Plane-wave Approach Research Articles

Structural properties of NaBeH3 material: Ab-initio calculations

Ab-initio calculations from first principle methods were performed toinvestigate the structural properties of perovskite-type hydride NaBeH3material. The pseudopotential plane-wave approach in the framework ofdensity functional theory (DFT) as implemented in the ABINIT codecomputer was used. The exchange-correlation functional for all elementsof our material of interest was described with the local densityapproximation (LDA). Our results of the equilibrium lattice parameter, thebulk modulus, and the pressure derivative of the bulk modulus of cubicNaBeH3 semiconducting material were found at around 3.335 Å (3.339Å), 65.64 GPa and 3.56, respectively. Our data are in good agreementwith the available theoretical data of the literature. In addition, the meltingpoint of our material of interest was calculated and found equal to 1217.45K. To the best of the authors' knowledge, no data is available in theliterature on the melting point of NaBeH 3 material.
 

First-principles calculations to investigate structural, electronic and phonon properties of sodium bromide (NaBr) and sodium iodide (NaI) crystals

In this paper, the first-principles study is performed to calculate the structural, electronic and phonon properties of alkali halides NaBr and NaI. The calculations for structural and electronic properties have been carried out using the full-potential linearized augmented plane-wave (FP-LAPW) method that is employed in the WIEN2k code, whereas the phonon properties are studied using the Quantum Espresso program based on density-functional theory within plane-wave fundamental sets and pseudo-potentials approaches. The calculation of structural, electronic band properties were carried out using generalized gradient approximation (GGA), local-density approximation (LDA) and a combination of modified Becke-Johnson exchange potential with LDA and GGA (TB-mBJ-GGA/LDA) for exchange-correlation potential. The calculated structural parameters are in good agreement with experimental results. In our electronic calculations, the obtained bandgaps are underestimated by LDA and GGA functionals compared to empirically derived results, which is an expected result. However, the calculated bandgaps by the modified Becke-Johnson exchange potential are in perfect agreement with the experiment. Finally, the dynamic properties of NaBr and NaI compounds were investigated. Both phonon dispersion and phonon density of states curves were calculated for compounds along with the high symmetry directions in the Brillouin region. The dynamical properties of NaBr and NaI crystals are analyzed and discussed.

High Pressure and Temperature Dependence of the Structural, Electronic, Thermal and Transport Properties of U3Si2: Computational Insights

Due to its advantageous thermophysical qualities, U3Si2 piques the interest of the nuclear industry as an accident‐tolerant fuel to replace uranium dioxide (UO2). Herein, the structural, electrical, thermodynamic, and transport features of the U3Si2 compound are investigated using the full‐potential linearized augmented plane wave approach within the density functional theory, and within the generalized gradient approximation related to spin orbit and Hubbard. The ground statistic parameters that are estimated, such as the lattice constants and bulk moduli, are qualitatively consistent with previous experimental and theoretical evidence. The density of states analysis reveals that U3Si2 is a metal complex. In addition, the macroscopic thermal effects of U3Si2 are calculated using the quasi‐harmonic Debye model, which includes lattice vibrations. Experimental and theoretical findings are compared with the calculated variations in volume, heat capacity, entropy, and Debye temperature as a function of temperature in the range of 0–1500 K. Some thermal properties are projected to be pressure dependent in the range of 0–20 GPa. In the temperature range of 0–1500 K, the semiclassical Boltzmann transport equation is utilized to estimate electron transport parameters such as the Seebeck coefficient, thermal and electrical conductivity.

First-principles study of half-metallic properties in X2CrAl (X = Co and Mn) FullHeusler and their quaternary MnCoCrAl and CoMnCrAl compounds

The full potential linearized augmented plane waves (FP- LAPW) approach is used to investigate the structural, electronic, and magnetic properties of full-Heusler alloys X2CrAl (X = Co and Mn) and their quaternary compounds MnCoCrAl and CoMnCrAl. The density of states (DOS) of Co2CrAl, Mn2CrAl, and related quaternary compounds reveal the existence of energy band gaps with half-metallic behavior based on GGA and mBJ exchange–correlation potential.All full-Heusler materials and their quaternary compounds have total magnetic moments that agree well with the Slater Pauling rule. Mechanical properties of these compounds are also researched, including bulk modulus, shear modulus, Young's modulus, Poisson's ratio, and Pugh's ratios, and all studied compounds display mechanical stability under the mechanical stability criterion. Our findings provide experimental researchers with suggestions for synthesizing promising materials for future spintronic applications.

A first-principles study of optoelectronic properties of Y2MS4 (M=Zn, Mg and Be): Direct bandgap ternary sulfides

The optoelectronic properties of the ternary sulfides Y2MS4 (M = Zn, Mg, and Be) are explored using computational techniques. The lattice parameters and electro-optical properties have been investigated with a full-potential linearized augmented plane wave (FP-LAPW) approach using the Generalized Gradient Approximation (GGA) through density functional theory (DFT). The TB-mBJ is utilized to compute electronic bandgap because it is reported as decent functional to generate a bandgap more accurately. The electronic band structure profile revealed the direct bandgap of 1.90, 2.61, and 1.85 eV for Y2ZnS4, Y2MgS4, and Y2BeS4, respectively. These ternary sulfides show good absorption and reflectivity in ultraviolet region of light, highlighting these sulfides' capability as a shield against ultraviolet radiation. The results of our calculations revealed the potentials of these ternary spinal sulfides Y2MS4 (M = Zn, Mg, and Be) for photovoltaic applications.

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.

Structural, electronic and elastic properties of FeCrAs Half-metallic ferromagnetic Half-Heusler Alloy: A First-Principles study

In this work, we employ full potential linearized augmented plane wave approach based on the density functional theory to calculate the structural, electronic, and elastic properties of FeCrAs Half-Heusler compound. For electron exchange, we have considered the most common Generalized Gradient Approximation (PBE-GGA and PBEsol-GGA), as exchange and correlation potential for investigating these properties. The half-metallic ferromagnetic behavior is confirmed by density of states and spin-polarized band structures analysis, which show that the FeCrAs has an indirect band-gap in the spin-down channel and a metallic behaviour in the spin-up channel. Furthermore, the elastic constants (Cij) and the related elastic moduli confirm their stability in the cubic phase and demonstrate their brittle nature. The Debye’s temperature along with compressional, Shear and average elastic wave velocities has also been calculated.[copyright information to be updated in production process]

First-principles calculations to investigate structural, mechanical, electronic, magnetic and thermoelectric properties of Ba2CaMO6 (M=Re, Os) cubic double perovskites

Structural, mechanical, electronic, magnetic and thermoelectric characteristics of Ba2CaMO6 (M = Re, Os) double perovskites have been calculated using first-principle based full-potential linearized augmented plane wave (FP-LAPW) approach. Optimized ground-state lattice constants of the compounds are in fair resemblance with the respective available experimentally investigated data. Calculated elastic constants and moduli show mechanical stability, anisotropy, ductility and significant stiffness. Computed spin-polarized electronic properties with a diversity of exchange-correlation potential schemes have revealed their half-metallic nature. Estimated spin magnetic moments indicate their ferromagnetic nature with major contributions from the 5d state of transition elements Re and Os. The present study has projected both the perovskite compounds as prospective magnetic materials for a variety of half-metallic, ferromagnetic and spintronic applications. Calculated thermoelectric parameters have predicted their scope of thermoelectric applications in high temperature waste heat management.

Electronic structure and optical response of double perovskite Rb2NaCoF6 for optoelectronic devices

The bonding nature, structural, electrical, and optical properties of Rb2NaCoF6 has been investigated using density functional theory (DFT) calculations in this communication. The results are based on the total energy calculations using density functional theory by employing the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) approach. A direct band gap of 1.5eV is observed along (X−X) points with generalized gradient approximation (GGA). The improvement in the band gap i.e. 2.2eV is achieved with modified Becke-Johnson potential. The total and partial density of states shows a good agreement with the band structure. The bonding nature of the compound is studied with a contour plot of electron density. Further emphasis has been given to Rb2NaCoF6 hexaflouroperovskite absorption and reflection spectra, which reveal substantial absorption and reflection in the ultraviolet region. From the current work in Rb2NaCoF6, it is expected that the numerous quantum mechanical phenomena would be able to provide a better understanding in designing the practical devices.

Digital orbitals: connecting the tight-binding and plane-wave approaches through sampled-real-space models

Discrete approximations to continuous systems have proven valuable in many areas of physics and engineering. Discrete real-space calculations are often used in electronic structure calculations for molecules, and have been used in electronic structure calculations for crystals. Besides their computational utility, they can be used to connect the plane-wave and tight-binding methods of crystalline electronic structure calculations. A fully discrete-space approach results in exactly equivalent, finite, plane-wave and tight-binding bases for the same crystal because the two bases therefore span exactly the same space. Beyond connecting the two methods, the fully discrete approach addresses important issues in tight-binding. First, it results in a fully gauge invariant position operator capable of sub-cell spatial resolution. Second, it explains the observation in tight-binding that a small basis with long-range couplings and a large basis with short-range couplings can often reproduce technologically relevant bands with comparable accuracy.

Structural, Electronic, Magnetic Properties and Elastic Anisotropy of New Ferromagnetic Cu2CrZ (Z=Si and Ge) Full Heusler Alloys

In this paper, we have performed a first-principles study to investigate the electronic structure, magnetic, mechanic and anisotropic elastic properties of Cu2CrZ (Z=Si and Ge) Full Heusler alloys. The study of these characteristics shows thermodynamic and mechanical stability with cubic symmetry in our compounds and they also have an anisotropic character. The ground-state parameters, i.e., lattice constant, the bulk modulus and the electronic structure are calculated using the full-potential linearized augmented plane wave (FP-LAPW) approach to the density functional theory (DFT) within the generalized gradient approximation (GGA+WC) for the exchange and correlation potential. The objective is to seek stable metallic ferromagnet materials.

Effect of Sr - Transition Metal Substitution on Electronic and Mechanical Properties of Mg2Si: A DFT Study

Abstract: Recently, magnesium alloys have attracted scientific interest due to their technological importance in thermoelectric, piezoelectric, photo-voltaic and infrared photonics applications. The electronic and elastic properties of MgXSi (X = Mg, Sr) compounds were investigated in this work, using the density functional theory (DFT) with pseudo-potential plane-waves (PPW) approach as implemented in Quantum Espresso code. The results of the elastic constants of Mg2Si are in agreement with the previous theoretical results and favourably compared with experimental data. The electronic band structures of these semiconductors were calculated to give narrow indirect and direct band gaps of Mg2Si and MgSrSi, respectively. Our results show that the two compounds are mechanically stable. The Pugh’s ratio, B/G, indicated that Mg2Si and MgSrSi are brittle and ductile in nature. The estimated anisotropy parameter, A, shows that Mg2Si has a higher degree of elastic isotropy in comparison to MgSrSi. Three-dimensional (3D) projection of Young’s modulus and area modulus of the compounds was presented. Keywords: Electronic structure, Elastic constants, Mechanical properties, Mg2Si, MgSrSi. PACS: 31.15.A-, 62.20.F-, 71.55.-i, 71.20.Be.

Ab initio DFT determination of structural, mechanical, optoelectronic, thermoelectric and thermodynamic properties of RbGeI3 inorganic perovskite for different exchange-correlation functionals

As a potential counterpart to the toxic CH3NH3PbI3 for photovoltaic applications, a lead-free non-toxic perovskite, rubidium germanium iodide (RbGeI3) is analyzed to assess its structural, mechanical, elastic, optoelectronic, thermoelectric and thermodynamic properties using the Full-Potential Augmented Plane Wave (FP-LAPW) approach of the WIEN2k code using density functional theory. Though various exchange correlation functionals viz. the Perdew Burke Ernzerhof scheme of Generalized Gradient Approximation (PBE-GGA), PBEsol, and WC-GGA are used, the TB-mBJ exchange correlation potential coupled with GGA, provides enhanced results. The lattice constants a0, bulk modulus B and its pressure derivative Bp are estimated to be 11.619096 bohr, 19.34 GPa and 5.4303 respectively with TB-mBJ exchange correlation potential. The elastic constants, C11, C12 and C44, Young’s modulus E, Shear modulus G, Poisson’s ratio ν and Anisotropic ratio A are estimated to be 43.4 GPa, 7.3 GPa, 7.9 GPa, 27.93 GPa, 11.09 GPa, 0.26 and 0.07 respectively using the Elastic 1.0 package. The density of states (DOS) and band structure are plotted for various exchange correlation functionals. The energy band gap and the absorption coefficient of the material, 1.338 eV and 10−3 cm−1 respectively, are found to be suitable for photovoltaic applications. Various thermoelectric coefficients like Seebeck coefficient, electrical conductivity and thermal conductivity are also calculated. The thermodynamic properties like Debye temperature, heat capacity, entropy and thermal expansion coefficient are plotted as a function of temperature and pressure using Gibbs2 program. The study indicates that inorganic cubic RbGeI3 has all the characteristics required as an absorber material for perovskite solar cells. However, the phonon dispersion spectrum shows the presence of imaginary modes indicating an instability in the structure with rise in temperature.

Electronic Structure of Molecules, Surfaces, and Molecules on Surfaces with the Local Modified Becke-Johnson Exchange-Correlation Potential.

The knowledge of electronic properties of matter is the key to the understanding of its properties and to propose useful applications. To model hybrid organic/inorganic systems with the plane-wave approach, large supercells with many atoms are usually necessary to minimize artificial interactions between periodic images. For such systems, accurate approximations to the exchange-correlation functional of density functional theory, such as hybrid functionals, become computationally expensive, and cheaper approaches need to be considered. Here, we apply the local modified Becke-Johnson exchange-correlation potential to free molecules and surfaces and study its accuracy for calculated ionization potentials. This quantity being important to understand the band alignment of composite heterogeneous systems, we demonstrate the application of the potential to the electronic structure calculation of an exemplary composite semiconductor/molecule system, namely, a F6-TCNNQ molecule adsorbed on a hydrogenated Si(111) surface.

Scattering problems via real-time wave packet scattering

In this paper, we use a straightforward numerical method to solve scattering models in one-dimensional lattices based on a tight-binding band structure. We do this by using the wave packet approach to scattering, which presents a more intuitive physical picture than the traditional plane wave approach. Moreover, a general matrix diagonalization method that is easily accessible to undergraduate students taking a first course in quantum mechanics is used. Beginning with a brief review of wave packet transport in the continuum limit, comparisons are made with its counterpart in a lattice. The numerical results obtained through the diagonalization method are then benchmarked against analytic results. The case of a resonant dimer is investigated in the lattice, and several resonant values of the mean wave packet momentum are identified. The transmission coefficients obtained for a plane wave incident on a step potential and rectangular barrier are compared by investigating an equivalent scenario in a lattice. Finally, we present several short simulations of the scattering process, which emphasize how a simple methodology can be used to visualize some remarkable phenomena.

Beam-normal single-spin asymmetry in elastic scattering of electrons from a spin-0 nucleus

We study the beam-normal single-spin asymmetry (BNSSA) in high-energy elastic electron scattering from several spin-0 nuclei. Existing theoretical approaches work in the plane-wave formalism and predict the BNSSA to scale as $\ensuremath{\sim}A/Z$ with the atomic number $Z$ and nuclear mass number $A$. While this prediction holds for light and intermediate nuclei, a striking disagreement in both the sign and the magnitude of BNSSA was observed by the PREX collaboration for $^{208}\mathrm{Pb}$, coined the ``PREX puzzle.'' To shed light on this disagreement, we go beyond the plane-wave approach which neglects Coulomb distortions known to be significant for heavy nuclei. We explicitly investigate the dependence of BNSSA on $A$ and $Z$ by (i) including inelastic intermediate states' contributions into the Coulomb problem in the form of an optical potential, (ii) by accounting for the experimental information on the $A$-dependence of the Compton slope parameter, and (iii) giving a thorough account of the uncertainties of the calculation. Despite of these improvements, the PREX puzzle remains unexplained. We discuss further strategies to resolve this riddle.

Path Loss Models for Wireless Cardiac RF Communication

In this letter, we propose fundamental path loss (PL) models which play vital roles in promoting the intraheart communication system design of future deeply implanted leadless pacemakers inside the cardiac chambers. Initially, employing a plane wave approach yields the attenuation of the electric field in homogeneous heart tissue, while a modified Friis equation in the lossy medium is utilized to evaluate the power transmission between transmitting and receiving antennas in homogeneous heart tissue in the far-field zone. An Hertzian dipole excitation is used to separate the mismatch and ohmic losses of the antenna from the path loss in an anatomical human body simulation environment. Based on this theoretical and full-wave simulation setup, PL models are derived and comprehensively compared at different potential frequency bands [Medical Implant Communication Service (MICS) 402-405 MHz, Wireless Medical Telemetry Service (WMTS) 608-614 MHz, Industrial, Scientific, and Medical (ISM) 867-869 MHz, and 2400-2500 MHz], and the validity of applying the Friis equation in this scenario is verified.

Classical Casimir free energy for two Drude spheres of arbitrary radii: A plane-wave approach

We derive an exact analytic expression for the high-temperature limit of the Casimir interaction between two Drude spheres of arbitrary radii. Specifically, we determine the Casimir free energy by using the scattering approach in the plane-wave basis. Within a round-trip expansion, we are led to consider the combinatorics of certain partitions of the round trips. The relation between the Casimir free energy and the capacitance matrix of two spheres is discussed. Previously known results for the special cases of a sphere-plane geometry as well as two spheres of equal radii are recovered. An asymptotic expansion for small distances between the two spheres is determined and analytical expressions for the coefficients are given.

Analytic calculation and analysis of atomic polar tensors for molecules and materials using the Gaussian and plane waves approach.

The evaluation of atomic polar tensors and Born Effective Charge (BEC) tensors from Density Functional Perturbation Theory (DFPT) has been implemented in the CP2K code package. This implementation is based on a combination of the Gaussian and plane wave approach for the description of basis functions and arising potentials. The presence of non-local pseudo-potentials has been considered, as well as contributions arising from the basis functions being centered on the atoms. Simulations of both periodic and non-periodic systems have been implemented and carried out. Dipole strengths and infrared absorption spectra have been calculated for two isomers of the tripeptide Ser-Pro-Ala using DFPT and are compared to the results of standard vibrational analyses using finite differences. The spectra are then decomposed into five subsets by employing localized molecular orbitals/maximally localized Wannier functions, and the results are discussed. Moreover, group coupling matrices are employed for visualization of results. Furthermore, the BECs and partial charges of the surface atoms of a periodic (101) anatase (TiO2) slab have been investigated in a periodic framework.

The correlation between experimental polarized Raman spectra and their density functional theory prediction in the LCAO framework: The R3c LiNbO3 crystal as a test case

AbstractIn this study, the polarized Raman spectra of the R3c LiNbO3 crystal are used as a benchmark test for density functional theory (DFT) full periodic boundary conditions linear combination of atomic orbitals (LCAO) calculation of the Raman tensors, according to the implementation in the CRYSTAL software. The theoretical approach used proved to provide excellent results regarding wavenumbers and relative intensities predictions for the transverse optical modes of both A1 and E symmetry, considerably improving over previously reported data based on the plane waves approach. Overall, the present investigation demonstrates that the LCAO approach, as implemented in the CRYSTAL software, gives excellent results regarding the calculation of Raman tensors and polarized Raman spectra. The possibility to put in correspondence the individual Raman tensors components and bands intensities in the different back‐scattering experimental configurations revealed that the computed Raman tensors are very accurate, not only considering their average values (tensors invariant in the combination suitable for the description of Raman scattering of isotropic materials) but also when the tensors individual components are considered. Based on the present results, a reassignment of the E (TO) modes of the R3c LiNbO3 crystal is proposed, in particular for the 2 E and 9 E modes, which have been a matter of discussion in the recent years.