Plane-wave Self-consistent Field Research Articles

First-principles calculations to investigate the elastic, electronic, dynamical, and optical properties of cubic ZrCoAs half-Heusler semiconductor for photovoltaic applications

The electronic, mechanical, elastic, dynamical, and optical properties of the ZrCoAs half-Heusler compound have been systematically investigated using the plane wave self-consistent field approach with the Perdew-Burke-Erzerhof generalized gradient approximation (GGA-PBE) exchange-correlation functional. The study includes examinations with and without spin orbit coupling (SOC) effects. Results indicate a decrease in the Kohn-Sham band gap with the inclusion of SOC effects. Electronic bandgap formation was attributed to Co 3d, Zr 3d, and As 2p for the conduction band, and Co 3d and As 2p for the valence band without SOC effects. With SOC, Co 5d, Zr 8d, and As 3p dominated the conduction band, while Co 3d and As 3p dominated the valence band. The lattice constant showed a 0. 063% decrease with the SOC effects, which is better aligned with the experimental observations. ZrCoAs demonstrated ductility, mechanical stability, and dynamical stability. The optical properties were found to be excellent for photovoltaic applications, suggesting its potential in solar energy conversion technology. This study provides valuable information on ZrCoAs and presents opportunities for its use in solar cells, optoelectronic devices, and thermoelectric applications. The material's versatility and suitability for practical applications make it a promising candidate for further exploration in renewable energy research.

Tuning the magnetic properties of doped ZnS using transition metal doping: A multi-scale computational approach

Transition metal (TM)-doped dilute magnetic semiconductors (DMS) have emerged as promising materials for spintronic applications such as spin-polarized transport and information storage. However, achieving robust room-temperature ferromagnetism in DMS remains a key challenge. This work undertakes a comprehensive investigation of the effects of Ti- and Cr-doping and (Ti,Cr)-codoping on the structural, electronic, and magnetic properties of wurtzite ZnS using first-principles pseudopotential plane-wave self-consistent field calculations and Monte Carlo simulations. The first-principles DFT calculations were performed using the spin-polarized GGA+U approach to account for strong electron–electron interactions. Structural relaxations revealed expanded lattice parameters and bond lengths for the doped systems compared to pure ZnS, attributed to the larger ionic radii of the dopants. Formation energy calculations confirmed the thermodynamic stability of doping. The band structure and density of states analysis demonstrated the half-metallic nature of the doped ZnS systems with 100% spin polarization induced by strong hybridization between the TM-3d and S-3p states. This mediates robust ferromagnetic coupling, with total magnetic moments around 4-8 μB/cell depending on dopant type and concentration. To complement the zero-temperature DFT results, temperature-dependent Monte Carlo simulations using the single-spin flip Heat Bath algorithm were implemented. The modeling of magnetization, susceptibility, specific heat, and hysteresis loops enabled extracting Curie temperatures up to 427.6 K for 12.5% Cr-doped ZnS. The synergistic combination of first-principles DFT and Monte Carlo computational techniques provides significant insights into tailoring the magnetic properties of TM-doped ZnS dilute magnetic semiconductors. The tunability of structural, electronic, and magnetic characteristics through control of dopant selection and concentration demonstrates the promising potential of transition metal-doped ZnS for spintronic devices operable at room-temperature.

Density Functional Theory Computation of the Electronic, Elastic, Phonon, X-ray Spectroscopy, and the Optoelectronic Properties of CsXI3(X: Si, Ge, Sn) Halide Perovskite Materials

Perovskites are a promising candidate for various applications including solar cells, light-emitting diodes, photodetectors, and photocatalyst owing to their exceptional properties. However, their long-term stability remains a critical challenge that hinders their widespread use. In this study, we explore key stability factors pertaining to perovskites by examining the structural, mechanical, phonon, thermodynamic, X-ray and optoelectronic properties of CsXI3 (X: Si, Ge, Sn) using density functional theory (DFT) method, employing the plane wave self-consistent field (PWscf) code embedded in the Quantum Espresso Simulation Package (QESP). From the results, the investigated materials show a tolerance factor of 0.9846, 1.1096, and 0.9982, and octahedral factor of 0.4223, 0.2621, and 0.4029 for CsGeI3, CsSiI3, and CsSnI3, respectively. It was further discovered that the bulk modulus of each crystal dependent on the boiling point of the[Formula: see text] cation in CsXI3 were the values obtained, which are 7.86, 19.23, and 22.72 corresponding to CsGeI3, CsSiI3, and CsSnI3, respectively. The band structure results clearly indicate a substantial overlap between the valence band and the conduction band of CsXI3 (X: Si, Ge, Sn), resulting in a complete absence of a bandgap. This observation strongly suggests that the perovskite compound exhibits metallic properties. This study demonstrates a novel method for obtaining stable perovskites of cesium halide suitable for applications in solid-state electronics.

CO to formaldehyde transformation study on pristine and Au-modified BaTiO3(001) through DFT calculations.

BaTiO3 is one of the most important ferroelectric oxides in electronic applications. Also, it has attractive properties for catalysis that could be used for reducing contamination levels, especially carbon monoxide, CO. CO is one of the main gaseous pollutants generally released from the combustion of fossil fuel. In this work, the CO transformation on pristine and Au-modified BaTiO3 perovskite for H2CO obtention is studied. The CO adsorption and hydrogenation on pristine BaTiO3 leads to formaldehyde synthesis as the most stable product through two possible routes. Furthermore, hydrogenation stages are less probable on pristine BaTiO3. On Au-modified BaTiO3 formaldehyde is the principal product too but Au adatom generates H2CO competition with HCOH. After BaTiO3 modification with Au unpaired electrons were generated. These unpaired electrons are related to the adatom reactivity. According to the obtained results, pristine and Au-modified BaTiO3 can adsorb and hydrogenate CO generating formaldehyde as the principal product. BaTiO3 modifications with Au increase the reactivity of the perovskite in the CO hydrogenation reactions. CO hydrogenation process on Au suggests that further hydrogenation stages beyond formaldehyde are possible. The study was performed through ab initio calculations using the periodic spin-polarized Density Functional Theory (DFT) as implemented in Quantum ESPRESSO. DFT calculations were carried out using the Plane Wave self-consistent field (PWscf). Spin density difference allows us to identify reactive regions related to dangling bonds and unpaired electrons. A plane wave basis set was used to represent the electron states. Vanderbilt pseudopotentials with nonlinear core correction were used to model the ionic cores and valence electrons interaction. Exchange-correlation energies were treated within the generalized gradient approximation (GGA) with the Perdew-Burke-Ernzerhof (PBE) parameterization.

Ab-initio investigation of the fundamental properties of metals (X = Be, Mg, and Ca) encapsulated CsXO3 tin-based perovskite materials

Perovskite material are widely used in Solar cell device due to it promising properties and power conversion efficiencies (PCE). Most importantly, properties of the absorber layer such as the band gap, electronic, optical, chemical composition and the grain size of the perovskite absorbed layer are very sacrosanct when determining efficacy of the material for such application. Thus, in this work, the optical, structural stability, electronic, and mechanical properties of non-halide cubic perovskite CsXO3 (X = Mg, Be and Ca) was extensively studied using the first principles Density functional theory (DFT) approach. The structural, electronic and optoelectronic properties was evaluated using Quantum Espresso Simulation Package (QESP) with the plane wave self-consistent field (PWscf) code. The structural computation reveals that the Lattice constant as well as total energy of CsXO3 (X = Be, Mg and Ca) increases as the size of cation X (X = Be, Mg and Ca) increases such that CsCaO3 possess the highest energy. Contrary, the fermi energy decreases with increase in cationic size, however, CsCaO3 has the highest lattice constant value 4.3743 eV. Electronic properties investigation shows that the studied perovskite has a metallic property with no forbidden band. zero band gap materials can adsorb photon across the entire solar spectrum, including lower-energy photons which is an advantage over a non-zero band gap which can only absorb photon with energies higher than the band gap energy can be absorbed and converted into electricity. This enables more efficient utilization of sunlight and increased overall energy conversion. To ascertain the effect of atomic exchange and orbital contribution in the formation of electronic properties, partial density of state (PDOS) was calculated and the result reveal that electron transition occurs mostly from p-orbital oxygen atom having major contribution on the valence band to the d-orbital of Caesium atom having major contribution on the conduction band and X-cation having minor contribution. CsXO3 (X = Be, Mg and Ca) also shows fascinating optical properties and thus can be used to improve solar cell device.

Study of structural, magnetic and electronic properties of a new off-stoichiometric series of full-Heusler alloy Co2Nb1+xZ1−x (Z = Sn, In, Ga): Ab initio approach

Using ab initio calculation, we investigate systematically the structural, electronic and magnetic properties of Co2Nb1+xZ1−x (x = 0, 0.25, 0.50). Here, Plane-Wave self-consistent field (PWscf) program implemented in open-source Quantum Espresso software package within generalized gradient approximation (GGA) - Perdew-Burke-Ernzerhof (PBE) for the exchange-correlation functional has been used. Equilibrium lattice parameters in cubic austenitic phase of Co2Nb1+xZ1−x (x = 0, 0.25, 0.50) have been inquired. It has been found out that except Co2NbSn, all the compositions do not show martensitic structural transition. The microscopic origin for this has been associated with Jahn-Teller distortion of Co 3deg orbitals in close proximity of the Fermi level. The density of states for both tetragonal and 4 O orthorhombic structure in martensitic phase of Co2NbSn have been investigated. Moreover, from the density of states plots we have recognized the metallic character of Co2NbSn. However, Co2NbGa & Co2NbIn and all of the off-stoichiometric alloys have been anticipated to possess partial half-metallic character. Furthermore, we have examined the total magnetic moment and average atomic magnetic moments in off-stoichiometric Co2Nb1+xZ1−x in the cubic phase to understand the effect of Nb doping in stoichiometric compounds. Nb doping increases the total magnetic moment due to increased Nb-Co hybridization of d orbitals.

A DFT study of electronic and thermoelectric properties of arsenic doped graphene

This study mainly focuses on the electronic and thermoelectric properties of arsenic (As) doped monolayer graphene, Gr7As. Calculations were done using Density Functional Theory. Plane-Wave Self-Consistent Field (PWscf) code of the Quantum Espresso is used for the calculations. A 2x2x1 graphene supercell is used. Electronic properties of pristine and arsenic doped monolayer graphene are examined by First Principle Study. BoltzTraP package is used for the calculation of thermoelectric properties of arsenic doped monolayer graphene. The addition of foreign atoms into pure graphene provides a possibility for band opening. By band opening, several properties of graphene can be changed depending upon the type of dopant and its concentration. Here, in this study, we investigate the properties of graphene doped by 4p dopant for various applications. We show that by adding 4p dopant like arsenic in the pristine graphene, the behaviour changes from semi-metallic to metallic and there is a significant increase in the value of the Seebeck coefficient and figure of merit.

First-Principles Study of Carrier-Mediated and Vacancy-Induced Ferromagnetism in Molybdenum Disulfide Monolayer

We have investigated the magnetic properties of semiconducting molybdenum disulfide (MoS2) monolayer (ML) using the plane wave self-consistent field (PWscf) method within the framework of density functional theory (DFT). The pristine semiconducting bulk MoS2 is nonmagnetic (NM), due to the spin pairing of two electrons. We have indicated that the carrier-mediated ferromagnetism is available on the MoS2 ML as both the hole and electron carriers. The ordinary neutral S (VS0) vacancy creates the localized vacancy defect level and this level does not create the ferromagnetic (FM) state due to the spin pairing of two electrons by three Mo dangling bonds. While we have shown that the FM state is possible to create the FM state, due to the additional hole and electron carriers on the valency band and localized vacancy defect level by positively and negatively charged S (VS1+ and VS1- ) and positively charged Mo (VMo1+) vacancies.

The Enhancement of Selectivity and Activity for Two-Electron Oxygen Reduction Reaction by Tuned Oxygen Defects on Amorphous Hydroxide Catalysts

Amorphous catalysts, thanks to their unique coordinately unsaturated properties and abundant of defect sites, incline to possess higher activity and selectivity than their crystalline counterparts....

Size and strain induced phase formation and ferromagnetism in reduced TiO2 powders

We investigate the strain evolution, phase formation and ferromagnetism of nanocrystalline TiO2 powders prepared by high energy planetary ball milling technique. Pure TiO2 shows the anatase phases in the structural analysis and more than 0.25 h of milled powder turns into Rutile and Magneli phases. The crystallite size and strain were calculated from the X-ray diffraction pattern using the Williamson-Hall equation and the uniform deformation energy density model. Pure TiO2 exhibits paramagnetic nature, which transforms into ferromagnetic one with a moderate moment 0.15 emu/g for 60 h milled powders at an applied field of 12 kOe. The Micro-Raman analyses show the presence of Magneli phase (Ti3O5) along with a shift in the active Eg(1) band for milled powders. X-ray photoelectron spectroscopy results show an oxygen-deficiency peak at 457.7 eV in milled powders. The electron paramagnetic resonance study shows the evidence of oxygen-deficiency which is clear from the resonance signal at 338 mT in milled powders. Further, the electronic structures are investigated by the spin-polarized plane-wave self-consistent field calculation based on density functional theory (DFT) with generalized gradient approximation (GGA) and Hubbard U corrections. The elastic properties are also calculated for pure, oxygen vacancies TiO2 and pure Magneli phase (Ti3O5) crystal. Our results demonstrate the effects of size and strain engineering on the formation of the Magneli phase due to defect induced oxygen vacancy and show the ferromagnetism in TiO2 nanoparticles, which are important for spintronics and other potential applications.

Enhanced thermodynamic properties of ZrNiH3 by substitution with transition metals (V, Ti, Fe, Mn and Cr)

First-principles calculations based on Plane-Wave Self-Consistent Field (PWSCF) method, implemented in quantum espresso program, have been performed on ZrNiH3 substituted with transition metals (V, Ti, Fe, Mn, and Cr). The study aims to investigate the heat of formation in terms of material stability and desorption temperature. It is found that the substitution by transition metals, results in a significant enhancement in the thermodynamic properties accompanied by an increase of the volumetric and gravimetric hydrogen storage capacities. In addition, the obtained values of heat of formation and desorption temperature corroborate with that required by the U.S. Department of Energy (DOE) for stability and volumetric capacity criteria. Moreover, Mn and Fe elements are found to present the lowest substituting content (34%) to obtain optimum hydrogen storage characteristics (enthalpy of formation of - 40 kJ/mol.H2, decomposition temperature of 300 K and volumetric capacity of 134 g.H2/l), without affecting the electronic structure and the metallic character of ZrNiH3.

Structural and optical properties of electrodeposited Cu2O thin films

Abstract In this work, we report on the synthesis of Cu2O thin films by electrodeposition technique. The as-electrodeposited films at −0.5 V potential for 15 min in basic solution (pH = 9) are well crystallized in cubic structure, with 〈1 1 1〉 as preferential orientation and with lattice parameter a = 4.26 A. The transmittance of Cu2O films reveals that they have high optical transmission (>70%) with direct band gap energy in order of 2.23 eV. The density functional theory using the plane-wave-self-consistent field (PWSCF) was carried out for Cu2O to determine some of their electronic properties. Theoretical analyses show that Cu2O has a direct band gap with value 2.01 eV, which is consistent with the experimental results.

Electronic-structure and thermodynamic properties of ZnS1−xSex ternary alloys from the first-principles calculations

In this paper, the composition-dependent electronic-structure and thermodynamic properties for hexagonal wurtzite (WZ) and face-centered cubic zincblende (ZB) ZnS1−xSex ternary alloys have been studied utilizing first-principles pseudopotential plane-wave self-consistent field calculations. Special quasi-random structure method was applied to generate disordered structures of 16-atom supercell for x = 0.25, 0.5 and 0.75. We obtained a direct band-gap at Г point and a shrinking tendency of the band-gap with increasing Se content in both phases. The reasons for the band-gap shrinkage have been discussed based on the analysis of electronic density of states and band offsets. Δ-sol method was applied to correct the band gaps calculated by density functional theory. The Δ-sol corrected band-gaps are in good agreement with experimental band-gaps. The thermodynamic properties were calculated by the cluster expansion method. It turns out that, the stretching forces decrease considerably and linearly with the bond length, while the bending forces are dependent insignificantly on the bond length. The phase diagrams reveal that the lattice vibration effects can influence the critical temperature Tc and the solubility of S- and Se-rich ZnS1−xSex alloys, but the influence is not obvious for ZB-ZnS1−xSex. Based on the calculated phase diagrams without lattice vibration effects, the Tc for WZ- and ZB-ZnS1−xSex are 559 K and 421 K, respectively. When the vibration enthalpy is included, the Tc values of both phases are lowered to 543 K and 418 K, respectively. And if the vibration entropy is also taken into account, the Tc values of both phases are further lowered to 529 K and 415 K, respectively. With inclusion of lattice vibration effects, the ZnS1−xSex alloy starts a phase transition from ZB to WZ at a temperature of 1600 K, and the solid solubility of Se increases with the temperature rise.

Density Functional Calculation for BP/GaN Heterostructures

Recently, it has become indispensable to use semiconducting nanostructures in the production and development of electronic devices. In this study, the bulk and nanowire heterostructures of the BP / GaN system have been investigated for the structures pure and Te atom doped. In calculations, the plane wave self-consistent field program based on density functional theory was used. The average potentials of the aforementioned systems have been calculated and the interface effect has investigated.

Ferromagnetism and half metallicity induced by oxygen vacancies in the double perovskite BaSrNiWO6: DFT study

Using the spin polarized density functional theory (DFT) and exploring the Plane-Wave Self-Consistent Field (PWscf) code implemented in Quantum-ESPRESSO package, we investigate the effect of the Oxygen vacancies (VO) and the Oxygen interstitial (Oi) on the double perovskite BaSrNiWO6. This deals with the magnetic ordering and the electronic structure in such a pure sample exhibiting the insulating anti-ferromagnetic (AFM) state. This study shows that the presence of oxygen deficient defects converts the insulating to half metal with ferromagnetic or anti-ferromagnetic states. The magnetic ordering in BaSrNiWO6−δ depends on the position of the Oxygen vacancy in the unit cell. However, it has been shown that the Oxygen interstitial preserves the anti-ferromagnetic propriety. We have computed the formation energies of different positions of the Oxygen vacancy (VO) and the Oxygen interstitial (Oi) in the BaSrNiWO6 compound. We showed that the formation of VO is easier and vice versa for the Oi formation. The obtained results reveal(VO) and the Oxygen interstitial (Oi) that the anti-ferromagnetic can be converted to ferromagnetic in the double perovskite BaSrNiWO6 induced by Oxygen vacancies VO.

Shine blue and blue-green photoluminescence in BaZrO3−δ powders: An Ab-initio analysis of structural deformation

A blue and blue-green photoluminescent emission for BaZrO3−δ powders was measured. A Plane Wave Self-Consistent Field method, based on the density functional theory and the local density approximation, was carried out to rationalize this phenomenon. The theoretical results showed that local defects in the cubic structure, caused by oxygen vacancies, play an important role in the formation of new level energy into the band gap, giving rise to the PL emission. DOS calculation showed that the new levels were linked to the d-orbital of both Ba and Zr atoms.

FIRST PRINCIPLE STUDY OF MC (M=AL, GA AND IN) AT EQUILIBRIUM AND UNDER NEGATIVE STRESS

The electronic and magnetic properties of the hypothetical compounds of MC (M=Al, Ga and In) are investigated by using first-principle calculations and pseudopotential plane wave self-consistent field method based on density functional theory. In order to find the most stable phase of MC (M=Al, Ga and In), we study them in zinc-blende (ZB), rocksalt (RS), wurtzite and NiAs crystal structures. We find that the most stable crystal structure is the RS structure by comparing the total energies of these compounds in different structures. Our calculations show that these compounds are metals in all of these structures. However, many of the nanospintronic devices are the heterojunctions of half-metals and semiconductors where the crystal structures of the layers that are grown on the semiconductors are the same as that of the semiconductors. Because most of the semiconductors have ZB structure, we investigate the electronic and magnetic properties of these compounds in this structure. It is shown that although MC (M=Al, Ga and In) compounds are metals in ZB structure, they become half-metal when relatively high negative stresses are applied over them. Therefore these compounds could be used in spintronic devices.

Structure stability analysis of Ni<SUB align="right">n(n = 2 - 22) using nature inspired algorithms: a performance study

Using nature inspired algorithms (NIAs) with plane-wave self-consistent field (PWSCF), density functional theory (DFT) and pseudo-potentials, the minimisation of potential energy and relative stability for Nin clusters (n = 2 – 22) were studied. The genetic algorithm (GA), differential evaluation (DE), particle swarm optimisation (PSO) and artificial bee colony (ABC) are used for global structural optimisations with space-fixed Cartesian coordinates. Clusters obtained from NIA search were further optimised by using first principals total energy calculations. We found that GA gives minimum energy for Nin (n = 6, 11, 16, 21), DE gives minimum energy for Nin (n = 2, 4, 7, 9, 15, 17), PSO gives minimum energy for Nin (n = 3, 10, 12, 14, 18, 20) and ABC gives minimum energy for Nin (n = 5, 8, 13, 19, 22).

Ab initio investigation of the structural and magnetic properties of Ni-Pt-Mn-Ga alloys

ABSTRACTStructural and magnetic properties of Ni2-xPtxMnGa alloys are investigated from first principles calculations with the help of the spin-polarized relativistic Korringa-Kohn-Rostoker and Plane-Wave Self-Consistent Field methods. The atomic chemical disorder at specific site has been implemented using coherent potential approximation. Calculated equilibrium lattice parameters are in a good agreement with experimental data and other theoretical calculations. The composition dependences of the magnetic exchange couplings and the Curie temperature for cubic phase are obtained. Our calculations have shown that an increase content of Pt results to decrease of magnetic interactions between Mn atoms and to change of interaction sign from ferromagnetic type to antiferromagnetic one for composition Ni1.0Pt1.0MnGa. Calculated Curie temperatures are in an agreement with experimental data.

The Structural Stabilities and Electronic Properties of Orthorhombic and Rhombohedral LaCrO<sub>3</sub> — A First-Principles Study

The equilibrium structures of orthorhombic LaCrO3 (O-LaCrO3) and rhombohedral LaCrO3 (R-LaCrO3) crystals were investigated by using the plane-wave self consistent field (PWSCF) method based on density functional theory (DFT). The optimized lattice parameters for both phases are in accordance with experimental results reported in literature, confirming the reliability of LSDA+U scheme used in the calculations. We have quantificationally investigated the binding energies and electronic properties of these two types of LaCrO3 crystals. The negative total energy and binding energies indicate the ground state property and the good structrual stability of O-LaCrO3 crystal, which is important for the preparation of nano materials, the synthesis of ceramic materials made of doped O-LaCrO3 crytals, as well as their applications in high technology fields, and predict the metastable property of R-LaCrO3 crystal. Furthermore, the band structures show that O-LaCrO3 is a direct semiconductor with wide energy gap, while R-LaCrO3 is an indirect semiconductor with narrow energy gap. The interaction between Cr and O atoms in O-LaCrO3 crystal possesses the character of covalent bonding.