Pseudopotential Plane Wave Research Articles

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.

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.

First-principles calculations to investigate structural, electronics, optical and elastic properties of Sn-based inorganic Halide-perovskites CsSnX3 (X = I, Br, Cl) for solar cell applications

The structural, electronic, optical, and elastic properties of cubic inorganic-perovskites CsSnX3 (where X = I, Br, Cl) based on Sn were investigated using a Density Functional Theory (DFT) based Cambridge Serial Total Energy Package (CASTEP) code with Ultrasoft Pseudo-Potential (USP) plane-wave and Perdew-Burke-Ernzerhof (PBE) exchange–correlation function of the Generalized Gradient Approximation (GGA). The calculated lattice parameters and band gap match well with the previous studies. These materials have a direct and narrowband gap and can be utilized to increase the conductivity. All the compounds are found anisotropic and ductile according to the anisotropic factor and Poisson’s ratio, respectively. These compounds have high optical absorption and conductivity, according to optical characteristics, andhave been discovered to be a promising contender for solar cell applications. Due to their direct band gap, these materials are also suitable for light-emitting diodes (LED) and other reflectivity purposes. CsSnI3 may be a better choice for LEDs and solar cells due to its narrower band gap.

Spin-Orbit Coupling and Spin-Polarized Electronic Structures of Janus Vanadium-Dichalcogenide Monolayers: First-Principles Calculations.

Phonon and spintronic structures of monolayered Janus vanadium-dichalcogenide compounds are calculated by the first-principles schemes of pseudopotential plane-wave based on spin-density functional theory, to study dynamic structural stability and electronic spin-splitting due to spin-orbit coupling (SOC) and spin polarization. Geometry optimizations and phonon-dispersion spectra demonstrate that vanadium-dichalcogenide monolayers possess a high enough cohesive energy, while VSTe and VTe2 monolayers specially possess a relatively higher in-plane elastic coefficient and represent a dynamically stable structure without any virtual frequency of atomic vibration modes. Atomic population charges and electron density differences demonstrate that V–Te covalent bonds cause a high electrostatic potential gradient perpendicular to layer-plane internal VSTe and VSeTe monolayers. The spin polarization of vanadium 3d-orbital component causes a pronounced energetic spin-splitting of electronic-states near the Fermi level, leading to a semimetal band-structure and increasing optoelectronic band-gap. Rashba spin-splitting around G point in Brillouin zone can be specifically introduced into Janus VSeTe monolayer by strong chalcogen SOC together with a high intrinsic electric field (potential gradient) perpendicular to layer-plane. The vertical splitting of band-edge at K point can be enhanced by a stronger SOC of the chalcogen elements with larger atom numbers for constituting Janus V-dichalcogenide monolayers. The collinear spin-polarization causes the band-edge spin-splitting across Fermi level and leads to a ferrimagnetic order in layer-plane between V and chalcogen cations with higher α and β spin densities, respectively, which accounts for a large net spin as manifested more apparently in VSeTe monolayer. In a conclusion for Janus vanadium-dichalcogenide monolayers, the significant Rashba splitting with an enhanced K-point vertical splitting can be effectively introduced by a strong SOC in VSeTe monolayer, which simultaneously represents the largest net spin of 1.64 (ћ/2) per unit cell. The present study provides a normative scheme for first-principles electronic structure calculations of spintronic low-dimensional materials, and suggests a prospective extension of two-dimensional compound materials applied to spintronics.

First principle study of the electronic and structural properties of NaFeAs superconductor

In this paper, the detailed electronic structure of NaFeAs compound i.e., the band structure calculation, density of states along with the partial density of states are examined with the first principle density functional approach. The system NaFeAs is a member of iron-based superconductors of 111-family. It exhibit superconducting transition at 12–25 K at ambient condition. The crystal structure of this compound is a tetragonal type structure and here we did the self-consistent calculation using the PWSCF-Quantum ESPRESSO code. The total energy and the electronic calculations of the system can be examined by plane wave pseudopotentials. Here the electronic band structure diagram, partial density of states and the total density of states of NaFeAs were studied. From the band structure diagram the metallic behaviour of the compound is observed and from the projected density of state, the electronic states are found to be predominant by the iron atom near the Fermi region.

Effect of Pressure on Electronic and Optical Properties of SrAl2O4

The effect of pressure on the electronic and optical properties of SrAl2O4 up to 25 GPa was studied by means of the pseudo-potential plane waves method within the generalized gradient approximation for exchange and correlation. The calculated lattice parameters are consistent with available experimental and theoretical data. By analyzing the electronic and optical properties, the pressure dependences of the electronic structures and optical constants were investigated. The band structures show an indirect band gap for this compound and the calculated band gaps expend with increasing pressure. Meanwhile, the optical properties including the dielectric spectra, absorption coefficient spectra, reflectivity, and the real part of the refractive index spectra in the low energy range have a blue shift. Given this, the optical properties of SrAl2O4 could be tuned by changing pressure to some degree, which is beneficial to the optical applications.

First principles calculation of electronic properties and effective mass of zinc-blende GaN

Based on the first principle pseudopotential plane wave method, the electronic structure of zinc-blende semiconductor GaN is calculated. Using the relativistic treatment of valence states, the spin orbit splitting energy of valence band top near the center of Brillouin region is calculated. Based on the effective mass approximation theory, the effective mass of electrons near the bottom of the conduction band and the effective mass of light and heavy holes near the Γ point along the directions of [100], [110] and [111] are calculated. These parameters are valuable and important parameters of optoelectronic materials.

First-principles study of calcium-based sulfur fixers and their products

Calcium-based sulfur-fixing agent, as the main sulfur-fixing product, is widely used in power plant boiler systems. In order to further study the thermodynamic properties and reaction characteristics of calcium-based sulfur fixing agent and its products, the method of combining power plant experiment with theory was used. The electronic structure, thermodynamic properties and density of states of quicklime, limestone, calcium sulfate (CaSO4) and calcium sulphoaluminate have been calculated based on the first-principles ultra-soft pseudopotential plane wave method of density functional theory. The generalized gradient approximation algorithm is used to optimize the structure of various minerals to achieve the most stable state. The results show that the enthalpy, entropy, specific heat capacity at constant pressure and Gibbs free energy of calcium sulfonate vary greatly from 25-1000 K, while the change of calcium oxide (CaO) is small, and that of calcium carbonate (CaCO3) and CaSO4 are between them. It shows that calcium sulphoaluminate has strong stability and more energy is needed to destroy the molecular structure of calcium sulphoaluminate. The CaO is the most unstable and requires less energy to react. The CaCO3 and CaSO4 are in between. The variation range of CaSO4 is greater than that of CaCO3, indicating that the stability of CaSO4 is higher than that of CaCO3. The experimental results show that the desulfurization efficiency of generating calcium sulphoaluminate is much higher than that of only generating CaSO4, indicating that calcium sulphoaluminate is very stable, which is consistent with the calculated results.

First-principles calculations to investigate ultra-wide bandgap semiconductor behavior of NaMgF3 fluoro-perovskite with external static isotropic pressure and its impact on optical properties

The structural, electronic, and optical properties of cubic fluoro-perovskite NaMgF3 were investigated theoretically at pressures ranging from 0 to 100 GPa with a 10-step escalation, i.e., 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 GPa. The research is conducted by using density functional theory (DFT) based CASTEP (Cambridge Serial Total Energy Package) code with ultra-soft pseudo-potential USP plane wave and Perdew Burke Ernzerhof (PBE) exchange-correlation functional of Generalized Gradient Approximation (GGA). The band gap is found to be increasing from 5.749 to 8.723 eV when the pressure is increased from 0 to 100 GPa. The nature of the band gap remained indirect whether the pressure was applied or not. A significant increment was found in the band gap till 40 GPa as compared to higher pressure. Under the effect of pressures ranging from 0 to 100 GPa, several optical properties like the refractive index, loss function, reflectivity, and absorption coefficient have also been determined. The main peaks of dielectric function (real and imaginary), reflectivity, loss function, and refractive index (n) are observed to move towards higher values of energy with increasing pressure. A material that has a high optical conductivity, absorption, and refractive index is ideal for photovoltaic applications. Other optical technologies that use such material include waveguides, data storage medium, and photonic crystals.

Engineering the hydrogen storage properties of the perovskite hydride ZrNiH3 by uniaxial/biaxial strain

In the present work, the bonding length, electronic structure, stability, and dehydrogenation properties of the Perovskite-type ZrNiH3 hydride, under different uniaxial/biaxial strains are investigated through ab-initio calculations based on the plane-wave pseudo-potential (PW-PP) approach. The findings reveal that the uniaxial/biaxial compressive and tensile strains are responsible for the structural deformation of the ZrNiH3 crystal structure, and its lattice deformation becomes more significant with decreasing or increasing the strain magnitude. Due to the strain energy contribution, the uniaxial/biaxial strain not only lowers the stability of ZrNiH3 but also decreases considerably the dehydrogenation enthalpy and decomposition temperature. Precisely, the formation enthalpy and decomposition temperature are reduced from −67.73 kJ/mol.H2 and 521 K for non-strained ZrNiH3 up to −33.73 kJ/mol.H2 and 259.5 K under maximal biaxial compression strain of ε = −6%, and to −50.99 kJ/mol.H2 and 392.23 K for the maximal biaxial tensile strain of ε = +6%. The same phenomenon has been also observed for the uniaxial strain, where the formation enthalpy and decomposition temperature are both decreased to −39.36 kJ/mol.H2 and 302.78 K for a maximal uniaxial compressive strain of ε = - 12%, and to −51.86 kJ/mol.H2 and 399 K under the maximal uniaxial tensile strain of ε = +12%. Moreover, the densities of states analysis suggests that the strain-induced variation in the dehydrogenation and structural properties of ZrNiH3 are strongly related to the Fermi level value of total densities of states. These ab-initio calculations demonstrate insightful novel approach into the development of Zr-based intermetallic hydrides for hydrogen storage practical applications.

Density function theory on the electronic structure property of anatase TiO2 doped by N or C with different percents

Formation energy, crystal structure and electronic structure of C, N doped anatase TiO2 are calculated based on the density functional theory of plane-wave ultrasoft pseudopotential. Results indicate that, due to doping of the C or N atoms in anatase TiO2, the lattice distorts obviously. The substitution of C tends to Ti site while N tends to O site. All the substitutions lead to the red shift of the optical absorption and increasing coefficient of light absorption. When N concentrations are 2.08% and 3.13% in N-doped TiO2, the highest photocatalytic activity is obtained, while it is 2.08% for C-doped one.

Static isotropic pressure induced ultra-wide band gap response of NaCaF3 fluoro-perovskite and its repercussions on optical properties: ab initio calculation

ABSTRACT A comprehensive theoretical study to investigate the outcomes of externally applied static isotropic pressure (0–50 GPa) on electronic, optical and structural properties of NaCaF3, using density functional theory based CASTEP code with ultra-soft pseudo-potential USP plane wave and Perdew Burke Ernzerhof exchange–correlation functional of Generalized Gradient Approximation, is reported. The electronic band gap shows the increasing trend 4.773–6.203 eV with increasing external pressure. The increase in band gap is significant up to 20 GPa as compared to higher external pressures. The mystery of increasing band gap is nicely decoded by the total density of states and elemental partial density of states. Optical properties have been calculated to analyse the impact of increment in band gap on them. We observed that the highest peak of energy loss function shows the blue shift which confirms the increment of band gap. At zero photon energy, for 0 GPa, the static refractive index has a value of 1.4456. After applying external pressure, there is a slight increase in which favours the ultrawide band gap behaviour of the ternary compound. The energy points at which the absorption peak is maxima, the refractive index has lowest value.

Fundamental Physical Properties of LiInS2 and LiInSe2 Chalcopyrite Structured Solids

For the couple of chalcopyrite compounds, we have theoretically studied the various properties for example structural, electronic optical and mechanical properties. The band structure curve, the density of states as well as the total energy have been investigated with the help of ATK-DFT by using the pseudo-potential plane wave method. For the LiInS2 and LiInSe2 chalcopyrites, we have found that these compounds possess direct band gap; which is 3.85 eV and 2.61 eV for LiInS2 and LiInSe2 respectively. It shows that the band gap is decreasing from ‘S’ to ‘Se’ as well as the B/G ratio called Pugh’s ratio is 2.10 for LiInS2 and 2.61 for LiInSe2 so these compounds are ductile in nature also these compounds are found to be mechanically stable. The study of this work display that the couple of these chalcopyrite compounds can be the promising candidate for the substitution of absorbing layer in the photovoltaic devices.

Significant improvement in the piezoelectric properties and electromechanical coupling factors of wurtzite AlN compound under high pressures

This work describes a theoretical study of the pressure effect in structural, elastic, piezoelectric and dielectric properties as well as electromechanical coupling factors of wurtzite AlN, obtained by ab-initio calculations using pseudo-potential plane waves (PP-PW) that combine the density functional theory (DFT) and density functional perturbation theory (DFPT). The results of the calculation indicate that the parameters of AlN crystal cells and the volume of AlN crystalline crystal cells decrease notably with increasing pressures from 0 to 40 GPa. Due to an increase in the value of the direct piezoelectric constant (\({e}_{33})\) and a decrease in the value of the elastic constant (\({C}_{33}\)), there is a significant improvement in the value of the converse piezoelectric constant (\({d}_{33}\)). The improvement in the piezoelectric value leads to a higher value in electromechanical coupling coefficient. Our results agree well with previous theoretical and experimental research. We hope that our results will provide guidelines for the realistic application as well as further research of high-performance compounds appropriate for applications in a multitude of fields of study, such as biomedical engineering.

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.

Effect of Hydrostatic pressure on structural, electronic, optical and mechanical properties of Lanthanum Oxide (La2O3)

Effect of pressure variation on structural, electronic, optical, and mechanical properties of lanthanum oxide (La2O3) have been investigated by using Cambridge Serial Total Energy Package (CASTEP) under reference of density functional theory (DFT) for ab initio calculations with plane wave basis set and pseudopotentials. The complete investigation of material demands calculations of many nuclei system on quantum scale and many nuclei system needs large simulations to predict accurate answers. DFT offers feasible solution of this complexity and allows investigation of materials on quantum scale accurately and precisely by considering electron density and finite k-points in Brillouin Zone (BZ).La2O3 is compressible under the effect of applied high pressure but not offer any phase or structural transformation state 0 GPa to 50 GPa. The properties of lanthanide materials can be controlled to a large extent and relative energy by considering behavior of 4f and 5d electrons behavior. The application of pressure from 0 to 50 GPa reveals a predominant characteristic associated with narrowing of bandgap. All the calculated optical properties such as the complex dielectric function ε(ω), optical conductivity σ(ω), energy loss function L(ω), absorption coefficient α(w), refractive index n (ω), reflectivity R (ω), and effective number of electrons neff, via sum rules shift towards the lower energies under the application of pressure. The influence of pressure on elastic constants and their related mechanical parameters have been discussed in detail.

Structural, electronics and optical properties of sodium based fluoroperovskites NaXF3 (X = Ca, Mg, Sr and Zn): First principles calculations

A theoretical study to investigate the electronic, optical and structural properties of sodium-based cubic fluoro-perovskite NaXF3 (where X = Ca, Mg, Sr, Zn), using density functional theory (DFT) based CASTEP (Cambridge Serial Total Energy Package) code with ultra-soft pseudo-potential USP plane wave and Perdew Burke Ernzerhof (PBE) exchange-correlation functional of Generalized Gradient Approximation (GGA), is reported. All of these compounds are found to be in a stable shape with a cubic pm3m structure, according to the findings. The results we discovered are consistent with the data that is already available. Calculations of the electronic band structure show that NaCaF3, NaMgF3 and NaSrF3 have a direct and NaZnF3 has an indirect band gap. Partial density of states (PDOS) and total density of states (TDOS) confirm the degree of electron localization in various bands. All four compounds' optical transitions were investigated by fitting the dispersion relation for the hypothetical dielectric function scale to the corresponding peaks. NaZnF3 is semiconductor while the NaCF3, NaMgF3 and NaSrF3 compounds have insulating behavior. The hypothetical part dispersion of the dielectric function reveals its wide range of energy transparency. As a result, it's possible that these materials may be used in optoelectronics to absorb ultraviolet light.

Thermodynamic evidence of the ferroelectric Berry phase in europium-based ferrobismuthite Eu2Bi2Fe4O12

The possible low temperature biferroic feature of Eu2Bi2Fe4O12 complex perovskites was recently reported. The aim of this work is to present a theoretical study of the structural, magnetic, electronic and ferroelectric properties of this material. Several energy minimization processes were performed for three types of cationic distributions, different angles of rotation, octahedral inclination, and some kinds of magnetic ordering. The results reveal that the most stable crystallographic arrangement corresponds to an intercalated distribution of the Eu3+ and Bi3+ cations between the FeO6 octahedra. Similarly, energy is minimized for rotations and octahedral inclinations corresponding to angles θe = 12.86° and ϕe= 13.32°, respectively. With respect to the distribution of magnetic moments, the results reveal that a G-type antiferromagnetic configuration is the most energetically favorable. The electronic structure is studied from ab initio calculations following the formalism of density functional theory and the pseudopotential plane wave method. In this formalism, the exchange and correlation mechanisms are described by means of the generalized gradient approach (GGA + U), considering spin polarization. The ferroelectric characteristic is analysed by determining ferroelectric polarization based on the calculation of the Berry phase. The theoretical results obtained are consistent with the experimental reports, which is why the Eu2Bi2Fe4O12 material is expected to exhibit biferroic behavior at low temperatures, because the Berry phase introduces hybridizations between the 3d-Fe and 2p-O states that favor the occurrence of Dzyaloshinskii-Moriya interactions, which facilitate the occurrence of ferroelectricity coexisting with weak ferromagnetism. An extensive study of the thermodynamic properties in the presence and absence of the Berry phase is undertaken by means of the Debye quasi harmonic model. The specific heat difference with and without the Berry phase reveals the occurrence of a ferroelectric transition at T = 113 K without the application of external pressure. When the applied pressure is incremented, a systematic increase in the transition temperature is observed due to the reduction of overlap between the 3d-Fe orbitals and the 2p-O orbitals in the compressed octahedra of perovskite.

A First-Principles Study of Structure, Elastic and Electronic Properties of GeTiO3 as Environmentally Innocuous Ferroelectric Perovskites

The structural parameters, elastic properties, spontaneous polarization, electronic band structure, and density of states (DOS) of GeTiO3 in tetragonal phase have been studied computationally using pseudopotential plane-wave (PP-PW) method based on the density functional theory (DFT). The generalized gradient approximation (GGA) was used to estimate the exchange-correlation energies. The equilibrium lattice parameter, unit cell volume, bulk modulus and its derivative are obtained and compared with the available theoretical data. The elastic characteristics such as elastic constants, Poisson’s ratio, elastic modulus, and anisotropy factor are obtained in the pressure range 0–50 GPa. Our computed results of elastic constant satisfy Born’s stability criterion. In view of Pugh’s prediction standard, the material is taken as ductile. Once the elastic constant is calculated, the Debye temperature of GeTiO3 compound is also evaluated from the average sound velocity. The density of states, band structures, and charge-density distribution are discussed and compared with previous computational results. The calculation within Berry’s phase approach indicate a high spontaneous polarization of tetragonal GeTiO3 (1.125 C/m2). Thus, the substance is identifi ed as a promising environmentally friendly ferroelectric material.

Effect of Doping on the Photoelectric Properties of Borophene

Borophene is a new type of two-dimensional material with a series of unique and diversified properties. However, most of the research is still in its infancy and has not been studied in depth. Especially in the field of semiconductor optoelectronics, there is no related research on the modulation of photoelectric properties of borophene. In this work, we focus on the effect of doping on the photoelectric properties of borophene by using the first-principles pseudopotential plane wave method. We calculate the geometric structure, electronic structure, Mulliken population analysis, and optical properties of impurity (X = Al, Ga) doped α-sheet borophene. The results show that α-sheet borophene is an indirect band gap semiconductor with 1.396 eV. The band gap becomes wider after Al and Ga doping, and the band gap values are 1.437 eV and 1.422 eV, respectively. Due to the orbital hybridization between a small number of Al-3p electrons and Ga-4p state electrons and a large number of B 2p state electrons near the Fermi level, the band gap of borophene changes and the peak value of the electron density of states reduces after doping. Mulliken population analysis shows that the B0-B bond is mainly covalent bond, but there is also a small amount of ionic bond. However, when the impurity X is doped, the charge transfer between X and B atoms increases significantly, and the population of the corresponding X-B bonds decreases, indicating that the covalent bond strength of the chemical bonds in the doped system is weakened, and the chemical bonds have significant directionality. The calculation of optical properties shows that the static dielectric constant of the borophene material increases, and the appearance of a new dielectric peak indicates that the doping of Al and Ga can enhance the ability of borophene to store electromagnetic energy. After doping, the peak reflectivity decreases and the static refractive index n0 increases, which also fills the gap in the absorption of red light and infrared light by borophene materials. The research results provide a basis for the development of borophene materials in the field of infrared detection devices. The above results indicate that doping can modulate the photoelectric properties of α-sheet borophene.