Quantum Espresso Package Research Articles

Tuning the optical constants and thermal properties of CdS nanocrystals by SHI irradiation: A blended analysis through DFT+U and TS model

Here, chemically synthesized CdS nanocrystals have been irradiated with swift heavy ions (SHI) with an aim to study the changes in its optical constants such as refractive index and dielectric constant along with the bandgap modification. Scanning electron microscopy (SEM) shows spherical morphology of the pristine CdS nanocrystals with an average size of 17 nm, which gets slightly deviated from its spherical morphology after SHI irradiation. X-ray diffraction (XRD) study reveals a change in the lattice structure of CdS nanocrystals from cubic to hexagonal phase due to irradiation. Structural information obtained from the XRD data has been fed as an initial input parameter in the first principles study (DFT + U) using the Quantum Espresso package for determining refractive index, dielectric constant, band gap and thermal properties theoretically. All these theoretically obtained values of optical constants match approximately with the values obtained from the experimental UV–Visible data analysis. Finally, the value of threshold electronic energy loss has been determined from the Thermal spike model.

First-principle calculations to investigate structural, electronic and optical properties of MgHfS3

The development of a non-toxic, efficient, cheap, and emerging class of semiconductor as solar absorber is vital for photovoltaic applications. The first-principle calculation method, based on the density functional theory (DFT) and the plane-wave method as implemented in the Quantum Espresso package has been used to obtain the structural, electronic, and optical properties of MgHfS3. From analysis, the band structure shows that the material has a direct band-gap with a value of 1.43 eV, which is in close agreement with the estimates of refractive index, reflectivity and extinction coefficient. A strong optical absorption coefficient of the order of 108 cm−1 with wavelength of 540 nm in the visible region was predicted, reflectivity of 0.52, refractive index of 4.3 and extinction coefficient of 4.7 shows the optical potential of the compound when compared to other chalcogenide and halide perovskites. Hence, an attractive non-toxic, stable, and cost-effective material for photovoltaic application.

Tunable band gap energy of single-walled zigzag ZnO nanotubes as a potential application in photodetection

ZnO nanotubes play a substantial role in various optoelectronic applications such as light-emitting diodes, solar cells and photodetectors. In this study, the structural, electronic, and optical effects of (n,0) single-walled ZnO nanotubes with different radius are discussed. An ab-initio approach of density functional theory with the generalized gradient approximation has been done by Quantum ESPRESSO software on nanotubes with n = 3 to 6. All simulated ZnO nanotubes illustrate semiconducting behavior, which due to the quantum confinement effect, the band gap value decreases by the increase in diameter. Moreover, optical characteristics including dielectric function ε(ω), refractive index n(ω), optical absorption coefficient α(ω), conductivity σ(ω), energy loss spectrum L(ω) and reflectivity R(ω) have been analyzed and compared. The predicted optical features show that the mentioned nanotubes transmit light in perpendicular polarization better than parallel one and present superior reflect characters. Additionally, ZnO NTs act as a good absorbent in the visible wavelength which they can absorb various colors of the visible spectrum or even UV emission by altering the number of n. This ability turns ZnO NTs into remarkable photodetectors. Furthermore, according to optical characteristics like energy loss spectrum and dielectric function, it is obvious that results are approximately similar for different nanotubes and despite the miner red-shift of the position of the main peak, their appearance is close to each other. Therefore, ZnO NTs can be utilized in various applications such as optical filters, polarizers, and UV shields.

Graphitic carbon nitride nanosheet as an excellent compound for the adsorption of calcium and magnesium ions: theoretical and experimental studies

In this work, the removal of calcium (Ca2+) and magnesium (Mg2+) ions were studied using graphitic carbon nitride (g-C3N4) nanosheet as an adsorbent from aqueous solutions. In experimental studies, the effects of various adsorption parameters were investigated by batch method culture including pH, initial Ca2+ and Mg2+ concentrations, temperature, time, and adsorbent mass. The best results were obtained at pH=8.50, 0.05 g of g-C3N4, 90 min, 10 ppm of ion concentration, 23.80 mg g-1 of maximum adsorption capacity for Ca2+, and pH=9, 0.05 g of g-C3N4, 60 min, 15 ppm of ion concentration, 40.00 mg g-1 maximum adsorption capacity for Mg2+ ion. The adsorption of calcium and magnesium ions obeyed the Langmuir model on adsorbent. In theoretical study, g-C3N4 nanosheet as an interesting material was studied by first-principle calculation using the Quantum Espresso package. The Ca2+ and Mg2+ ions were located at different positions on g-C3N4 nanosheet to obtain the stable configuration. The Eads, HOMO, LUMO, Eg, band structure, DOS and PDOS plots were investigated at stable configuration of g-C3N4 nanosheet. The adsorption energy (Eads) was calculated -15.55 and -26.24 eV for Ca2+ and Mg2+ ions, respectively. Further, the results indicated that Mg2+can be located at the center of the porous g-C3N4 nanosheet, which the adsorption of Mg2+ on surface of g-C3N4 nanosheet was stronger than that of Ca2+ ion. Theoretical and experimental data confirmed each other’s findings. The adsorption of Ca2+ and Mg2+ ions was shown to be simple, high-yield, eco-friendly, and economical performance from aqueous solutions using g-C3N4 nanosheet

Study of the solar perovskite CsMBr3 (M=Pb or Ge) photovoltaic materials: Band-gap engineering

In this paper, we study the organometal lead halides (OLH) based perovskite solar cells (PSC). In fact, we investigate and discuss the electronic properties of the novel solar perovskites CsMBr3 (M = Pb or Ge) materials, using the DFT method combined with the Quantum Espresso package. Moreover, the effect of the lattice parameter and the number of layers on the band gap value of the solar perovskites photovoltaic CsMBr3 (M = Pb or Ge) have been improved. Indeed, we inspect the structural properties of the studied materials and found that the optimized lattice parameter is equal to 6.0 Å for the solar perovskite material CsPbBr3. While, for the solar material CsGeBr3, the optimized lattice parameter value is 5.7 Å. In addition, it is found that the band gap value increases for increasing the lattice parameter values for the two materials. On the other hand, when increasing the number of layers of the solar perovskites CsMBr3 (M = Pb or Ge), the total energy decreases. Furthermore, the band gap crosses through a maximum before decreasing more and more for sufficiently large number of layers. • The Solar Perovskites CsMBr3 (M = Pb or Ge) have been studied. • The DFT method has been applied. • The Band gap energies have been investigated. • The Layer numbers effects have been outlined.

Investigation of pressure dependence of mechanical properties of SbSI compound in paraelectric phase by Ab Initio method

The structural parameters as atomic positions, lattice constants, volume and density were determined using the Quantum Espresso software by geometric optimization at ambient pressure and under hydro static pressure. Using optimized values, elastic constants were calculated. The pressure dependence of elastic modulus (bulk, Young and shear modulus, Poisson ratio), anisotropy, compressibility and Debye temperatures were investigated using the calculated elastic constants. Mechanical stability and ductility/brittleness of the material were evaluated. It was seen that the results obtained were compatible with the existing experimental and theoretical data.

Prediction of half-metallicity and spin-gapless semiconducting behavior in the new series of FeCr-based quaternary Heusler alloys: An Ab initio study

This paper presents a detailed investigation of FeCr-based quaternary Heusler alloys. By using ultrasoft pseudopotential, electronic and magnetic properties of the compounds are studied within the framework of Density Functional Theory (DFT) by using the Quantum Espresso package. The thermodynamic, mechanical, and dynamical stability of the compounds is established through the comprehensive study of different mechanical parameters and phonon dispersion curves. The meticulous study of elastic parameters such as bulk, Young’s, shear moduli, etc. is done to understand different mechanical properties. The FeCr-based compounds containing also Yttrium are studied to redress the contradictory electronic and magnetic properties observed in the literature. The interesting properties like half-metallicity and spin-gapless semiconducting (SGS) behavior are realized in the compounds under study.

Study of Electronic and Magnetic Properties of Single Layered Graphene with Vacancy and (-OH) Adsorption by Density Functional Theory Calculation

Graphene is one of the most popular two-dimensional materials. However, a zero bandgap character of graphene restricts some nanoelectronics uses. Thus a defect or functional group is generally introduced to create magnetism in graphene Here, we study electronic and magnetic properties of single-layered graphene having a vacancy and hydroxide (-OH) adsorption. The calculation is performed by employing the spin-polarized density functional theory (DFT) method using the Quantum Espresso package. Modeled systems used in the calculation are the 4x4x1 graphene supercell (G), single vacancy graphene (SVG), and SVG with OH adsorption (G-OH). The band gaps calculated from SVG obtained 1.2 eV (spin-up) and 0.7 eV (spin-down), and G-OH obtained 0.8 eV (spin-up) and 1.2 eV (spin-down) after optimized structure. Moreover, the magnetic moment is estimated to be 0.69 μ B per cell and 1.00 μ B per cell for SVG and G-OH, respectively. The result shows that the defect influences electronic and magnetic properties on graphene. The results of this analysis can be used for future research of graphene applications.

Structural, electronic and magnetic properties of S sites vacancy defects graphene/MoS2 van der Waals heterostructures: First-principles study

In this work, we investigated the geometrical structures, electronic and magnetic properties of S sites vacancy defects in heterostructure graphene/molybdenum disulphide ((HS)G/MoS[Formula: see text] material by performing first-principles calculations based on spin polarized Density Functional Theory (DFT) method within van der Waals (vdW) corrections (DFT-D2) approach. All the structures are optimized and relaxed by BFGS method using computational tool Quantum ESPRESSO (QE) package. We found that both (HS)G/MoS2 and S sites vacancy defects in (HS)G/MoS2 (D1S–(HS)G/MoS2, U1S–(HS)G/MoS2, 2S–(HS)G/MoS2 and 3S–(HS)G/MoS[Formula: see text] are stable materials, and atoms in defects structures are more compact than in pristine (HS)G/MoS2 structure. From band structure calculations, we found that (HS)G/MoS2, (D1S–(HS)G/MoS2, U1S–(HS)G/MoS2, 2S–(HS)G/MoS2 and 3S–(HS)G/MoS[Formula: see text] materials have [Formula: see text]-type Schottky contact. The Dirac cone is formed in conduction band of the materials mentioned above. The barrier height of Dirac cones from Fermi energy level of (HS)G/MoS2, (D1S–(HS)G/MoS2, U1S–(HS)G/MoS2, 2S–(HS)G/MoS2 and 3S–(HS)G/MoS[Formula: see text] materials have values 0.56[Formula: see text]eV, 0.62[Formula: see text]eV, 0.62[Formula: see text]eV, 0.64[Formula: see text]eV and 0.65[Formula: see text]eV, respectively, which means they have metallic properties. To study the magnetic properties of materials, we have carried out DoS and PDoS calculations. We found that (HS)G/MoS2, D1S–(HS)G/MoS2 and U1S–(HS)G/MoS2 materials have non-magnetic properties, and 2S–(HS)G/MoS2 and 3S–(HS)G/MoS2 materials have magnetic properties. Therefore, the non-magnetic (HS)G/MoS2 changes to magnetic 2S–(HS)G/MoS2 and 3S–(HS)G/MoS2 materials due to 2S and 3S atoms vacancy defects, respectively, in (HS)G/MoS2 material. Magnetic moment obtained in 2S–(HS)G/MoS2 and 3S–(HS)G/MoS2 materials due to the unequal distribution of up and down spin states of electrons in 2s and 2p orbitals of C atoms; 4p, 4d and 5s orbitals of Mo atoms; and 3s and 3p orbitals of S atoms in structures. Magnetic moment of 2S–(HS)G/MoS2 and 3S–(HS)G/MoS2 materials is −0.11[Formula: see text][Formula: see text]/cell and [Formula: see text]/cell, respectively, and spins of 2p orbital of C atoms, 3p orbital of S atoms and 4d orbital of Mo atoms have dominant role to create magnetism in 2S–(HS)G/MoS2 and 3S–(HS)G/MoS2 materials.

Sulfur doping effect on the electronic properties of zirconium dioxide ZrO2

In this paper, we use density functional theory (DFT) calculations under Quantum Espresso package to characterize the doping effect of sulfur substitution on Zirconium dioxide ZrO2. Through the density of states (DOS) and the band structure (BS) calculations, a direct band gap is found for the pure and doped studied ZrO2 system. The optoelectronic properties analysis shows that the doping with sulfur could considerably decrease the band gap of doped ZrO2 by the presence of an impurity state of sulfur 3p on the up spin of the valence band. The results of the ab-initio density functional theory investigations show that the substitution by sulfur dopants incorporated into the Zirconium dioxide ZrO2 drastically and affect the electronic structure of the studied material. Thus, the doped ZrO2 with sulfur impurities can improve interesting properties in photovoltaic applications. In fact, the doping of Zirconium dioxide ZrO2 with appropriate concentration values of sulfur leads to band gap values in the interval (1–2) eV.

Halogens Substitution Effects on Electronic and Spectral Properties of Carbon Nanotube Molecules studying with the DFT method

The carbon nanotubes (CNTs) in a zigzag (4, 0) shape before and after substituted with F, Cl, and Br atoms were used as a basic computer model depending on the Quantum Espresso package DFT process (in the present work. This method demonstrated that the electronic structure, bandgap, total energy, FTIR spectrum, Raman spectrum, and depolarization spectrum can all being calculated. The simulated results are discovered that the increase in impurity atom size from F to Br as donor groups on nanotubes reduce the energy gaps from 0.959 eV to 0.674 eV, the ionization potentials from 6.088 eV to 5.729 eV, the electron affinities from 5.129 eV to 5.054 eV, and the firm energies from 5.609 eV to 5.392 eV. As a result, these substituted compounds have a high activity to act as a catalyst with broad absorption bands of the solar spectrum in the following order: Br+CNTs > Cl+CNTs > F+CNTs > CNT. This behavior will provide a better output for the solar cells and photovoltaic devices. The increment in HOMO, LUMO, and total energy magnitudes with increasing the impurity atom size from F to Br is given maximum changes, decreases band gaps, and elevated entropy values because of elevating in random.

A DFT Investigation on Structural and Electronic Properties of Pure and Sr-Doped Wurtzite ZnO

The aim of this study was to investigate structural and electronic properties of pure and Strontium-doped wurtzite ZnO using first principles density functional calculations (DFT). The first principle calculation is a computational method to study the electronic structure of materials. The self-consistent calculation was done using Generalized Gradient Approximation (GGA) with BLYP functional implemented on Quantum ESPRESSO package to generate the band structure and density of states of the materials taken under consideration. The Strontium doping caused the increase in lattice volume and slight distortions at the unit cell parameters in a wurtzite structure. This doping process increased the band-gap energy (E g ) at low percentage 25% (E g = 1.55eV) and 50% (E g = 2.33eV) with indirect band-gap and direct band gap at high percentages 75% (E g = 2.38eV) and 100% (E g = 3.368eV), which we call it wide direct band gap. The lattice parameters obtained at the level of GGA–BLYP approach was found to be (a = b = 3.412A o , and c = 5.205A o ) in good agreement with either previously reported theoretical or experimental work. The calculated band-gap of the pure wurtzite ZnO is found to be 0.935eV. This is a new result because in our knowledge nobody has been work in wurtzite ZnO used the exchange correlation BLYP functional based on DFT. Compared with experimental value (3.37eV), the calculated band-gap was much smaller because of the well-known conduction band, but the result did not affect the accuracy of the comparison of the related properties of the crystals. The results obtained can be used as a basis for more in depth calculations, which may include calculating the optical properties with additional dopant that can be used on optical and photo-catalytic applications.

High-Performance Ru 2 P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

High-Performance Ru ₂ P Anodic Catalyst for Alkaline Polymer Electrolyte Fuel Cells

Theoretical study of ThO2 by first principles calculations

In this paper, the thermodynamic, structural properties and vibrational spectrum of thorium dioxide have been studied using the Density Functional Perturbation Theory (DFPT) and Density Functional Theory (DFT) in the framework of first principles calculations. Quantum espresso software, which is an open source computing code, has been used in order to compute the kohn-Sham equations to obtain the minimum total energy of crystal. The vibrational spectrum of the thorium dioxide was examined along various symmetrical directions, and the results showed the dynamical stability of the crystal system. The quasi-harmonic Debye-Einstein model as implemented in GIBBS2 Code was used to calculate the thermodynamic properties of thorium dioxide at high temperatures and pressures. The simulation results showed that the Debye temperature of thorium dioxide decreased with increasing temperature at a constant pressure and increased with increasing pressure at a constant temperature. Increasing the Debye temperature indicated an increase in the crystal stiffness and the average sound velocity. It was observed that the volumetric thermal expansion coefficient and gruneisen parameter decreased exponentially with increasing pressure at a constant temperature, while increased with increasing temperature at a constant pressure, indicating an increase in heat transfer in the crystal lattice

Transport Properties of CoSi and Solid Solutions of Co1 – xMxSi (M = Fe, Ni)

We study the thermoelectric and galvanomagnetic properties of cobalt monosilicide (CoSi) and its solid solutions with FeSi and NiSi. Recent CoSi band structure calculations, confirmed by ARPES measurements, revealed several differences of the electronic structure from the previous standard two-band model for semi-metallic compounds. The discovered features of the CoSi band structure require modifications of previously used models for description of material transport properties. We investigate the temperature dependences of the Seebeck coefficient, electrical resistivity, and Hall coefficient in the temperature range from 100 to 800 K for CoSi and for its solid solutions with FeSi and NiSi. The ab initio calculation of the band structure and transport coefficient were carried out using the Quantum Espresso software package. The results of the study showed that the main features of the thermoelectric and galvanomagnetic properties of CoSi and its solid solutions with FeSi and NiSi at high temperatures can be adequately described using the ab initio calculated band structure, taking into account the energy dependence of the relaxation time.

Band gap energy calculation of theaflavin and Cyanidin-3-Glucoside molecules as active material in Dye Sensitized Solar Cells using Density Functional Theory (DFT)

Dye-Sensitized Solar Cell (DSSC) is one of photovoltaic (PV) cell which converts solar energy into electrical energy, by using dye as its active material. In this study, total energy and bandgap energy of natural dyes such as theaflavin and cyanidin-3-glucoside (C3G) molecules were calculated using density functional theory (DFT) method via quantum espresso software. Optimization of some calculation parameters such as cutoff energy, pseudopotential and k-point have been done to ensure minimum total energy of dyes molecule. Based on the result, the total and bandgap energy of theaflavin is 10172.80 eV and 1.96 eV, while the total and bandgap energy of the C3G molecule is 8442.26 eV and 1.73 eV. From these results, further investigation is necessary to the opportunities of the two dyes as DSSC sensitizers.

Application of zinc oxide nanosheet in various anticancer drugs delivery: Quantum chemical study

Zinc oxide nanosheet (ZnONS) is a promising road to deliver numerous anticancer drugs (5-FU, 6-MP, GB, and CP) in the human body. The electronic properties of the anticancer drugs/ZnONS studied by using DFT method, which implemented in the quantum espresso package. Our finding shown that ZnONS has a semiconductor behavior. Interestingly, the electronic band gap of the 5-FU/ZnONS and GB/ZnONS is decreased, but they still have semiconductor behaviors. For 6-MP/ZnONS, it is increased and converted to n-type semiconductor for CP/ZnONS structure. According to acquired findings, the complex structures became more stable and lower reactive due to the total energy of these complex structures is increased compared to pristine ZnONS. All complex structures are required higher excitation energy to transfer an electron due to the chemical hardness of all complex structures is decreased, but the 6-MP/ZnONS structure has the opposite behavior. There is a weak interaction between ZnONS and (5-FU, 6-MP, and GB) and good interaction between the ZnONS and CP due to the electrophilic of these structures has lower and higher values, respectively. Concisely, ZnONS considered the greatest substrate to carry all these anticancer drugs.

Estimation of the workload of a hybrid computing cluster when performing modeling tasks in materials science

The article is devoted to methods of calculation and evaluation of the efficiency of functioning of hybrid computing systems. Material science software systems demonstrate maximum efficiency when operating on hybrid computing systems when using graphics accelerators for calculations. Examples include the VASP (The Vienna Ab initio Simulation Package) and Quantum ESPRESSO software systems. These software systems are most efficient when using monopolistic computing resources: RAM, CPU, GPU.When operating a hybrid high-performance cluster, the problem arises of resource management and their division between a group of users. Technologies need to be developed that ensure the allocation of resources to materials science applications for different users and research teams. The modern approach to organizing the computing process is the use of virtualization and cloud technologies. Cloud technologies enable the provision of SaaS and PaaS services to users. It is advisable to provide scientific teams with applied materials science systems as cloud services.Such diverse approaches, when applied in a single computer complex, require the development of methods for optimizing the load on the resources of a high-performance complex, assessing the efficiency of using its computational capabilities, and developing methods for improving user programs.Determining the quality of the complex loading is an important task when providing high-performance computing services to research teams performing interdisciplinary research in various fields of science and technology. The article proposes a method for calculating the value of the load value using the peak performance values of the complex. The results and performance quality of high performance computing cloud scientific services are analyzed using a Roofline model.

Calculation of the band structure and density of localized states of materials of the quasi-binary system Zn3As2–Mn3As2

Investigations of materials of the quasi-binary system Zn3As2–Mn3As2 have been performed. We present band structure calculations of crystal structures of Zn3As2, Mn3As2 and ZnMn2As2 within the framework of the density functional theory (DFT) and DFT + U method. The calculations based on first-principles were made using plane waves normalized on pseudopotential with the Quantum Espresso software package. Was obtained, that fundamental gap for Mn3As2 and Zn3As2 is equal to the optical band gap, while the band gaps for ZnMn2As2 was closer. The calculation for Mn3As2 and ZnMn2As2 by method DFT + U were performed; in these cases, the fundamental band gaps are closer to the optical band gaps, respectively. Considering the series Zn3As2 → ZnMn2As2 → Mn3As2, an increase in the Fermi energy was observed: Ef = 7.5 → 8.98 → 12.04 eV. It was established that the band gap of ZnMn2As2 (Eg = 0.6 eV) is a direct band gap corresponding to the transition between points Γ→Γ of the Brillouin zone. The Eg value obtained by us is closely known from experiments on optical absorption and the study of the temperature dependence of resistivity with Eg values equal to 0.8 eV and 0.76 eV, respectively. For Mn3As2 and ZnMn2As2, splitting is observed in density of states (DOS) between spin up and spin down electrons.

First-principles study of structure, electronic, and magnetic properties of C sites vacancy defects in water adsorbed graphene/MoS2 van der Waals heterostructures.

We have studied structure, electronic, and magnetic properties of water adsorbed vdW heterostructure graphene/MoS2 (w-(HS)G/MoS2) and its C sites vacancy defects materials (w-Catoms-vacancy-(HS)G/MoS2) by using a spin polarized density functional theory (DFT) method of calculations within DFT-D2 approach to take in to account of vdW interactions. All the structures are optimized and relaxed by BFGS method using computational tool Quantum ESPRESSO package. By structural analysis, we found that both w-(HS)G/MoS2 and w-Catoms-vacancy-(HS)G/MoS2 are stable materials. The stability and compactness of these materials decrease with an increase in their defects concentrations. From band structure calculations, our findings show that w-(HS)G/MoS2 has a metallic nature, and there is formation of n-type Schottky contact of barrier height 0.42eV. Also, the left 1C atom vacancy defects in w-(HS)G/MoS2 (L1C-w-(HS)G/MoS2) and center 1C atom vacancy defects in w-(HS)G/MoS2 (C1C-w-(HS)G/MoS2) materials have no band gap for up and down spin electronic states, indicating that they have also a metallic nature. On the other hand, 2C atom vacancy defects in w-(HS)G/MoS2 (2C-w-(HS)G/MoS2) has a small band gap for up spins states and no band gap for down spin electronic states which means that the band structure resembles with half metallic nature. Thus, the endowment of metallic nature decreased with increase in the concentrations of defects in structures. To study the magnetic properties in materials, DOS and PDOS calculations are used, and we found that non-magnetic w-(HS)G/MoS2 material changes to magnetic in all the three different L1C-w-(HS)G/MoS2, C1C-w-(HS)G/MoS2, and 2C-w-(HS)G/MoS2 materials with vacancy. L1C-w-(HS)G/MoS2, C1C-w-(HS)G/MoS2, and 2C-w-(HS)G/MoS2 have magnetic moments of + 0.21μB/cell, + 0.26μB/cell, and - 2.00μB/cell, respectively. The spins of electrons in 2s and 2p orbitals of C atoms give a principal effect of magnetism in w-Catoms-vacancy-(HS)G/MoS2 materials.