Equilibrium Lattice Parameters Research Articles

Structural, electronic, optical, mechanical, and phononic bulk properties of tetragonal trirutile antimonate MSb2O6 (M = Fe, Co, Ni, or Zn): a first-principles prediction for optoelectronic applications

Abstract This work does an extensive analysis of the optoelectronic and mechanical properties of the tri rutile structure type 3d transition metal Antimonate MSb2O6 (M = Fe, Co, Ni, or Zn), for the first time, utilizing the pseudo-potential plane wave approach within the density functional theory framework. When calculating the structural, optical, and mechanical properties, the exchange–correlation interactions were studied using the GGA-PBE functional, whereas when computing electronic, it is analyzed using the HSE06 hybrid functional. The equilibrium lattice parameters exhibit good agreement with the available experimental results. The electronic properties were estimated using the GGA-PBE and HSE06 functionals. Based on the calculated electronic properties with the GGA-PBE functional, the FeSb2O6, CoSb2O6, and NiSb2O6 materials exhibit metallic behavior with energy gap values of 0 eV, while ZnSb2O6 is a semiconductor with a narrow direct band gap (Γ–Γ) of 0.5 eV. Furthermore, the computed band gaps using the HSE06 functional are 0 eV, 0 eV, 1 eV (Γ–Γ), and 4 eV (Γ–Γ) for FeSb2O6, CoSb2O6, NiSb2O6, and ZnSb2O6, respectively. Density of states diagrams were used to gain deeper insights into the characteristics of the energy bands. The optical properties of these compounds, such as the dielectric function, energy loss function, conductivity, reflectivity, refractive index, and absorption coefficient were investigated over the energy range of 0 to 40 eV. The materials exhibited a high absorption coefficient and a significantly low reflectivity within the UV–vis energy spectrum. The negative cohesive energy Ecoh implies the chemical (thermodynamic) stability of the trirutile MSb2O6 (M = Fe, Co, Ni, or Zn). Mechanical stability is confirmed by applying the Born stability criteria using elastic constants (Cij). The absence of imaginary frequencies in the phonon spectrum calculations confirms the dynamic stability of the studied compounds. These results are consistent with previous experimental research on these materials in photocatalysis and gas sensor applications. On the other hand, these compounds possess exceptional high and broad optical absorption UV range, making them suitable for use in next-generation ultraviolet photodetectors.

Novel Tl2SnX6 (X=Cl,Br) Double Perovskites for Photovoltaic Applications: A DFT Insight

New double perovskites Tl2SnCl6 and Tl2SnBr6 have been computationally investigated for the first time to determine their structural, mechanical, and optoelectronic properties. The calculations were carried out using Density Functional Theory (DFT), implemented in the Quantum Espresso and Thermo_pw codes. DFT is a theoretical framework used to accurately predict the ground state properties of quantum many-body systems ranging from atoms to condensed matter systems. The results indicated that Tl2SnCl6 and Tl2SnBr6 possess equilibrium lattice parameters of 10.28 Å and 10.77 Å, respectively. Their negative formation energy ensures chemical stability while their positive elastic tensors imply mechanical stability, which is also confirmed by the fulfillment of the Born-Huang stability criteria. Analysis of their Poisson’s and Pugh’s ratio suggested that the materials are brittle but Tl2SnCl6 was estimated to be ductile in some directions. The materials were found to possess semiconducting behavior with bandgap of 1.19 eV (1.48 eV) and 2.48 eV (2.84 eV) for Tl2SnBr6 and Tl2SnCl6, respectively, using the PBE (SCAN) functionals. The calculated optical characteristics indicated that both Tl2SnCl6 and Tl2SnBr6 exhibit remarkable optical properties including significantly high absorption coefficient and low reflectivity, rendering their potential as light absorbers. In particular, with an ideal band gap of 1.48 eV and strong absorption in the visible region of the solar spectra, Tl2SnBr6 is predicted to be an excellent absorber for perovskite solar cells.

First-principles calculations to investigate phase stability, elastic and thermodynamic properties of TiMoNbX (X=Cr, Ta, Cr and Ta) refractory high entropy alloys

This work uses first-principles calculations to investigate the phase stability, thermophysical and mechanical properties of refractory high entropy alloys (RHEAs) at finite temperatures. On the basis of plane wave quasi-potential and density functional theory, construct the structure model of a solid solution. The TiMoNbX (X = Cr, Ta, Cr and Ta) RHEAs have been determined to preserve a single body-centered cubic solid solution structure by calculations and the equilibrium lattice parameters and elastic modulus are consistent with experimental data obtained by laser cladding, which is combined with TC4 (Ti-6Al-4V) substrate. Using the quasi-harmonic Debye-Grüneisen model, the thermophysical characteristics of three RHEAs are investigated. The Voigt-Reuss-Hill scheme is used for calculating the Young's modulus (E), bulk modulus (B), shear modulus (G), and Poisson's ratio (ν), which indicates that all three RHEAs are ductile materials. Additionally, the modulus and hardness of materials decrease as temperature rises, whereas the properties of TiMoNbX RHEAs are predicted, as the nanoindentation hardness values at room temperature are comparable to, and slightly higher than the calculated values.

First Principle Study of Structural, Electronic, Mechanical and Optical Properties of Bulk Niobium Dichalcogenide NbX2 (X=S, SE) within a Visible Phonon Energy Range

An intensive study on structural, electronic mechanical and optical properties of bulk Niobium Dichalcogenides NbX2 (X=S, Se) was carried out using the first principle. The structural parameters such as Equilibrium Lattice Parameters, Volume, Bulk Modulus, and FirstDerivative Modulus were calculated to determine if the materials are energetically stable. Elastic constants were further obtained from which mechanical properties i.e. bulk, Young's and shear moduli and consequently Poisson's ratio were obtained. Based on the well-known Born stability conditions Bulk-NbS2 is most likely mechanically anisotropic ductile material. While Bulk-NbSe2 for the predicted B/G ratio in all three methods is less than a critical value of 1.75, hence this shows that NbSe2 is a brittle material exploring its electronic and optical properties whose motivation was to find out the most stable phase and ascertain if these materials could be used in various fields that suit their mechanical and optical properties. Furthermore, from the calculated optical spectra, plasma frequencies were analyzed which indicated the possibility of applying the material in plasmonic-related fields.

Fitting to magnetic forces improves the reliability of magnetic Moment Tensor Potentials

We developed a method for fitting machine-learning interatomic potentials with magnetic degrees of freedom, namely, magnetic Moment Tensor Potentials (mMTP). The main feature of our method consists in fitting mMTP to magnetic forces (negative derivatives of energies with respect to magnetic moments) as obtained spin-polarized density functional theory calculations. We test our method on the bcc Fe–Al system with different compositions. Specifically, we calculate formation energies, equilibrium lattice parameter, and total cell magnetization. Our findings demonstrate an accurate correspondence between the values calculated with mMTP and those obtained by DFT at zero temperature. Additionally, using molecular dynamics, we estimate the finite-temperature lattice parameter and capture the cell expansion as was previously revealed in experiment. Furthermore, we demonstrate that fitting to magnetic forces increases the reliability of structure relaxation (or, equilibration), in the sense of ensuring that every relaxation run ends up with a successfully relaxed structure (the failure may otherwise be caused by falsely driving a configuration away from the region covered in the training set).

DFT insight into the phase stability, optoelectronic, elastic, vibrational, and thermodynamic properties of metal chalcogenides RbKM (M = S, Se, Te) for energy harvesting technology

In this manuscript, the structural, optoelectronic, elastic, vibrational, and thermodynamic properties of RbKM (M = S, Se, Te) chalcogenides are explored via first principles approach. The estimated equilibrium lattice parameters a(c) through the TB-mBJ functional are 5.3876 Å (8.2810 Å), 5.2700 Å (8.6550 Å) and 5.2656 Å (8.7707 Å) for RbKS, RbKSe and RbKTe, respectively. The large value of the cohesive (Ecoh) and formation energy (Eform) reveals that all these compounds are stable at 0 K that may be difficult to decompose at ambient conditions. The direct band gap for RbKS, RbKSe and RbKTe is noted as 4.05 eV, 3.71 eV and 3.63 eV, respectively that is sufficient to declare them as semiconducting materials. So far as, the projected density of states (PDOS), pseudo electrons residing in d orbitals of the rubidium atoms contribute in the conduction region and p orbitals of chalcogen elements partake in the valence band. The optical parameters are determined by Kramers-Kronig relations. The elastic constants unveil that all compounds are mechanically stable and hold anisotropic nature. Here the vibrational properties of RbKM (M = S, Se, Te) are examined through Density functional perturbation theory (DFPT) technique. The Harmonic Approximation Method (HAM) is utilized to seek thermodynamic stability that is ensured due to the observance of negative free energy for all cases. Our theoretical outcomes for RbKM (M = S, Se, Te) can contribute significantly to amelioration for future research in devising optoelectronic and energy harvesting like appliances.

FP-LMTO simulation of the physical properties of arsenic-based binary XAs(X = Sc, and Al) compounds

This paper presents a simulation of the structural and optoelectronic properties of Scandium Arsenide (ScAs) and Aluminum Arsenide (AlAs) compounds. Theoretical modeling was performed using ab initio first-principles calculations, specifically the density functional theory (DFT), and the Mindlab numerical software. The software used two methods: the full-potential muffin-tin orbital method (FP-LMTO) and the full-potential plane-wave method (FP-LAPW). These two methods are employed to solve the Schrödinger equation. The exchange correlation effects have been computed using two different approximations: the generalized gradient approximation (GGA) and the local density approximation (LDA). Our findings indicate that the zinc blende structure (B3) is the stable phase, while the Wurtzite phase (B4) is metastable for the AlAs compound. On the other hand, the ScAs compound crystallizes in the NaCl phase (B1). The AlAs compounds undergo three phase transitions: [Formula: see text], [Formula: see text] and [Formula: see text]. In contrast, ScAs does not undergo any transition. The obtained results for equilibrium energies, lattice parameters and gap energies are in closer agreement with the experimental and theoretical data. The AlAs compound exhibits a semiconducting character, while ScAs exhibits a semi-metallic character. Additionally, the refractive index of these two compounds is similar to that of silicon, which is crucial for their application in photovoltaic cells.

Computational Investigation of Structural, Electronic and Optical Properties of Ternary Chalcogenide TLGaQ2 Monoclinic Compounds: a First Principle Study

Purpose: This paper aim to investigate and predict by simulation the impact of the substitution of Q-site atom (Q꞊S, Se) on the TIGaQ2 monoclinic compounds for the first time, along the three main polarizations of the incident wave directions [100], [010] and [001]. Theoretical Framework: This study focuses mainly on ternary chalcogenide compounds TlGaQ2 (Q= S, Se) from ABQ2 family to highlight the objective resources aimed at promising prospects offered for them. Design/Methodology/Approach: A series of ab-initio calculations based on the (PW+PP) method within the density functional theory DFT framework were carried out with CASTEP code for the simulation of their physical properties (structural, electronic-optical). The exchange correlation potential was treated within the generalized gradient approximation (GGA) implemented in the CASTEP code and expressed by the PBE functional. Findings: The equilibrium lattice parameters are in good agreement with the available experimental results. The calculated band structure shows that are direct bandgap semiconductor nature 1.92eV (1.41eV) for TlGaS2 and TlGaSe2 respectively with a great potential for photovoltaic solar cell absorber materials. A set of optical parameters were calculated including the complex dielectric function, the reflective index, reflectivity, the absorption coefficient and loss function. The optical properties obtained revealed very interesting optical properties exhibiting strong optical absorption in UV range up to (~2x105cm-1) for both compounds making them appropriate for photovoltaic solar-cell absorber materials. Furthermore, low reflectivity and energy loss function are shown within in the visible and ultraviolet energy range, allowing them to be promising materials in several optoelectronics applications likes photosensitive devices. Implications: All these findings results show a successful accurately prediction for chalcogenide materials behavior and will be helpful for future studies allowing a better understanding of their potential applications in modern photovoltaic technologies as well as within UV ranges for optoelectronics applications.

Exploring novel filled skutterudites: A comprehensive DFT Modeling study on electronic, magnetic, curie temperature, elastic, thermal, and thermoelectric properties

Embarking on a captivating journey through the intricacies of two groundbreaking Skutterudite compounds, BaMn4X12 (X = As, Sb), employing first-principles calculations based on the Generalized Gradient Approximation (GGA) and modified Beck-Johnson approximation (mBJ) of density functional theory (DFT), has unveiled intriguing revelations. These compounds showcase exceptional stability within the ferromagnetic phase of the BaMn4As12 and BaMn4Sb12 cubic-type structure, boasting equilibrium lattice parameters of 0.933 nm for BaMn4As12 and 0.92 nm for BaMn4Sb12. The electronic properties point to their half-metallic nature, and a thorough analysis of elastic properties confirms their remarkable stability, high rigidity, anisotropy, and minimal deformation, exhibiting a ductile behavior. The magnetic properties analysis underscores the ferromagnetic state of both compounds, revealing a computed total magnetic moment of 4.76 μB for BaMn4As12 and 4.60 μB for BaMn4Sb12. Finally, our examination of the thermodynamic parameters of these compounds, conducted across temperatures ranging from 0 to 800 K and pressures from 0 to 40 GPa using the quasi-harmonic Debye model, underscores their immense potential for diverse applications. These findings inspire excitement, showcasing the promising avenues for the utilization of BaMn4X12 (X = As, Sb) compounds in various fields, including materials science, engineering, and technology. Additionally, the fundamental application of semi-classical Boltzmann theory has been incorporated into the advanced framework of BoltzTraP to investigate its transport coefficients. Hence, the general inclination of these specific compounds may support their potential for various applications in sustainable thermoelectrics, spintronics features, and more.

Theoretical Investigation of The Properties of LiRuAs Semi-Heusler Alloy via Density Function Theory

The structural, thermal, electronic and elastic properties of LiRuAS semi Heusler alloy were investigated using a generalized gradient approximation (GGA) approach, which employs a density functional theory (DFT) to examine the alloy's optimized equilibrium lattice parameter. The optimized lattice parameter was found to be 5.601 Å. The results of the calculations indicate that the alloy exhibits mechanical stability, flexibility, non-magnetic conductivity, malleability, compressibility, and anisotropy.

Investigating structural, phonons, optoelectronics, and thermodynamic properties of lead-free double perovskites of A-site cation ordering in LiXTl2Cl6 (X= Sc and Y) compounds for green energy applications

This study explores the structural, phonons, optoelectronic, and thermodynamic properties of LiXTl2Cl6 (X = Sc and Y) compounds. These double perovskite materials are particularly interesting due to their potential for green energy applications. We employ state-of-the-art computational simulation techniques to investigate the structural properties of these compounds, focusing on the cation ordering in the A-site of the perovskite structure. Through density functional theory (DFT) calculations, we determine the equilibrium crystal structure and lattice parameters, shedding light on the stability of these materials. Furthermore, we analyze the phonon spectra to assess the materials' vibrational properties, including the presence of any phonon modes that may impact thermal stability and thermal transport. Optoelectronic properties, such as band gaps and optical absorption spectra, are also explored to evaluate the suitability of these materials for photovoltaic and light-emitting applications. We investigate their electronic structure and consider the potential for efficient charge carrier generation and transport. The thermodynamic properties, such as heat capacity, entropy, and enthalpy, are calculated to provide insight into the compounds' thermal behavior under various environmental conditions, which is crucial for green energy applications, including thermal energy conversion. This comprehensive investigation into the LiXTl2Cl6 (X = Sc and Y) compounds aims to contribute to developing lead-free double perovskite materials with tailored properties for a range of green energy applications, paving the way for more sustainable and environmentally friendly energy solutions.

Computational investigation of the structural, elastic, electronic, and thermodynamic properties of chloroperovskites GaXCl3 (X = Be, Ca, or Sr) using DFT framework

In this study, we employed the pseudopotential plane wave approach to examine the influence of the X atom (X = Be, Ca, or Sr) on the physical properties of isostructural chloroperovskites GaXCl3. The GGA-PBEsol functional was employed to simulate the exchange–correlation interactions. The computed equilibrium lattice parameters exhibit a high level of concordance with the existing theoretical findings. The cohesion energy and enthalpy of formation were computed to verify the energetic stability of the materials under consideration. The determined values of the single-crystal elastic constants (Cij) indicate that GaBeCl3 remains mechanically stable up to a hydrostatic pressure of 18 GPa. Similarly, GaCaCl3 preserves its stability up to 5 GPa, while GaSrCl3 remains mechanically stable up to 1.25 GPa. The projected Cij values were used to estimate several elastic moduli and related properties, including the shear and bulk moduli, sound wave speeds, Young’s modulus, Poisson’s ratio, and Debye temperature. The energy band structures of the studied compounds, as predicted by the HSE06 functional, demonstrate their wide bandgap semiconductor nature. Specifically, GaBeCl3 demonstrates an indirect bandgap of 3.828 eV, while GaCaCl3 reveals an indirect bandgap of 4.612 eV and GaSrCl3 has an indirect bandgap of 4.405 eV. The quasiharmonic Debye approach was employed to examine various thermal parameters, including the temperature dependence of the unit cell volume, bulk modulus, expansion coefficient, Debye temperature, isochoric and isobar heat capacities, Grüneisen parameter, and entropy function. It has been shown that GaBeCl3 demonstrates a lower thermal expansion coefficient and a higher Debye temperature in comparison to GaCaCl3 and GaSrCl3.

Ab initio predictions of pressure-dependent structural, elastic, and thermodynamic properties of GaMF3 (M = Ca, and Sr) halide perovskites

The structural, elastic, and thermodynamic characteristics of the GaCaF3 and GaSrF3 halide perovskites have been predicted for the first time, using ab initio pseudopotential plane wave calculations. The equilibrium lattice parameters are in good agreement with previously documented results. Both compounds exhibit substantial thermodynamic and mechanical stability. The single-crystal and polycrystalline elastic properties and related properties have been examined. GaCaF3 exhibits higher hardness than GaSrF3. The temperature dependence of the lattice parameter, bulk modulus, volume thermal expansion coefficient, heat capacity, and Debye temperature, have been computed using ab initio calculations combined with the quasi-harmonic Debye model.

Investigating the electronic structure, elastic, magnetic, and thermoelectric nature of NiV X Sc1−X Sb quaternary half-Heusler alloys

The structural, electronic, magnetic, elastic, and thermoelectric properties of NiV x Sc1−x Sb half Heusler alloys with different compositions were investigated employing a self-consistent first-principles-based calculation that uses the full-potential linearized-augmented-plane-wave method. The structural characteristics, such as the bulk modulus and lattice constants, are examined with various vanadium concentrations. The accurately modified Becke Johnson potential was used to calculate the band gap energies. The equilibrium lattice parameter of the NiScSb type-I structure has the lowest energy and seems to be most stable among the other configurations, with a lattice constant value of 6.04 Å, which deviates from the experimental results by up to 0.5%. The bulk modulus rises as the lattice constant decreases. The ground states of the studied alloy structures are dynamically stable, as concluded by the non-existence of negative phonon frequencies. The band structure of NiScSb (for x = 0) was predicted as a non-magnetic semiconductor with an indirect band nature and an energy gap value of 0.244 eV along (Γ-point > X). This tendency was further supported by the symmetrical shape of the curves that reflect the densities of states for these configuration channels. The thermoelectric characteristics of these various combinations were also thoroughly investigated and discussed.

Computational study on the structural, electronic, lattice vibration, and magnetism in Zn(1−x)FexSeyTe(1−y) quaternary materials

In this article, we studied the structural, electrical, lattice vibrational, and magnetic properties of the quaternary compound Zn(1−x)FexSeyTe(1−y) using density functional theory. All the calculations have been performed based on first-principles calculations using Perdew–Zunger [local-density approximation (LDA)] and Hubbard parameter correction (LDA+U) functionals as employed in the Quantum Espresso package. The computed equilibrium lattice parameter for ZnTe is 6.01 Å, and the energy bandgap, Eg, is 1.362 eV, which is consistent with the experimental values as well as the previous reports, respectively. The influence of the co-doping of iron and selenium on electrical and magnetic properties in a ZnTe system is discussed in detail. The co-doping of iron and selenium affects metallic behavior in these systems by forming localized states between the conduction and valance bands. The presence of localized states is related to the metallic properties of the iron atom, specifically iron 3d orbitals. The spin-polarized density of state and band structure computations also confirmed that the iron and selenium co-doped ZnTe system exhibits significant half-metal ferromagnetic and dilute magnetic semiconductor features at room temperature. Furthermore, the phonon calculation of these systems indicated that the systems are dynamically stable and that localized frequency states are created at higher frequencies due to the presence of iron atoms. As a result, the iron and selenium co-doped ZnTe systems can be considered for magnetic and spintronic device applications at room temperature, pending further experimental research.

Theoretical investigation of structural instabilities of newly predicted superconducting Heusler alloys Rh2NbZ (Z = Al, Ga, Sn): Ab initio approach

We systematically investigate the structural and elastic properties of Rh2NbZ (Z = Al, Ga, Sn) through ab initio calculations. We determine the equilibrium lattice parameters in the cubic austenitic phase of Rh2NbZ and observe martensitic structural transitions in all compositions. These transitions are attributed to the lone pair effect of s electrons on the Z element, leading to a paramagnetic ground state for all alloys. In addition, we discover superconducting behavior of Rh2NbZ, as evident from the total density of states plots. Furthermore, we calculate various elastic parameters in cubic phase to understand the structural stability.

(Digital Presentation) Designing New Complex Hydrides Based on Transition Metals for Hydrogen Storage Applications

The widespread implementation of the hydrogen economy demands access to materials with a high weight percentage of hydrogen. Mg-based hydrogen storage alloys have become a research hot-spot in recent years owing to their high hydrogen storage capacity, good reversibility of hydrogen absorption/desorption, low cost, and abundant resources. However, high decomposition temperature of Mg-based hydrideslimits their practical usage. Hydrogen is lightest of all elements, typically it need large volumes or high pressures to store appreciable amount of hydrogen.To overcome these challenges research activities are currently going on metal hydrides and complex hydrides based on transition metal. The main challenges come when endothermic decomposition enthalpy is considered. It becomes difficult to release the hydrogen at ambient thermodynamic conditions. On the other hand, the meta-stable hydrides are characterized by a low reaction enthalpy and a decomposition reaction that is thermodynamically favourable under the ambient conditions. The good kinetics along with evolution of hydrogen around the room temperature possessed by these materials offer much promise for underground storage and it can be used as a grid energy.The present research specifically focus on transition metal based complex hydrides such as NaMgMnH6 and NaMgFeH6 for hydrogen storage and especially predicted the crystal structure of the same using VASP simulation package. ABCX6 and AB2X6 were taken as reference composition A,B,C and X were substituted with Na, Mg, transition metals(Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu) and H, respectively.From the ICSD database search the corresponding structural variants were considered as trial structure to predict the ground state structure of these newly designed compounds. using the predicted ground state structure for these compounds, important properties like formation energy, hydrogen site energy, partial density of states(pDOS), electron density(ED), Mulliken effective charge(MEC), Bader electron charge(BEC), Born effective charge, ELF and COHP were calculated. the calculated properties of these compounds were compared with the well known reference compounds. We found that both NaMgMnH6 and NaMgFeH6 are stable with negative formation energy and als othey are semiconductors with the band gap value of 0.51eV and 1.01 eV, respectively. from the calculated electronic structure we found that both these materials are having indirect band behaviour. Analysing the electronic density of states, charge density and various charges mentioned above the chemical bonding behaviour was established as iono-covalent in nature. from the force as well as stress minimisation considering 53 structural variants as input the ground state structure, its space group, equilibrium lattice parameters and atom positions are listed. Also from the energy vs. volume curve for the ground state structure, the equilibrium volume, bulk modulus and pressure derivatives were found out. Among NaMgMnH6 and NaMgFeH6 our spin polarised calculation show that NaMgMnH6 is possesing spontaneous magnetic polarisation with substantial magnetic moment at the Mn site. Among the considered paramagnetic, ferromagnetic, as well as A-, C-,and G- antiferromagnetic configurations the G type antiferromagnetic configuration is found to be the ground state for NaMgMnH6.

New insight into the structural, elastic, dynamics and thermodynamic properties of Fe3P under high pressures

Many efforts have been devoted to developing the linkage between atomic characteristics and the mechanical properties. Equilibrium lattice parameters, elastic constants, dynamics and thermodynamic properties of Fe3P are systematically explored by density functional theory (DFT) calculations with a generalized gradient approximation (GGA) from Perdew-Wang's 1991 (GGA-PW91), Perdew-Burke- Erzenhof (GGA-PBE), local density approximation (LDA), GGA-PW91+U, GGA-PBE + U and (LDA) + U method (U is the Hubbard correction), respectively. It concluded that the lattice parameters and bulk modulus B from GGA-PBE + U results tend to be more compatible with experimental results than others. The elastic moduli of Fe3P is reported based on the Voigt-Reuss-Hill model. Meanwhile, the anisotropy index and the three dimensional (3D) surface profile of Young's modulus determine the anisotropy. The obtained results indicate that Fe3P exhibits strong elastic anisotropy under high pressure. In addition, the dynamical and mechanical stabilities of Fe3P are confirmed by calculating the phonon and elastic constants up to 40 GPa. Finally, we studied the thermodynamic properties of Fe3P under pressures based on quasi-harmonic approximation.

TurboGenius: Python suite for high-throughput calculations of ab initio quantum Monte Carlo methods

TurboGenius is an open-source Python package designed to fully control ab initio quantum Monte Carlo (QMC) jobs using a Python script, which allows one to perform high-throughput calculations combined with TurboRVB [Nakano et al. J. Phys. Chem. 152, 204121 (2020)]. This paper provides an overview of the TurboGenius package and showcases several results obtained in a high-throughput mode. For the purpose of performing high-throughput calculations with TurboGenius, we implemented another open-source Python package, TurboWorkflows, that enables one to construct simple workflows using TurboGenius. We demonstrate its effectiveness by performing (1) validations of density functional theory (DFT) and QMC drivers as implemented in the TurboRVB package and (2) benchmarks of Diffusion Monte Carlo (DMC) calculations for several datasets. For (1), we checked inter-package consistencies between TurboRVB and other established quantum chemistry packages. By doing so, we confirmed that DFT energies obtained by PySCF are consistent with those obtained by TurboRVB within the local density approximation (LDA) and that Hartree–Fock (HF) energies obtained by PySCF and Quantum Package are consistent with variational Monte Carlo energies obtained by TurboRVB with the HF wavefunctions. These validation tests constitute a further reliability check of the TurboRVB package. For (2), we benchmarked the atomization energies of the Gaussian-2 set, the binding energies of the S22, A24, and SCAI sets, and the equilibrium lattice parameters of 12 cubic crystals using DMC calculations. We found that, for all compounds analyzed here, the DMC calculations with the LDA nodal surface give satisfactory results, i.e., consistent either with high-level computational or with experimental reference values.

Constrained DFT-based magnetic machine-learning potentials for magnetic alloys: a case study of Fe–Al

We propose a machine-learning interatomic potential for multi-component magnetic materials. In this potential we consider magnetic moments as degrees of freedom (features) along with atomic positions, atomic types, and lattice vectors. We create a training set with constrained DFT (cDFT) that allows us to calculate energies of configurations with non-equilibrium (excited) magnetic moments and, thus, it is possible to construct the training set in a wide configuration space with great variety of non-equilibrium atomic positions, magnetic moments, and lattice vectors. Such a training set makes possible to fit reliable potentials that will allow us to predict properties of configurations in the excited states (including the ones with non-equilibrium magnetic moments). We verify the trained potentials on the system of bcc Fe–Al with different concentrations of Al and Fe and different ways Al and Fe atoms occupy the supercell sites. Here, we show that the formation energies, the equilibrium lattice parameters, and the total magnetic moments of the unit cell for different Fe–Al structures calculated with machine-learning potentials are in good correspondence with the ones obtained with DFT. We also demonstrate that the theoretical calculations conducted in this study qualitatively reproduce the experimentally-observed anomalous volume-composition dependence in the Fe–Al system.