ABINIT Code Research Articles

Theoretical investigation of electronic, mechanical, piezoelectric and thermodynamic properties of half-heusler LiBeAsxSb1-x alloys

This work is an investigation of the band structure and related properties of α-LiBeAsxSb1-x half-Heusler alloys. The computations were performed with the help of density functional theory, using the alchemical mixing approximation that ABINIT code offers. In addition, several thermodynamic quantities were examined and discussed. Our obtained results correspond to previous data. The investigated alloy system was found to be an indirect (Γ→X) semiconductor for all alloy contents x, ranging from zero to one. The current findings show that for an appropriate choice of alloy content and temperature, α-LiBeAsxSb1-x may provide other opportunities for advancing new physical properties that can be applicable to novel electronic devices.

Theoretical prediction by DFT on properties of β′-SrTa2O6 crystal

Based on the Density Functional Theory (DFT) electronic band structure, state density, linear optics, elastic, dynamic and thermodynamic properties of ??-SrTa2O6 crystal with P4/mbm (No. 127) space group were investigated with the help of ABINIT and Wien2k code. In the study, it was found that the ??-SrTa2O6 crystal is classified as a semiconductor with an indirect bandgap. For this crystal, the dielectric function was obtained and optical constants such as energy loss function, extinction coefficient, absorption coefficient and reflectivity were calculated. The components of the elastic stiffness tensor, the phonon dispersion, the state density and the contribution of each atom to the state density were obtained. Finally, thermodynamic properties were determined for the ??-SrTa2O6 crystal. Furthermore, the changes in free energy (F), internal energy (E), entropy (S) and heat capacity (C) depending on the temperature were investigated.

Structural and Theoretical Investigations on the Unique Coloring Scheme of the γ‐Brass Type Phase: Cu5+δCd8‐δ(−1.0≤δ≤0.1)

AbstractThe crystal structure of the γ‐brass type Cu5+δCd8‐δ(‐1.0≤δ≤0.1) in the Cu−Cd binary system has been analyzed by powder and single crystal X‐ray diffraction. All the compounds crystallize in the cubic space group(217). Mixing of Cu with Cd leads to a significant phase width. At the limiting composition, a previously unreported ordered compound Cu4Cd9is formed. The structure of all compounds is described by a 26‐atom γ‐cluster. Electronic structure calculations on the model structure built according to the ordered “Cu4Cd9”, show the presence of a pseudo‐gap at the Fermi level in the electronic density of states, which is consistent with other γ‐brass type phases. However, the site preference of Cu and Cd atoms is different from the other reported γ‐brass type structures in the Zn‐ and Cd‐rich phases. To address the “coloring problem”, a series of model structures were constructed with the composition Cu4Cd9and their total energies were compared with first‐principle calculations using ABINIT code. LOBSTER package was implemented to extract the bonding information by crystal orbital Hamilton population calculations.

Performance of the modified Becke–Johnson potential employing the pseudopotential plane-wave approach for band structure calculations

The modified Becke–Johnson exchange potential combined with local-density approximation correlation (mBJLDA) has recently attracted interest because it provides highly improved band gaps at a very low computational cost. In this work we performed an extensive investigation of the performance of the mBJLDA potential employing a norm-conserving pseudopotential plane-waves approach (mBJLDA@PP), as implemented in the abinit code, using a test set of 83 solids representing a wide range of semiconductors and insulators. Our results confirm the conclusion of our previous study that the number of electrons treated as valence in the pseudopotentials of the cations can have a significant impact on the calculated mBJLDA@PP band gaps. More specifically, while the use of typical pseudopotentials leads to accurate band gaps of certain systems, it yields significantly underestimated band gaps for other systems compared to experiment and to those of the all-electron mBJLDA (mBJLDA@AE) approach. The classes of the latter systems are identified, and this problem is resolved by including some outer core states as valence. The resulting mean absolute error in the calculated band gaps (compared to experiment) is of 0.46 eV, which is comparable to that of the mBJLDA@AE band gaps, reflecting the accuracy and reliability of the mBJLDA@PP approach for the band gap calculations.

An ab -Initio Study of Stability Dependence on Structure of Zinc oxide Nanowires .

The performed study has explored structural dependence of stability for different proposed shapes for Zinc Oxide nanowires by using pseudopotentials DFT calculations. 2-atom linear, 2-atom zigzag, 4-atom square and 6-atom hexagonal nanowire are the four different shapes under consideration and the study has been performed by using ABINIT code. Our findings indicate that 2 atom zigzag shaped nanowire has shown greatest stability

Extended first-principles molecular dynamics model for high temperature simulations in the Abinit code: Application to warm dense aluminum

The extended first-principles molecular dynamics (Extended FPMD) model introduced by Zhang et al. [2], based on an analytical single plane wave description of electronic orbitals for high energy electrons, has been implemented within the ab initio DFT software package Abinit and is now available. This model allows quantum simulations to be done smoothly on the full range of temperatures from cold condensed matter to hot dense plasmas passing through the warm dense matter regime which was currently not possible within the same ab initio model due to numerical limitations. In addition to presenting a brief theoretical background of the Zhang et al. method, we propose some improvements to the model. We then present the details of the implementation, and finally offer an application to the aluminum simulations for multiple densities, from room temperature to hot (thousands of eVs) temperature ranges, with a resulting Hugoniot equation of state that we compare with other methods.

Structural, electronic, magnetic and mechanical properties of three LaMnO3 phases: Theoretical investigations

First principles density functional theory is used to study the physical properties of LaMnO3 in its orthorhombic (Pnma), cubic (Pm-3m) and rhombohedral (R-3c) phases, using Full Potential Linearized Augmented Plane Wave (FP-LAPW) method implemented in the WIEN2k code. The exchange-correlation potential was treated with the WC-GGA + U approximation (where U is the Hubbard Coulomb energy term) for the calculation of the structural, electronic and magnetic properties, whereas the Tran-Blaha modified Beck-Johnson (TB-mBJ) potential is applied for the calculation of the electronic properties. We also used the ABINIT code to calculate mechanical properties. Our structural, electronic and magnetic calculations obtained are in good agreement with experimental ones. At equilibrium, spin polarization of the orthorhombic phase of LaMnO3 compound is antiferromagnetic (AFM) and we predict the ferromagnetic phase of the compound LaMnO3 to be half-metal with spin polarization of 100%. In addition, the bonding nature reveals a mixture of covalent and ionic bonding character. The ductility and brittleness are explored from mechanical properties, such as elastic constants, bulk modulus, shear modulus, Young's modulus, Poisson coefficient, B/G ratio and anisotropy ratio, and our obtained values indicate that LaMnO3 is a ductile and anisotropic material in the three phases. We have also investigated the elastic wave velocity and Debye temperature to collect more information on mechanical stability.

MechElastic: A Python library for analysis of mechanical and elastic properties of bulk and 2D materials

The MechElastic Python package evaluates the mechanical and elastic properties of bulk and 2D materials using the elastic coefficient matrix (Cij) obtained from any ab-initio density-functional theory (DFT) code. The current version of this package reads the output of VASP, ABINIT, and Quantum Espresso codes (but it can be easily generalized to any other DFT code) and performs the appropriate post-processing of elastic constants as per the requirement of the user. This program can also detect the input structure's crystal symmetry and test the mechanical stability of all crystal classes using the Born-Huang criteria. Various useful material-specific properties such as elastic moduli, longitudinal and transverse elastic wave velocities, Debye temperature, elastic anisotropy, 2D layer modulus, hardness, Pugh's ratio, Cauchy's pressure, Kleinman's parameter, and Lame's coefficients, can be estimated using this program. Another existing feature of this program is to employ the ELATE package (2016) [29] and plot the spatial variation of several elastic properties such as Poisson's ratio, linear compressibility, shear modulus, and Young's modulus in three dimensions. Further, the MechElastic package can plot the equation of state (EOS) curves for energy and pressure for a variety of EOS models such as Murnaghan, Birch, Birch-Murnaghan, and Vinet, by reading the inputted energy/pressure versus volume data obtained via numerical calculations or experiments. This package is particularly useful for the high-throughput analysis of elastic and mechanical properties of materials. Program summaryProgram Title:MechElasticCPC Library link to program files:https://doi.org/10.17632/y9zc7zybrm.1Developer's repository link:https://github.com/romerogroup/MechElasticLicensing provisions: GPLv3Programming language: PythonNature of problem: To automatize and simplify the analysis of elastic and mechanical properties for bulk and 2D materials, especially for high-throughput DFT calculations.Solution method: This Python program addresses the above problem by parsing the elastic coefficient matrix obtained from the first-principles DFT calculations, does the appropriate post-processing to evaluate the elastic properties, and performs the mechanical stability tests for all crystal classes using the generalized Born-Huang criteria. It can also be used to carry out the equation of state analysis to study the structural phase transitions.Additional comments:MechElastic can be downloaded using the below link: https://github.com/romerogroup/MechElasticInstallation (via PyPI): pip install mechelastic, or pip3 install mechelastic

The Influence of Pressure on Structural, Elastic, Piezoelectric and Dielectric Properties of R3c‐BiAlO3 Based on Ab Initio Calculations

AbstractIn this paper, we deal with a theoretical and predictive study of the influence of the applied pressures on the structural, elastic and piezoelectric properties of the rhombohedral BiAlO3 perovskite (R3c space group) phase by combining both the density functional theory (DFT) and the density functional perturbation theory (DFPT) included in the ABINIT code. The results indicate a decrease in structural cell volume and the elastic constants appear to be more intense as the applied pressure increases. Due to the increase in the direct piezoelectric coefficient (e33) and the decrease of the elastic constant (c33), the converse piezoelectric coefficients (d33) tend to improve with increased pressure applied. At a pressure of 10 GPa, the value of the direct piezoelectric constant reached 6.23 C/m2 which becomes an indirect competitor to lead zirconate titanate (PZT). The dielectric constants and born effective charge at high pressure have been calculated. Our results agree well with the available experimental and theoretical results. Our findings, especially piezoelectricity, can help in various applications of high‐pressure devices such ultrasonic transducer.

First Principles Study of Structural Stability and Electronic Properties of CdTe Nanowires

This research article has explored the electronic behaviour of CdTe nanowire. The present study has evolved the structural dependence of electronic properties of CdTe nanowire. The shapes for which this dependence has been studied are 2 atoms linear, 2 atoms zigzag, 4 atoms square and 6 atoms hexagonal for CdTe nanowire. We have used ABINIT code for this study. We have explored the geometrical optimization, band structure and stability of proposed structures. The structure which has come out to be the most stable amongst the all is 4 atom square nanowire where as the findings of the study for band structure reveal that CdTe nanowires may have insulating as well semiconducting nature depending on the shape of the nanowire.

Modified Becke-Johnson calculations using norm-conserving pseudopotential plane-wave approach: Systematic analysis

The modified Becke-Johnson potential for exchange and local density approximation for correlation (mBJLDA) approach is proved to provide a highly improved description of the bandgap. This work presents the results of a systematic investigation of the mBJLDA electronic band structure calculations using the norm-conserving pseudopotential (PP) approach, as implemented in the ABINIT code. The considered systems represent different classes of semiconductors and insulators. Moreover, all-electron (AE) mBJLDA potential and screened hybrid functional YS-PBE0 calculations are also performed for comparison purposes. We show that the mBJLDA@PP bandgaps obtained using typical PP's (i.e., valence and semicore electrons are allowed to relax) are generally speaking smaller than that of the mBJLDA@AE approach. This artifact cannot be attributed to a small “c” parameter of the mBJLDA, since we found that this parameter is quite insensitive to the adopted computational method. Interestingly, the number of electrons treated as valence, especially for the cations, can be used as an extra adjustable parameter to improve the mBJLDA@PP bandgaps. In particular, the best agreement with the mBJLDA@AE bandgaps is obtained by including the outer core p electrons as valence. The optimal PP's for mBJLDA@PP calculations are transferable. A similar agreement is also achieved for the binding energies of the semicore d electrons (in the IIB-VI and IIIB-V compounds), upper valence bandwidths and electron effective masses. Sound explanations of the mBJLDA@PP results for the considered electronic structure properties are provided.

First-principles insights on the stability, linear and nonlinear optical properties of new potential thioborates AgBS2, CuBS2

Thioborates compounds are receiving increasing attention due to their numerous optical applications. In this work, we present a theoretical prediction of physical properties of CuBS2 and AgBS2 compounds by mean the density functional theory using the pseudo potential plane-wave method implemented in ABINIT and CASTEP codes. We investigated the structure stability and other ground state properties. The dynamical stability is also discussed from the phonon dispersion for the new hypothetical phase. We used the hybrid functional to estimate the band gap. Moreover, we present the optical anisotropy and nonlinear optical properties, both studied compounds have wide band gap, adequate optical birefringence and good second order NLO coefficients, which make them potential candidates for NLO applications.

Prediction of the structural, electronic, and piezoelectric properties of narrow-bandgap compounds FeVX (X = P, As, Sb)

A systematic theoretical investigation is carried out on the possible piezoelectric effect in the half-Heusler FeVX (X = P, As, Sb) compounds crystallizing in the cubic MgAgAs-type structure C1b by combining density functional theory (DFT) and perturbation theory (DFPT) based on the pseudopotential plane wave (PP-PW) method implemented in the ABINIT code. The ground-state properties such as the lattice constants, and the bulk modulus and its pressure derivative are obtained using both the local density approximation and the generalized gradient approximation for the exchange–correlation functional, and the results are compared with other studies. The results for the electronic properties reveal that all the compounds exhibit semiconducting behavior with a narrow indirect bandgap. In addition, the elastic, dielectric, and piezoelectric constants are computed using density functional perturbation theory. The title compounds are found to exhibit a good electromechanical coupling coefficient (k14). No experimental or theoretical data are available for their piezoelectric properties. Thus, the results of this study can be considered to represent theoretical predictions of the properties of new piezoelectric half-Heusler compounds that can be selected based on the values of their piezoelectric coefficient (e14), which are greater than the value of 0.16 C/m2 measured empirically for GaAs. Finally, the results presented herein shed light on the use of such piezoelectricity as a possible effect in various applications such as micromechanical actuators, sensors, and self-powered devices.

First-principles investigation on the stability and material properties of all-inorganic cesium lead iodide perovskites CsPbI3 polymorphs

Cesium metal halide perovskites are very promising light absorbing materials for solar cells, due to their good thermal stability compared to other organometallic perovskites. Cesium lead iodide perovskite CsPbI3 is one the most promising compound from this family because of its band gap of 1.7eVsuitable for a top cell in silicon tandem solar cell. Herein, we systematically investigate the structural, electronic, elastic, optical properties and some carrier transport properties of CsPbI3 perovskites polymorphs using pseudo-potential plane wave method implemented in CASTEP and ABINIT codes. We use hybrid functional within the GW approximation (GW-HSE06) and the spin-orbit coupling (GGA-PBE + SOC) to estimate the band gaps. The elastic properties indicate the flexibility and softness of CsPbI3 perovskites, they also have a high absorption coefficient values (α = 104–105 cm−1) and low exciton binding energy which make them potential candidate for solar cells application.

Prediction of the Kinetic Properties of Sphalerite CdSexTe1−x (0.1 ≤ x ≤ 0.5) Solid Solution: an Ab Initio Approach

In the present paper, the interaction of electrons with different types of defects in sphalerite CdSexTe1−x (0.1 ≤ x ≤ 0.5) solid solution is considered. Analysis is carried out by using the short-range scattering models for electron interaction with eight kinds of point lattice defects. Calculation of the electron transition probabilities was made based on the wave function and self-consistent potential energy which were evaluated with the help of ABINIT code. For crystals with impurity concentrations 9.4 × 1014 – 1×1018 cm−3, the temperature dependencies of electron mobility and Hall factor in the range 15–1200 K are calculated. A comparative analysis of two competing approaches has been made: a short-range approach and a long-range approach (relaxation time approximation). It was found that these two approaches yield to essential qualitative and quantitative differences for theoretical temperature dependencies of electron mobility.

Ab Initio Study of Electronic Properties of Cadmium Sulphide Nanowires

In present study, we have explored CdS nanowire and their electronic properties for different structure. The study has been performed by ABINIT code. Four shapes under consideration were 2-atom linear, 2-atom zigzag, 4-atom square and 6-atom hexagonal nanowire. The geometric optimization, stability of different structures and band structure of the shapes has been studied. The findings reveal that four atom square nanowire structure is comparatively more stable than other structures whereas the study of band structure reveals that CdS nanowires may be conducting, semi conducting or insulating depending upon the geometrical shape of the nanowire.

Electron Mobility in CdSexTe1-x (x = 0.25) Solid Solution: Ab Initio Calculation

In this paper an assessment of the quality of a solid solution of CdSexTe1-x is done by study of its transport properties. The description of the kinetic phenomena is carried on the base of the wave function and self-consistent potential for solid solution CdSexTe1-x (x = 0.25) which were determined from the first principles using the projector augmented waves as implemented in the ABINIT code. The scattering processes were considered in the framework of short-range scattering models where the electron interaction with polar and nonpolar optical phonons, piezoelectric and acoustic phonons, static strain centers, neutral and ionized impurities was taken into account. The transition matrix elements were obtained by integration over the unit cell using three-dimensional B-spline interpolation. For crystals with impurity concentration 5.6´1015 - 5´1018 cm-3 the temperature dependences of electron mobility and Hall factor in the range 15 - 1200 K are calculated. The theoretical curves obtained in the short-range approach differ qualitatively and quantitatively from those obtained within the long-range models in relaxation time approximation.

PyProcar: A Python library for electronic structure pre/post-processing

The PyProcar Python package plots the band structure and the Fermi surface as a function of site and/or s,p,d,f - projected wavefunctions obtained for each k-point in the Brillouin zone and band in an electronic structure calculation. This can be performed on top of any electronic structure code, as long as the band and projection information is written in the PROCAR format, as done by the VASP and ABINIT codes. PyProcar can be easily modified to read other formats as well. This package is particularly suitable for understanding atomic effects into the band structure, Fermi surface, spin texture, etc. PyProcar can be conveniently used in a command line mode, where each one of the parameters define a plot property. In the case of Fermi surfaces, the package is able to plot the surface with colors depending on other properties such as the electron velocity or spin projection. The mesh used to calculate the property does not need to be the same as the one used to obtain the Fermi surface. A file with a specific property evaluated for each k-point in a k−mesh and for each band can be used to project other properties such as electron–phonon mean path, Fermi velocity, electron effective mass, etc. Another existing feature refers to the band unfolding of supercell calculations into predefined unit cells. Program summaryProgram Title: PyProcarProgram Files doi:http://dx.doi.org/10.17632/d4rrfy3dy4.1Licensing provisions: GPLv3Programming language: PythonNature of problem: To automate, simplify and serialize the analysis of band structure and Fermi surface, especially for high throughput calculations.Solution method: Implementation of a Python library able to handle, combine, parse, extract, plot and even repair data from density functional calculations. PyProcar uses color maps on the band structures or Fermi surfaces to give a simple representation of the relevant characteristics of the electronic structure.Additional comments: Features: PyProcar can produce high-quality figures of band structures and Fermi surfaces (2D and 3D), projection of atomic orbitals, atoms, and/or spin components.Restrictions: Only the VASP package is currently fully supported, the latest version of Abinit is partially supported (it will be fully supported in the Abinit versions 9.x). The PROCAR file format can easily be implemented within any DFT code.

Study of the linear and nonlinear response properties of the zinc-blende AlP, GaP and their AlxGa1-xP ternary alloys using first principle calculations

The structural, electronic, thermodynamic, vibrational, elastic, linear and nonlinear optical properties of AlxGa1-xP ternary alloys are studied using plane-wave pseudopotential method based on the density functional theory. The alchemical mixing method is used to construct an alloy by mixing the pseudopotentials in an appropriate way. The local density approximation is used for the exchange and correlation potentials calculations using the ABINIT code. The Born effective charges, phonon frequencies, longitudinal-transvers optical splitting and thermal properties are calculated using density functional perturbation theory. By applying the many-body effects within the Bethe-Salpeter approach using the Tam-Dancoff approximation, the frequency-dependent macroscopic dielectric function is calculated. The nonlinear dielectric (electronic) susceptibility, the electro-optic tensor and the Raman tensor are investigated in the framework of density functional perturbation theory using the 2n+1 theorem. Moreover, due to density functional theory band gap problem, the band-gap correction is performed within the one-shot GW approximation of many-body perturbation theory. The calculated results of AlP and GaP compounds are in acceptable agreement with available theoretical and experimental results, so the present study on the AlxGa1-xP alloys would be helpful for future experimental and theoretical investigations.

Theoretical prediction of the structural, elastic, electronic, and thermodynamic properties of the Nowotny-Juza LiMgAsxSb1-x alloy

We present a theoretical study of the structural, elastic, electronic and thermodynamic properties of the LiMgAsxSb1-x alloy in α-phase, from the density functional theory framework (DFT) and the pseudopotentials with planes waves approach, using the alchemical mixing approximation available in the ABINIT code. The lattice parameter, bulk modulus and elastic constants for the parent compounds LiMgAs and LiMgSb were found to agree reasonably with the available experimental and theoretical data. The compositional dependence of the lattice constant, bulk modulus, the elastic constants (Cij) and energy gap shows deviations from Vegard's law with differentiation of bowing parameters. We found that the LiMgAsxSb1-x alloy in α-phase are indirect semiconductors (Γ−X) for all concentrations. The origins of the gap bowing parameters were also examined using the approach of Zunger and co-workers. The variation of some thermodynamic proprieties as a function of the temperature for different Arsenic concentration have been predicted and discussed such as unit cell volume, Bulk modulus, Debye temperature, heat capacity at volume constant and thermal expansion coefficient.