Quantum Espresso Package Research Articles

Ab initio study of the adsorption of SO2 on single-atom Cu-decorated ZnO(0001) surface.

The World Health Organization has cataloged sulfur dioxide (SO2) as harmful for the human health and the environment. It also contributes to generate acid rain, which affects the ecosystems. To reduce its negative effects, new strategies to control the emissions are required. New and engineered materials are investigated to detect, capture, and eradicate toxic gases from the environment. Zinc oxide is considered a promising candidate. Here, we investigate the Cu-decorated ZnO(0001) surfaces as a single-atom catalyst (SAC) to reduce SO2 by first-principles calculations. We propose a two-step reduction mechanism. First, one of the S-O bonds is broken on the pristine surface, with a calculated activation energy of 14.76kcal/mol, 1.84kcal/mol larger than the one obtained in the Cu SAC. In the second step, the SO reduction is viable only for Cu SAC, with calculated activation energy of 29.28kcal/mol. Our results point that Cu SAC improves the SO2 reduction, pointing it as a potentially efficient device to eradicate such harmful pollutant from the environment. The calculations were performed using the density functional theory, as implemented in quantum ESPRESSO package. The exchange-correlation energy was calculated within the generalized gradient approximation with the Perdew-Burke-Ernzerhof parameterization. Van der Waals dispersion-corrected interactions were considered. Spin-polarization was considered for studying dangling bonds in transition states. The minimum energy pathways were calculated by using the climbing image nudged elastic band.

First-principles study on crystal structures and bulk modulus of CuInX2 (X = S, Se, S-Se) solar cell absorber

Chalcopyrite semiconductors are widely used as absorbers in thin film solar cells, especially flexible solar cells, due to their high power conversion efficiency. They also have interesting mechanical properties, making them promising materials for flexible, light, and thin solar cells. In this work, we report the first-principle calculations of the lattice constant and bulk modulus for CuInS2, CuInSe2, and CuIn(S,Se)2 absorber solar materials. All calculations are performed using plane wave as implemented in the Quantum ESPRESSO software package in the framework of density functional theory using PBE-GGA approximations and ultrasoft pseudopotentials. The calculated lattice constant correlates well with the available experimental study. The energy-volume and pressure-volume relations are described using the third order of Birch-Murnaghan’s equation of state to calculate the bulk modulus of the absorber solar material, which is associated to the hardness of a material under particular conditions. The values of bulk modulus obtained for CuInS2 and CuInSe2 are in good agreement with available theoretical results, except for CuIn(S,Se)2, which have been calculated and reported for the first time.

Ab-initio probe into the elastic, mechanical and thermo-mechanical properties of CsSe binary compound

First principles computational simulations were performed using Quantum ESPRESSO package within the framework of Density Functional Theory (DFT) in order to analyze the structural, elastic and thermo-mechanical conditions of one of the Caesium monochalcogenides (CsSe) in a bid to fill some of the theoretical information gaps in this material. The obtained optimized lattice parameter of 7.432[Formula: see text]Å from well convergence tests agreed reasonably with results from other previous theoretical works. Three independent elastic constants ([Formula: see text], [Formula: see text] and [Formula: see text]) and other mechanical indices for this cubic system were determined by fitting stress–stain relationship data via Voigt–Reuss–Hill approximation (VRHA) of Quantum ESPRESSO incorporated Thermo_pw code. CsSe is elastically and mechanically stable since the elastic constants fulfilled the Born–Huang cubic mechanical stability criteria of forms: [Formula: see text]; [Formula: see text] and [Formula: see text]. The resistiveness of CsSe to recoverable deformation under applied force was studied via elastic moduli: bulk (B), Young (E) and shear (G) moduli. Pugh’s ratio ([Formula: see text]) [Formula: see text] depicted ductility and the positive value of Cauchy pressure: [Formula: see text][Formula: see text]GPa further confirmed the ductile nature of this system. Poisson ratio, [Formula: see text], within the domain of 0.25 and 0.42, classified the compound as a metallic bonded specie. One of the three estimated sound velocity variants for the system best predicted the average Debye temperature. Some other important structural and thermo-mechanical-related parameters such as Zener anisotropy, elastic constants based Debye temperature, average speed of sound, Lame’s constants, Kleinmann parameters, hardness (micro and macro) and melting temperature were determined. The interdependencies of these obtained parameters were established and reported.

First-principles Study on the Structural, Electronic, and Elastic Properties of Transition Metal Dichalcogenides

In this paper, the structural, electronic, and elastic properties of molybdenum disulfide (MoS2) in hexagonal and trigonal phases were investigated using first-principles calculations based on density functional theory (DFT) as implemented in the Quantum ESPRESSO package. Our findings from the structural and electronic properties of MoS2 show that bulk hexagonal and trigonal MoS2 phases have a calculated bandgap of 1.37 and 1.56 eV respectively, which is in good agreement with available theoretical and experimental results. The elastic properties show that both space groups of MoS2 are brittle at zero pressure and they also agree with Born's mechanical stability condition. The overall results place our new optimized MoS2 as a potential candidate for optoelectronic application.

First principle study on the Structural and Electronic Properties of Lead-Free Double Halide Perovskite Cs2InSbCl6

The structural and electronic characteristics of Cs2InSbCl6 were investigated using first principle density functional theory (DFT) within local density approximation (LDA) and generalized gradient approximation (GGA) as implemented in the Quantum ESPRESSO package. A supercell with 40 atoms was used in carrying out the calculations, using the optimized lattice parameters of the Cs2InSbCl6 (a = b = c =11.342 Ǻ). The findings revealed that Cs2InSbCl6 is a direct band gap material with gaps of 0.74 eV and 0.99 eV for LDA/PZ and GGA/PBE respectively, in which the GGA/PBE gap shows consistency within the literature range. The calculated densities of states highlight the contributions of the constituent atoms within the valence and the conduction bands.

Electronic and magnetic properties of Half Heusler alloy NiCrSi

Utilizing the Quantum Espresso Package and the plane wave pseudopotential approach, the electrical and magnetic characteristics of the Half Heusler alloy NiCrSi have been investigated.Ultrasoft pseudo-potential is used for this calculation. Through our calculation, it was revealed that NiCrSi is a half-metallic ferromagnet in nature with a bandgap of 0.81eV and an effective moment of 2µB respectively. The origin of the gap is mainly due to the covalent band gap and d-d band gap in the system separating bonding states from anti-bonding states. Our calculation predicts a larger spin moment at Cr site than at Ni site which is antiparallel to the moment of Si. The hybridization of Ni- 3d and Cr-4d states can open a minority spin gap at Ef resulting in the semi-conducting nature of the minority spin band.

Effects of Nickel/Manganese Variation on Na2Mn3–zNizO7 for Sodium-Ion Battery Cathodes

This paper discusses the process of determining the energy density and electronic properties of sodium-ion batteries with nickel doping and the manganese–oxygen combination (Na2Mn3–zNizO7) using the density-functional theory calculation in Quantum Espresso software. These materials were chosen due to their abundance in nature as an alternative to overcome the limitations of lithium materials. Moreover, Na2Mn3–zNizO7 has a similar structure to lithium-based batteries that have been widely used. The Na transfer process and activation energy were simulated, and the voltage and the electronic properties of the material were analyzed using first-principles calculation. This research shows that the material (Na2Mn3–zNizO7) has the potential to be implemented as a cathode material in secondary batteries.

Elucidating the Structural, Electronic, Elastic, and Optical Properties of Bulk and Monolayer MoS2 Transition-Metal Dichalcogenides: A DFT Approach.

Due to their outstanding properties for optoelectronic and versatile electronic applications, the atomically thin layers of transition-metal dichalcogenide (TMDC) materials have demonstrated a potential candidacy to succeed its analog silicon-based technology. Hence, the elucidation of the most important features of these materials is indispensable. In this study, we provide a theoretical elucidation of the structural, electronic, elastic, and optical characteristics of TMDCs. The study has been carried out by elucidating the material in its two particular forms, namely, bulk and two-dimensional (2D) layered (monolayer). The theoretical investigation was carried out within the framework of the density functional theory (DFT) method using first-principles calculations. The Perdew-Burke-Ernzerhof (PBE) variant of the generalized gradient approximation (GGA) scheme, as performed in the Quantum Espresso package, is used. Van der Waals density functional effects, involving the nonlocal correlation part from the rVV10 and vdW-DF2 methods, were treated to remedy the lack of the long-range vdW interaction. An illustration of the performance of both rVV10 and vdW-DF2 functionalities, with the popular PBE correlations, is elucidated. The Born stability criterion is employed to assess structural stability. The obtained results reveal an excellent stability of both systems. Furthermore, the theoretical results show that band-gap energy is in excellent agreement with experimental and theoretical data. Pugh's rule suggested that both the bulk and MoS2-2D layered systems are ductile materials. The refractive indices obtained herein are in good agreement with the available theoretical data. Moreover, the theoretical results obtained with the present approach demonstrate the ductility of both systems, namely, the bulk and the MoS2-2D layered. The results obtained herein hold promise for structural, elastic, and optical properties and pave the way for potential applications in electronic and optoelectronic devices.

Cellmetry: A first‐principle pKa determination by plane‐wave functions

AbstractWe developed a methodology to analyze and determine acid dissociation pKa values by using plane wave functions and density functional theory. The periodicity of the PW functions allows us to scan the energies as well as the derived pK values. Explicit and implicit solvent effects were also taken into account to study the pK tendencies along the cell sizes. Some well‐known molecules (water, ammonia, alcohols, peroxides, phenol, amines, and N‐heterocyclic compounds) were studied which covered a wide range of structural/electronic properties to analyze the accuracy and the limit of the methodology. Some motifs were found by scanning the cell size‐dependent pK values which belong to the cell size range where the experimental pK value or range can be found. Several strategies were carried out which can do good or even excellent (±0.3) predictions for other compounds based on our study. Our detailed computational “titration” was made by the Quantum Espresso software package.

Density functional theory study of different metal dopants influence on the structural and electronic properties of a tetragonal α-PbO

In this work, using the Quantum ESPRESSO package, density functional theory was used to study the effects of different metal dopants on the structural and electronic properties of tetragonal α-PbO. Tetragonal α-PbO has attracted attention due to its application in various optoelectronic devices. However, in order to apply it in these technologies suitably, its properties have to be improved since it has low electronic conductivity. In this study, nine different metals from alkali metals, p-block metals, and 3d-transition metals have been used as dopants to investigate its electronic properties. Moreover, the performance of four pseudopotentials was tested. Via the partial density of state and band structure calculations, an indirect bandgap was found for pristine α-PbO. The generalized gradient approximation of the Perdew–Burke–Ernzerhof exchange correlation with ultrasoft pseudopotential gives 1.75 eV for pristine α-PbO, which decreased during the incorporation of different metal dopants. Depending on the position of the Fermi level and impurity energy level in metal doping, the n- or p-type conductivity has been identified. The calculated partial density of states shows the contribution of orbital states of dopants to the partial density of states. The valence band maximum is mainly made of O-2p states whereas the conduction band minimum is dominated by Pb-6p states in undoped α-PbO. The calculated lattice constants were a = b = 3.997 Å and c = 5.220 Å, which are in best agreement with the experimental values. The computational study verified that doping various metals had a significant effect on the structural and electronic properties of α-PbO.

First principles calculation to investigate the structural, electronic, elastic, mechanical, and optical properties of K2NiP2 ternary compound

First-principles calculations of the structural, electronic, elastic, mechanical, and optical properties of the K2NiP2 ternary compound using density functional theory as implemented in the quantum espresso package have been performed. The calculations have been done using the generalized gradient approximation (GGA) with the Perdew–Burke–Ernzerhof (PBE, PBEsol) exchange-correlation functionals and the local density approximation (LDA). The lattice parameters have been found to agree with the available experimental results. Direct bandgaps have been obtained as 0.630, 0.588, and 0.525 eV when using the GGA-PBE, GGA-PBEsol, and LDA approximations, respectively. In all three scenarios, the valence bands have been noted to be majorly formed by Ni-3d and P-2p states with little contribution from the other states, whereas the conduction bands have been observed to be mainly formed by P-2p states with a small contribution from the other states. The K2NiP2 has been found to be mechanically stable, ductile, and ionic. The optical properties showed that the compound under investigation has a high refractive index and absorption coefficients covering the ultraviolet–visible regions, thus indicating its potential for photovoltaic applications. The bandgaps obtained using LDA were smaller than those obtained using GGA. This is because LDA underestimates the bandgaps.

Experimental and First-Principles Thermoelectric studies of Bulk ZnO

The Thermoelectric perspective to produce electricity from waste heat has obtained great attention over the last few years. However, the fulfillment of energy requirement of the contemporary world by the thermoelectric method can be achieved by developing good thermoelectric materials of high conversion efficiency. Density functional theory (DFT) is widely used simulation technique in the materials science field for computing electronic properties of the materials. In our DFT calculation Quantum Espresso (QE) package were used to investigate the electronic band structure as well as electronic density of states of bulk ZnO sample. To express core electrons, projector-augmented wave (PAW) pseudopotentials were chosen and to optimize band structure LDA+U method of DFT approximation was opted. Our DFT calculations give direct band gap 3.2004 eV and the experimental value is 3.24 eV. Our works are found to be good acceptance with previously reported values and the DFT study via QE and BoltzTraP codes are suitable for predicting the thermoelectric properties of semiconductor materials.

A DFT study of structural and electronic properties of cubic thallium based fluoroperovskites TlBF3 (B[dbnd]Ge,Sn,Pb,Zn,Cd,Hg,Mg,Ca,Sr,Ba)

This study aims to use Density Functional Theory (DFT) to investigate structural and electronic properties of cubic fluoroperovskites TlBF3 (B = Ge, Sn, Pb, Zn, Cd, Hg, Mg, Ca, Sr, and Ba). The calculation was performed using the Quantum Espresso package using GGA-PBE functional. The optimized lattice parameters for the perovskites ranged from 4.01 Å to 5.08 Å while direct and indirect band gaps were observed, with band gaps between 0.75 eV and 4.48 eV. Results were in good agreement with other theoretical studies using different functionals and packages. It was also found that for all compounds analyzed separately based on three different columns of the periodic table, the larger the atomic radii of the B cations, the larger their equilibrium lattice constants. In addition, an increase in the electronegativity of cations leads to a decrease in covalent character of B–F bonds while Tl–F bond is mainly ionic for all compounds.

A DFT study of gas molecules adsorption on intrinsic and Cu-doped graphene gas nanosensors

In this study, first-principles calculations are performed to investigate the sensitivity of intrinsic graphene sheet (GS) and Cu-doped graphene sheet (Cu-GS) gas nanosensors for adsorbing CO, H2, and H2S gas molecules using QUANTUM ESPRESSO package. The density of states (DOS), net charge transfer, adsorption energy, partial density of states (PDOS), and the most stable adsorption configuration of these molecules on GS and Cu-GS are studied. The results show the weak physical adsorption of the three gas molecules on GS. The strength of interaction between the Cu-GS system and adsorbed gas molecules is higher due to the Cu doping. It is expected that the significant increase in charge transfer and adsorption energy leads to fundamental improvement in the electrical conductivity of the Cu-GS system. The results indicate that the introduction of Cu impurity can improve the gas sensing properties of graphene-based gas nanosensors. Therefore, Cu-GS is more appropriate for detecting gas molecules compared to pure GS. The results in this study are useful for developing the design of gas nanosensors.

Density functional theory investigation on structural, mechanical, electronic and vibrational properties of Heusler alloys AlXIr2 (X = Co, Cr, Cu, Fe and Zn)

This study focuses on the detailed investigation of full-Heusler AlXIr2 (X = Co, Cr, Cu, Fe and Zn) alloys. A first-principal plane-wave pseudopotential method based on density functional theory is adopted. The quantum-espresso package combined with the generalized gradient approach is used to reveal the structural, electronic, magnetic, mechanical and lattice dynamic properties of full-Heusler AlXIr2 (X = Co, Cr, Cu, Fe and Zn) alloys. The elastic constants are used to determine elastic stabilities of alloys based on Born criteria. The analysis showed that all alloys are elastically stable. Further detailed analysis has been carried out to reveal mechanical properties. It is found that all alloys are ductile and anisotropic. The electronic band structures are also obtained. All alloys except for AlCrIr2 are found to be metallic. AlCrIr2 has half-metallic nature. In addition, AlCrIr2, AlFeIr2 and AlCoIr2 has shown magnetic properties. The phonon spectra and density of states are investigated to examine dynamical stability. It is seen that all alloys exhibit dynamical stability due to having positive phonon frequencies.

Synchrotron EXAFS spectroscopy and density functional theory studies of Pd/MoS2 Schottky-type nano/hetero-junctions

Molybdenum disulfide (MoS2) nanostructures are grown on the silicon substrates using thermal chemical vapor deposition and then Pd anchoring on them is carried out by DC magnetron sputtering to form Pd/MoS2 Schottky-type nano/hetero-junctions. Extended X-ray absorption fine structure (EXAFS) spectroscopy is applied to study the local structure around the molybdenum K-edge. In this way, the kind, coordination number, and distance of neighbors of absorber atom are determined. Moreover, structural analysis has been performed by X-ray diffraction. Optical studies are conducted by UV–Visible and differential reflectance spectroscopy. The electronic properties of the samples are examined using Raman spectroscopy with an excitation laser at 532 nm. Furthermore, the surface chemical analysis is monitored by X-ray photoelectronspectroscopy. In addition, a simulation study of the structural and electronical properties of the samples is carried out to understand the effect of Pd adding on MoS2 structure using Quantum ESPRESSO software. The reasonable place of the Pd atom after Pd anchoring in MoS2 lattice is obtained.

The influence of surface Fe on the corrosion of Mg

Iron is a common impurity in magnesium alloys, and is acknowledged to accelerate Mg corrosion, contributing to Mg’s poor corrosion resistance. However, an atomistic understanding of this acceleration effect is still incomplete. Here we use Density Functional Theory simulations performed with the Quantum Espresso package to investigate several Fe/Mg models, calculating the associated work functions, atomic charges, and H and Fe absorption energies. Compared with a pure Mg slab, we find that Fe’s existence increases the work function and decreases the H adsorption energy. Furthermore, a general trend is observed that the Fe absorption energy decreases with increasing interaction between Fe atoms on the Mg substrate. Based on these results, a mechanism based on charge redistribution is put forward to explain how Fe accelerates the corrosion of Mg. Our findings provide insight into Mg’s corrosion process at the atomic level that might inform future measures to prevent corrosion.

Impact of compositional disorder on electron migration in lutetium–yttrium oxyorthosilicate scintillator

A general description of the dynamics of nonequilibrium carriers in multicomponent activated scintillation materials with a compositional disorder of the crystalline matrix is developed and applied for studying the excitation transfer and timing properties of lutetium–yttrium oxyorthosilicate (LYSO). The energy structure, the density of states, and the effective potential of LSO and YSO crystals have been calculated by using the Quantum Espresso package. An analytical form of the potential fluctuations due to compositional disorder is suggested in the pseudopotential approximation. The spatial distribution of lutetium and yttrium cations in the LYSO crystal has been simulated by the Monte Carlo method using the thermodynamic approach for three qualitatively different cases of cation distribution: uniform, heterogeneous neighboring, and clustered. The impact of the compositional disorder on electron migration is found to be qualitatively different in four typical regions of electron energy. The density of localized states in LYSO calculated using the coherent potential approximation (CPA) and the quasiclassical approach is comparable to the density of secondary carriers expected in an ionization track and might have significant influence on the migration of thermalized carriers. The transport mean free path of nonlocalized electrons limited by elastic scattering on pseudopotential fluctuations is shown to be substantially longer than that due to longitudinal optical phonon emission in the low-energy region (calculated using CPA) and the high-energy region (calculated using the Born approximation). The scattering on pseudopotential fluctuations is important for intermediate-energy electrons due to a substantial influence of the core potential fluctuations on high-energy branches.

Ab initio investigation of electronic and optical properties of three quaternary types: CuMn2InSe4, CuMn2InTe4 and CuNi2InTe4

Regarding the significant rule of quaternary type semiconductors in nanoscience and industry, we have investigated the electronic and optical properties of CuMn2InSe4, CuMn2InTe4 and CuNi2InTe4 using quantum espresso package. To this end, band structure and density of states has been studied. Imaginary and real part of electrical permittivity has been investigated and discussed about their features. The band gap of spin down band structure for CuMn2InTe4 has been detected approximately 1 eV and the band gap of CuNi2InTe4 is 1.2 eV belong to spin up. Also, CuMn2InTe4 has a band gap of 0.6 eV for Spin-Down. Obtained results demonstrate that the electrical permittivity of CuMn2InSe4 and CuNi2InTe4 has a positive amount in zero energy. In addition, by increasing energy the electrical permittivity has been declined until reach to a minimum in negative range, then come back to zero. However, it has a negative amount in zero energy for CuMn2InTe4, and first increases with growing of energy then decreases until reach to zero. The obtained results and findings of this research for electronic and optical properties of CuMn2InSe4, CuNi2InTe4 and CuMn2InTe4 are in close match with the theoretical and experimental data, in terms of trend and value.

Tuning the HOMO and LUMO energy levels of dye sensitizers with electron-accepting capability and electron-drawing capability of substituents to optimize the efficiency of dye-sensitized solar cells: Approach of theoretical

In this work, for first time, TiO2 nanoparticles (TiO2 NPs) was synthesized by Dodecan-1,12-bis (triethylammoniumbromide) bolaform surfactant as template with sol-gel method. Then, prepared TiO2 NPs was crystalized in anatase phase and properties of this TiO2 NPs were compared with the properties of commercial TiO2 (P25). BET result demonstrated that compare to P25, synthesized TiO2 NPs has a very higher surface area. Both TiO2 were sensitized with N719 dye and then they used as photoanode to compare their results. The results displayed that although synthesized TiO2 NPs has lower efficiency in solar cell, it has a better fill factor compared to the P25. Also, the properties of TiO2 NPs in anatase phase in bulk and at (1 0 1) surface have been investigated by using quantum espresso (QE) package. The Band Structure and density of State (DOS) TiO2 NPs in bulk and at (1 0 1) surface have been studied. What is interesting in this article is that Dodecan-1,12-bis (triethylammoniumbromide) bolaform surfactant has been used as a templet by sol-gel method, which has increased the level of synthesized TiO2, resulting in the absorption of pigment on TiO2 increases. Absorption of more pigment on TiO2 can reduce dark stream recombination.