardness of 2.79 GPa, a Poisson’s ratio of 0.413, a Pugh’s ratio of 5.42, and a yield strength of 8.38 GPa. The optimum Si/Mg ratio was found to be 4.5 for most of the mechanical properties. The study successfully established that the Si/Mg ratio is a critical factor when dealing with the mechanical properties of the Al–Mg–Si alloys. The alloys with the optimum Si/Mg ratio can be used for industrial applications such as plane skins and mining equipment where these properties are required.

A comparative investigation on the fundamental physical properties of UX2 (X = O, N, C, Si and S) solid nuclear fuel materials: A DFT + U study

This study investigates and compares the physical properties of various UX2 (X = O, N, C, Si and S) nuclear fuels using a combination of Density Functional Theory (DFT) and Hubbard U correction parameter (U) to accurately model the electronic structure and account for strong correlation effects among 5f orbital electrons. Spin-polarized DFT + U method is employed to optimize the structures of the considered compounds. The computational analysis reveals that UO2 and UN2 exhibit Mott-insulating properties, while the remaining UX2 compounds demonstrate metallic nature. To assess the mechanical aspects of these materials, the study evaluates their mechanical stability, Vickers hardness and machinability index through calculations of elastic constants. Notably, all the UX2 fuels are found to be mechanically stable and possess ductility. Both the two-dimensional (2D) and three-dimensional (3D) depictions of the elastic moduli for the analyzed solid fuels demonstrate the presence of elastic anisotropy. The famous Slack's equation is used to determine the lattice thermal conductivity of the UX2 fuels, providing valuable insights into their thermal properties. Among the investigated materials, UC2 exhibits the highest values of Debye temperature and lattice thermal conductivity, which amount to 412 K and 15.73 Wm−1 K−1 at 300 K, respectively. Furthermore, UN2 demonstrates the highest melting temperature. Among the compounds under investigation, UC2 and UN2 fuels exhibit the most minimal thermal expansion and the greatest heat capacity. Based on these findings, UC2 and UN2 emerge as promising alternative fuel materials to UO2 for potential use in nuclear power reactors. This research contributes to the ongoing efforts in identifying alternative fuel materials.

Study on the electronic structures, mechanical properties, and lithium-ion migration of Mo-N co-doped LiFePO4 by first-principles

This article uses first principles to calculate the mechanical stability, electronic structure, and electrochemical performance of Mo-N co-doped LiFePO4. The formation energy of Mo-N co-doped LiFePO4 indicates excellent thermodynamic stability. Electron density of states and effective electron mass calculations demonstrate that co-doping can enhance the electrical conductivity of the system. The de-lithium calculations show that doping the material with Mo-N enhances its cyclic stability. Elastic constant calculations demonstrate that the dopants can enhance the shear resistance and de-lithium capacity of LiFePO4. Additionally, investigations on the material's anisotropy have revealed that Mo-N co-doping tends to promote isotropy in the material. The decrease in the migration barrier of the doped system indicates that co-doping increases the migration rate of lithium ions, thereby enhancing the rate performance of the material.

First-principles investigations for the hydrogen storage properties of XVH3 (X=Na, K, Rb, Cs) perovskite type hydrides

The structural, mechanical, electronic, kinetic, thermodynamic, optical and hydrogen storage properties of new perovskite hydrides XVH3 (X = Na, K, Rb, Cs) were investigated using density functional theory (DFT). The calculation of formation energy and elastic constants shows that the XVH3 compounds have thermodynamic and mechanical stability. The calculation of the B/G ratio revealed that these hydrides are brittle materials. Furthermore, the bonding type of these hydrides was found to be closer to ionic bonding. These compounds were found to be insulators with ferromagnetic properties in terms of their electronic properties. Furthermore, Bader partial charge analysis was utilized to investigate their charge transfer properties. The optical properties analysis demonstrated that these hydrides exhibit high absorption rates in ultraviolet region. The dynamic stability of these crystals was determined by analyzing their phonon dispersion curves, also their thermodynamic properties, including heat capacity, entropy, energy and free energy as a function of temperature, were studied. Furthermore, this study investigated the hydrogen storage capacity of XVH3 compounds. The results indicated that NaVH3, KVH3, RbVH3 and CsVH3 had hydrogen storage capacities of 3.78, 3.15, 2.12 and 1.59 wt%, respectively. This study is the first to explore XVH3 perovskite hydrides and provides new potential hydrogen storage material options.

A comprehensive DFT study on the physical properties of XCrAl (X= Fe, Co, Ni, Cu) half-Heusler alloys for applications in high-temperature technology

In the present work, structural, electronic, magnetic, elastic, mechanical, thermal and optical properties of XCrAl (X = Fe, Co, Ni, Cu) Half-Heusler (H–H) alloys were explored. First-principles study based on the non-polarized and spin-polarized density functional theory (DFT) were employed to get the geometrically relaxed unit cell structures of H–H alloys of investigation. The larger lattice constant values were found due to the spin polarization and the magnetic moments were calculated from the spin density of states (DOS). The higher values of magnetic moments make XCrAl alloys suitable for magnetic device applications. The computational electronic structure analyses at zero applied pressure confirm the zero energy band gap of XCrAl alloys which displayed metallic nature for all the compounds. From the elastic constants calculations, all the studied alloys were found mechanically and thermally stable. The values of melting temperatures were obtained in the range from 2072 to 1883 K and the calculated Debye temperatures followed the same manner of variation. Among the studied compounds, FeCrAl exhibits highest melting temperature and lattice thermal conductivity with the value of 12.94 Wm−1K−1 at 300 K which is in good agreement with the other reported results. These investigations suggest that, FeCrAl is relatively more suitable in accident-tolerant fuel (ATF) cladding material applications over the common Zr-based cladding rods. The frequency dependent optical properties of the studied H–H alloys were also explored comprehensively and the examinations indicate that, XCrAl (X = Fe, Co, Ni, Cu) alloys can also be the good choice for ultraviolet (UV) based optical device applications as they have high absorption coefficient of >200 × 104 cm−1 and maximum reflectivity of >94% in the UV region.

First-principles calculations to investigate structural, electronics, mechanical, and optical properties of KGaO3 cubic perovskite for photocatalytic water-splitting application

A first-principles investigation has been used to construct the crystal structure with space group 221 that has cubic nature developed in CASTEP software. A pseudo-potential plane-wave technique inside the GGA (generalized-gradient-approximation) and PBE (Perdew-Burke-Ernzerhof) exchange-correlation functional are used to investigate the KGaO3 compound. The present research report is on the structural, electronics, mechanical, and optical properties of KGaO3. The electronic properties reveal that the material is semi-conductor and has indirect band gap of 2.74 eV which reduce the electron-holes recombination. The elastic constant values were also investigated and utilized to investigate mechanical parameters such as shear modulus, Young's modulus, and Poisson's ratio. According to elastic constants calculations, KGaO3 are mechanically stable and ductile in nature. Further, refractive index, optical conductivity, the dielectric-constant, reflectivity, absorption coefficient, extinction coefficient, and loss function are calculated. According to the results, KGaO3 exhibits a high absorption in the visible region. This limits its application in photocatalytic water splitting characteristics.

Structural, dynamical and thermodynamical stability of Cd1-xZnxS ternary systems

Cd1-xZnxS alloys are currently explored as one class of the most promising for producing hydrogen energy under visible-light irradiation. Here, using an ab intio evolutionary algorithm, we reveal that CdS–ZnS systems can form nearly thermodynamically stable crystal phases of Cd3ZnS4 (P-43m), CdZnS2 (P-4m2), and CdZn3S4 (P-43m), with low miscibility temperatures of 130 °C. By decomposing the formation enthalpy of the alloys into multiple contributions, it is found that electronic charge exchange plays a key role in controlling the weak thermodynamic instability of Cd1-xZnxS alloys. Phonon dispersion and elastic constants calculations were carried out to demonstrate the dynamical and mechanical stabilities of these structures. The bandgap in CdZnS alloys is tunable from wide direct bandgaps of 2.54eV (CdS) → 2.70eV (Cd3ZnS4) →2.93eV (CdZnS2) → 3.33eV (CdZn3S4) → 3.86eV (ZnS), with a nonlinear dependence on the composition. We found a medium-sized optical bandgap bowing of ∼1eV and ∼0.7eV; while considering respectively the wurtzite (WZ) and zinc-blend (ZB) crystal phases as reference of the compounds parents CdS and ZnS. The bowing has a remarkable contribution due to the structural volume-deformation effect; whereas charge exchange contribution is found relatively weak.

Large perpendicular magnetic anisotropy, high curie temperature, and half-metallicity in monolayer CrSI induced by substitution doping

The experimental discovery of two-dimensional (2D) intrinsic ferromagnets have sparked intense interest due to their potential applications in spintronics. However, the small magnetic anisotropy and low Curie temperature (TC) hinder their applications. Herein, through comprehensive first-principles calculations and Monte Carlo simulations, we investigate how Mn substitution doping affects the structure, electronic structure, magnetic properties, and TC of monolayer CrSI. Our calculations show that in contrast to ferromagnetic semiconductor with a TC of 175 K of monolayer CrSI, Mn doped monolayer CrMnS2I2 is a half-metallic ferromagnet with a TC of 312 K. Different from in-plane magnetic anisotropy of monolayer CrSI, the easy axis of monolayer CrMnS2I2 is out-of-plane, and the magnetic anisotropy of monolayer CrMnS2I2 can reach to 1.434 meV/atom, which is much larger than 0.001 meV/atom of monolayer CrSI. Additionally, the phonon dispersion, ab initio molecular dynamics simulations, formation energy, and elastic constants calculations indicate that monolayer CrMnS2I2 possesses excellent stability. Our findings provide a promising route to realize 2D intrinsic ferromagnetic half-metallic materials with a high TC and a large perpendicular magnetic anisotropy.

Elastic constants of nano-scale hydrated cement paste composites using reactive molecular dynamics simulations to homogenization of hardened cement paste mechanical properties

Calcium-silicate-hydrates, portlandite and ettringite are the main hydrated cement paste phases. The study of these phases might lead to a better understanding of the mechanical properties of hardened cement paste. In this work, molecular dynamics simulations were used to simulate different composites of these main phases. The objective were to obtain their elastic constants and to use them as a reference to calculate the homogenization of simplified hardened cement paste using Mori-Tanaka scheme. The results of calcium-silicate-hydrate/calcium-silicate-hydrate, calcium-silicate-hydrate/portlandite and calcium-silicate-hydrate/ettringite composites with three different orientations and configurations were obtained via molecular dynamics simulations using a software called LAMMPS. The homogenization of simplified hardened Portland cement paste gave the value of Young’s modulus in the range from 10.1 GPa to 15.1 GPa. This method might be able to determine Young’s modulus of normal hardened cement paste by the calculations of elastic constants of different composites with other hydrated and unhydrated phases.

Structural and mechanical properties of NiTiAg shape memory alloys: ab-initio study

The austenite phase of Ni50−x Ti50Ag x for different concentrations (x = 1, 1.5, 2, 3, 5, 7, 8, 10) has been analyzed in this work. The ground state, structural, and mechanical characteristics of Ni50−x Ti50Ag x for various concentrations are examined under ambient conditions. From total energy as well as formation energy calculations, it is found that the stability of Ni50−x Ti50Ag x austenite phase is increased up to x = 5 and after that it becomes unstable in nature. These results are in good agreement with our experimental results. The experimental and other theoretical results agree with the estimated lattice parameter values. The x-ray diffraction and differential scanning calorimetry reveal the phases formed and transformation characteristics of NiTiAg alloys. The elastic constants, bulk modulus, shear modulus, Poisson’s ratio, and elastic anisotropy factor of Ni50−x Ti50Ag x are examined at ambient conditions for different concentrations. From elastic constant calculations, it is also found that the austenite phase of Ni50−x Ti50Ag x is mechanically stable up to x = 5 and after that it does not obey Born–Huang criteria and becomes unstable. The Ni45Ti50Ag5 composition is found to be the stiffest and hardest material. According to Poisson’s ratio calculations, Ni50−x Ti50Ag x shows that the Ti–Ag, Ni–Ag bonding is more directed in nature. The austenite phase of Ni50−x Ti50Ag x is more incompressible because the Poisson’s ratio is nearly equal to the optimum value (0.5).

SCAPS simulation and DFT study of lead-free perovskite solar cells based on CsGeI3

With the rapid development of perovskite solar cells (PSCs), environmentally friendly germanium-based PSCs have begun to appear in people's vision. We have designed a perovskite solar cell structure consisting of FTO/Cd0.5Zn0.5S/CsGeI3/MoO3/Au. Our study focused on analyzing the impact of various factors such as the absorption layer, electron transport layer (ETL), hole transport layer (HTL), interfacial defect layer (IDL), and temperature, on device performance. We optimized various parameters of the device, and as a result, the final PCE reached an impressive 35.91%. In addition, we conducted an analysis of the perovskite absorber layer using density functional theory (DFT) and investigated the function of Ge atoms in the perovskite absorber layer. The results show that, for HTL, altering the doping concentration of the ETL has a more significant impact on PSCs. When the operating temperature exceeds 300K, only the short-circuit current (Jsc) increases. When the defect density exceeds 1013cm−3, the rate of carrier recombination begins to increase significantly, along with the interface defect layer. We also analyzed the energy band, density of states, charge density difference, charge population, and elastic constants of the absorption layer using density functional theory (DFT). The results indicate that Ge atoms play a crucial role in photon absorption and photocurrent generation, which is a significant factor contributing to the high power conversion efficiency of germanium-based PSCs. Due to the transfer of electric charge from the Ge atom to the periphery of the I atom and the hybridization between the Ge-4p and I-5p orbitals, the Ge–I bond is formed and stabilized. Finally, the calculation of elastic constants shows that CsGeI3 is a stable mechanical structure.

Transforming III-V binaries into stable ternary materials for solar cells applications

The world speedily growing energy demand motivates vivid interest and intensive searching new optimal direct bandgap materials for efficient thin-film photovoltaic cell devices. Here, we present solar cell materials search using density functional theory and ab initio evolutionary algorithm. The compounds in focus belong to cationic ternary III-V family. It is found that AlGaN2 (P3m1), InGaN2 (P3m1), AlGaP2 (P4‾ m2) InGaP2 (R3m), AlGaAs2 (R3m) and InGaAs2 (R3m and P4‾ m2) are weakly unstable (enthalpy of formation between 4 and 76 meV) with respect to decomposition, the vibrational calculations divulge that these materials should be synthesized under moderate growth temperature. Moreover, phonon dispersion and elastic constants calculations evince dynamical and structural stability of these compounds.Accurate electronic band structures evidence that most of the ternary III-V materials are semiconductors with direct bandgaps except AlGaP2 that is found indirect. Based on the metric of spectroscopic limited maximum efficiency, solar cell efficiency of AlGaAs2, InGaAs2 (R3m), InGaP2, InGaN2, and InGaAs2 (P4‾ m2) is predicted respectively to be 24%, 24.6%, 25.9%, ∼30% and ∼30.6%, which exceeds those of materials currently used as absorber layer.

Scrutinized the spin-orbit coupling effect on the elastically and thermodynamically stable Rb2BCl6 (B = Pb, Ti) double perovskites for photocatalytic, optoelectronic and renewable energy applications

In this report, the electronic structure, mechanical stability, optoelectronic, thermoelectric and photocatalytic response of inorganic halide perovskites Rb2BCl6 (B= Pb, Ti) have been simulated first time by using density functional theory (DFT). Modified Becke-Johnson (mBJ) potential along with spin-orbit coupling (SOC) effect is applied for accurate calculations. The calculated ground-state lattice parameters, negative formation energy values and positive phonon frequencies endorse the stability of both compounds. The band structure plots display the semiconductor character of both perovskites. The mechanical stability has been determined with the Bulk and Young modulus, Poisson ratio, along with the calculation of elastic constants. The calculated optical response reveals a high dielectric constant and absorption coefficient with low reflectivity. These compounds are revealed to have a higher figure of merit (ZT) than the typical metal halide perovskites with the values of 0.732 and 0.72 for Rb2PbCl6 and 0.724 and 0.71 for Rb2TiCl6 at 800K with mBJ and mBJ+SOC, respectively. The Seebeck coefficient and figure of merit present good values at high temperatures. The photocatalytic activity has shown the water-splitting ability of Rb2TiCl6. The overall analysis of the calculated properties shows that the studied halide perovskites are suitable for optoelectronic, thermoelectric and photocatalytic applications.

The SCF convergence criteria of the ab initio calculations of elastic properties of single-crystal B2 ZrPd phase

The mechanical and dynamical stability of the geometry optimised structural phases of Zr50Pd50-xRux have been calculated using the ab initio modelling technique. The accuracy of the elastic constants largely depends on the accuracy of the self consistent field (SCF) setting and also on the level of convergence of geometry optimisation for each distorted structure. Parameters such as energy cutoff, SCF convergence criteria and k-points set form part of these calculations. Often, the importance of setting accuracy of these parameters is neglected and may result in erroneous reporting of elastic constants. In the present study, B2 ZrPd is used to demonstrate the disadvantage of inaccurate selection of energy cutoff and k-points set on the calculation of elastic constants. The computed results of phonon dispersion curves were in excellent agreement with existing experimental data, and further aided in resolving discrepancy among theoretical results. While current results showed that the B2 phase of ZrPd is neither mechanically or vibrationally stable at 0 K, contrary to some of the previous calculations, the phonon dispersion curves of all considered ZrPd phases reveal presence of imaginary frequencies. Introduction of Ru on Pd site of the B2 ZrPd has negligible effect on the thermodynamic stability (Hf), but increased both mechanical and lattice dynamic stability significantly. In addition, it is predicted for the first time from lattice dynamic calculations that addition of 18.75 at.% Ru alters the martenstic transformation path from that of pristine ZrPd towards that of TiNi. Lattice vibration results for other chosen reference alloys are also in excellent agreement with existing theoretical data.