Ultrasoft Pseudopotentials Research Articles

Correlated Electronic and Opto-magnetic Properties of Cobalt Doped GaN

The effect of cobalt doping on the electronic, magnetic and optical properties of GaN has been investigated using density functional theory (DFT) first-principles calculations within the framework of generalized gradient approximation suggested by Perdew-Burke Ernzerhof and ultrasoft pseudopotential. The electronic band structure of cobalt (Co) doped GaN turns into half metallic rather than semiconducting in its pure form and reduces significantly too. The values of magnetic moment at Co and nitrogen (N) sites are 0.8 μB and 0.12 μB, respectively. The effect of the increase in Co concentration results in reduced spin-polarization and the Co magnetic moment itself. According to phenomenological band structure model, the p-d repulsion increases with increasing Co concentration, which subsequently lowers the spin-polarization and hence the d-d coupling increases due to possible charge transfer between Co t2d and ed states. The Co d-Dos diagram for various doping concentrations exhibits more broadened t2d levels, thus predicting the increase in stability with increase in dopant concentration. The coupling between Co atoms is ferromagnetic, mediated through neighboring Ga and N atoms. The absorption edge of Co-doped GaN manifests a red shift with the increase in doping concentration. These findings are in good agreement with the experimental results. We predict that a lower concentration of cobalt-doped GaN is appropriate for spintronic applications.

Structural, Electronic, and Optical Properties of Ga-Based Lead-Free Mixed-Halide Perovskites Cs3GaI6-xBrx (0 ≤ x ≤ 6) for Solar Cell Applications: A DFT Study

Lead-free perovskite solar cells (PSCs), such as the mixed-halide perovskites (MHPs) ones, are promising devices in order to overcome the inherent problems of instability and toxicity of the lead-based PSCs. This is the first study that reports on Ga-based lead-free mixed halide perovskites with a general formula of Cs3GaI6-xBrx for 0 ≤ x ≤ 6, investigated by CASTEP with norm-conserving and Vanderbilt ultrasoft pseudopotentials along the projector augmented wave (PAW) method (for core-level properties) in the framework of density functional theory (DFT). The role of Ga at the B position of the perovskite structure ABX3 was investigated. The effect of increasing of I concentration was thoroughly determined. The investigated compounds manifest good structural stability and have energy bandgaps close to the Shockley-Queisser limit of 1.34 eV. The bandgaps of Cs3GaI2Br4, Cs3GaI3Br3, Cs3GaI4Br2, and Cs3GaI5Br were calculated as 1.779, 1.615, 1.354, and 1.319 eV, respectively. The optical absorption coefficients of the investigated MHPs lie in the range of 104 per cm. Among the investigated materials, Cs3GaI4Br2 and Cs3GaI5Br are recommended for solar cells and other photovoltaic applications.

Taming the optical response via (Ca:Zr) co-doped impurity in c-BaTiO3: A comprehensive computational insight

The lead-free Ca and Zr doped BaTiO3 is the focus of different research groups owing to its greater piezoelectricity and superior dielectric properties. To dig out the reason of these superior features at atomic scale, the density functional theory (DFT) based first principles calculations are implemented to study Ca:Zr doped barium titanate (BTO), by using Ultrasoft Pseudopotential (USP) as incorporated in CASTEP. The BTO has been doped with calcium (Ca) and zirconium (Zr) at barium and titanium sites respectively, individually and in co-doped form, to tailor the electronic bandgap. The band structure, density of states (DOS) and optical properties of both the singly doped as well as co-doped BTO structures are presented. A transition of indirect bandgap to the direct one is evident in all cases due to the Brillouin zone folding. In case of Ca-doping (BCTO), the shifting of Fermi level towards the valence band is inferred as converting BTO to a p-type material to some extent, with bandgap decreasing from 1.726eV to 1.714eV. Whereas, considering the case of Zr-doping (BZTO) and Ca:Zr doping (BCZTO), the Fermi level was found to be shifted towards the conduction band making the material an n-type and bandgap increased to the values of 1.776 eV and 2.654 eV respectively. The change in structural properties is observed to affect the optical properties of the material upon doping. The comparative analysis of absorption, refractive index, reflectivity, dielectric constant, and extinction coefficient and energy loss function for pure and doped systems have been presented. The doping changed optical behavior of barium titanate making the material more useful for optoelectronic applications.

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.

Study on quaternary diamond-like Li2CaGeO4 properties for optoelectronic applications

The materials properties of quaternary diamond-like Li2CaGeO4 have been studied. The computations are used through the full-potential linearized augmented plane wave method within the local orbitals and ultra-soft pseudo-potentials. Calculated structural parameters are found to be accordant with those of experiment. The elastic anisotropy of the crystal under focus is visualized and discussed. The calculated elastic constants Cij can permit the determination of the macroscopic mechanical parameters of the material under focus. The low-values of bulk modulus and shear modulus indicate that the material under focus should be a soft material. The higher is the value of the Young's modulus, the stiffer is the material of interest. The material under study is found to be an H→Г indirect band gap semiconductor. The main contributions are due to the Li-p and Li-s orbitals. By increasing the temperature results in a slight decrease of the dielectric constant. The authors findings regarding the electronic and optical spectra reveal that the candidates of interest can be a promising materials in optoelectronic devices for visible and ultraviolet domains.

First-principles calculation of the electronic structure, elastic and optical properties of LiSn2N3 nitrogen base stable perovskite semiconductor material

SemiconductingII-IV-N2 ternaries (for example, Zn2+ and Ge4+ instead of Ga3+) are becoming more common. These heterovalent wurtzite-derived compounds may change metal composition and cation disorder to alter electrical characteristics. this method works with transition metal nitrides formations. One reason group IV transition metals are metallic is because they are often found in nitrides (e.g. TiN). The addition of electropositive low-valence alkaline earth (AE) cations, such as Mg2+, closes the d-shell and promotes semiconductivity. A few metal base derivatives (e.g., SrZrN2, SrHfN2[14]) have been synthesized, however, there is a dearth of data on crystal structure and their functional characteristics. DFT is used in all computations, as executed in the QUANTUM ESPRESSO suite. The gradient corrected Perdew–Burke–Ernzerhof (PBE) functional was used to determine the exchange and correlation energies. Vanderbilt ultrasoft pseudopotentials. are used for the Sn (3d5, 4s2) and N valence electrons (2s2, 2p3). Brillouin zones required 0.01 Ry Methfessel Paxton smearing and a k-point grid of 8 × 8 × 8. This is because the Khon-Sham states are extended in-plane waves with minimized kinetic energy, cutoffs of 500 eV, and 10 times the charge density. The electronic band structure and projection total density of states of a stable perovskite semiconducting material, LiSn2N3, have been estimated (TDOS). The electron band channel (red line) of LiSn2N3 exhibits a direct bandgap of 0.78 eV between the Brillouin zone's G–Z high symmetry sites. These results support the idea that LiSn2N3 might be utilized to create customizable high stability solar cells findings.

Vacancy Induced Magnetism and Spin Filtering in 2D GaN Monolayer

Exotic properties functionalized by Ga or N atom vacancies in two-dimensional GaN monolayer have been predicted for the first time. A detailed ab-initio study of the structural, electronic, magnetic and optical properties of a 2D–GaN monolayer containing Ga or N atom vacancies has been performed. In the present study, we make two refinements in the density functional theory. At first, long range dispersion interactions not discussed so far have been accounted for. Further, norm-conserving pseudopotentials and plane waves are employed in generalized gradient approximation in contrast to earlier workers who have used soft or ultra-soft pseudopotentials. One observes that the strength of induced magnetism depends not on the separation of Ga-vacancies but on the number of Ga atom vacancies. The magnetism induced by N-atom vacancies is either zero or quite small. Spin filtering has been observed in many configurations. A strong continuous absorption from the far infrared region to the deep visible region is seen in some systems. It may be useful for development of photo-emitting devices which will emit in various regions of energy spectrum including visible emission. The emission of 2D-GaN monolayer lying in deep ultraviolet region may be used for sterilization, water purification etc.

Calculating dynamical mean-field theory forces in ab initio ultrasoft pseudopotential formalism

In this paper, we show how to calculate analytical atomic forces within self-consistent density functional theory + dynamical mean-field theory (DFT+DMFT) approach in the case when ultra-soft or norm-conserving pseudopotentials are used. We show how to treat the non-local projection terms arising within the pseudopotential formalism and circumvent the problem of non-orthogonality of the Kohn-Sham eigenvectors. Our approach is, in principle, independent of the DMFT solver employed, and here was tested with the Hubbard I solver. We benchmark our formalism by comparing against the forces calculated in Ce$_{2}$O$_{3}$ and PrO$_2$ by numerical differentiation of the total free energy, as well as by comparing the energy profiles against the numerically integrated analytical forces.

Carbon doping effect on the optoelectronic properties of the KNO3 material

In this work, we present studies based on the two methods density functional theory (DFT) and time-dependent density functional theory (TDDFT) to illustrate the optoelectronic properties of the pure and doped KNO3. In fact, the used DFT method is carried out under the Quantum Espresso package. Moreover, our investigations are performed on the basis of the generalized-gradient approximation of Perdew–Burke–Eruzerhof without and with the spin orbit coupling (SOC) correction. The ab-initio calculations of the studied compound have been performed while relying to the DFT, using the Quantum Espresso code. The obtained results and calculations are simulated under norm-conserving pseudo-potentials for calculations without SOC calculations and fully-relativistic ultra-soft pseudo-potentials for SOC calculations. The width of the Gaussian smearing was set to 0.1 eV. It has been found that the main result of the doping effect is to decrease the energy band gap of the KNO3. While, the gap nature is still direct in the Γ point in both pure and doped cases.

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.

Density Functional Theory‐Based Prediction of the Pressure‐Dependent Magnetic Properties of CaRuO3

Using the density functional theory with the plane‐wave ultrasoft pseudopotentials method within the local density approximation (LDA), the magnetic structure of CaRuO3 (hereafter referred to as CRO) is studied as a function of hydrostatic pressure. The calculated results show that: 1) the compressive stress does not cause the disappearance of the ferromagnetic (FM) ground state of cubic CRO but only reduces the magnetic ordering energy and magnetic moment per formula unit, and that 2) the orthorhombic CRO with the Pbnm structure is just in the critical region of the FM, antiferromagnetic (AF), and paramagnetic ground states. Although there is no evidence of an AF phase of CRO at low temperature, the calculated results show that an AF interaction does exist between the Ru atoms of CRO. This can explain the negative Weiss temperature of CRO and the abnormal behavior of the magnetic susceptibility of CRO at low temperature. The AF interaction and the sensitivity to the crystal structure may be the reasons for the various properties of CRO.

Diradicals or Zwitterions: The Chemical States of m -Benzoquinone and Structural Variation after Storage of Li Ions

Diradicals or Zwitterions: The Chemical States of <i>m</i> -Benzoquinone and Structural Variation after Storage of Li Ions

Study of structural and electronic properties of intercalated CrTiS2 compound by density functional theory

In the present paper, we report the structural optimization of intercalated CrTiS2 compound by using Density Functional Theory (DFT) with Generalized Gradient Approximation (GGA) through Quantum ESPRESSO code. All the computations are carried out by using an ultra-soft pseudopotential. The effect of charge transfer from guest 3d transition metal Cr-atom to self-intercalated compound TiS2 has been studied. In electronic properties, the energy band structure, total density of states (TDOS), partial density of states (PDOS) and Fermi surface have carried out. From the energy band structure, we conclude that the TiS2 -intercalated compound has a small bandgap while the doped compound with guest Cr-atom has metallic behavior as shown form its overlapped band structure.

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.

Influence of (Li/Na/K) doping and point defect (VAl, Hi) on the magnetic and photocatalytic performance of AlN: A first-principles study

Although extensive reports on the influence of Li/Na/K doping on the physical properties of AlN systems exist, the effects of Li/Na/K doping and point defects (VAl, Hi) coexisting in AlN systems on magneto-optical properties are often neglected. Experimentally, Li/Na/K doping and point defects (VAl, Hi) cannot be precisely controlled. In this study, the generalized gradient approximation (GGA) plane wave ultrasoft pseudopotential + U method based on spin density functional theory is adopted to solve the abovementioned problem. The first-principles method is utilized to study the effects of point defects (VAl, Hi) and Li/Na/K doping on the photocatalytic performance of AlN systems. Compared with the Al34MN36 (M = Li/Na/K) system, the Al34MHiN36 (M = Li/Na/K) system presents reduced formation energy and improved stability. The Al34NaHiN36 system has the smallest formation energy and the highest stability. In particular, compared with all doped systems, the Al34NaHiN36 system has the best absorption spectrum redshift, the best carrier activity, the longest carrier lifetime, and the strongest oxidation capacity, that is, the best photocatalytic performance. The first-principles study indicates that N atoms in all Al34MN36 (M = Li/Na/K) and Al34MHiN36 (M = Li/Na/K) systems have acceptor and donor characteristics. The magnetic source of all doped systems is related to the double exchange of carriers as mediators, the itinerant electron polarization of unpaired N2− atoms and electric polarization. This study has certain theoretical guidance for the experimental design and preparation of new AlN magneto-optical functional materials.

Vacancies effect on structural, electronic and mechanical properties of delafossite CuAlO2

Delafossite-structured CuAlO2 materials with and without vacancy defects were investigated comparatively using the first principle calculation method. The method based on the density functional theory, has been carried out to search the systems’ ground states and supplies the corresponding electronic properties. In the process of calculations, ultrasoft pseudo-potentials and PBE-GGA functionals are chosen for the atoms and exchange-correlation interactons between electrons, respectively. The geometry optimization shows the Al vacancy causes a larger lattice deformation than the vacancies of Cu and O atoms. The results of Mulliken charge also verify this conclusion. The calculations of vacancy formation energy and elastic constants indicate the Cu vacancy has the lowest formation energy, the highest Pugh ratio and the smallest Zener anisotropy factor, which means the introduction of Cu vacancy can improve the functional applications of Cu-based delafossites, e.g. p-type conductivity, ductility, etc.

Effect of different Mn doping and point vacancy ratios on the magnetic properties of ZnO

The magnetic source of Mn doping and Zn vacancy coexisting in ZnO is controversial. To solve this problem, this work used the generalized gradient approximation first-principles plane-wave ultrasoft pseudo potential + U method based on density functional theory to calculate the effect of different Mn doping to point vacancy ratios on the magnetic properties of ZnO. The formation energy of ZnO with different Mn-substituted Zn (MnZn) to oxygen/zinc vacancy (VO/VZn) ratios can be smaller and more stable in zinc (Zn)-rich conditions than in oxygen (O)-rich conditions. The ZnO system exhibits p-type half-metallic ferromagnetism when the MnZn to VZn ratio is 2:1 or 2:2. When the Mn doping amount is constant, the Zn vacancies increase and the total magnetic moment of the doped system decreases. For the ZnO system in which Mn doping and oxygen vacancies coexist, when the amount of oxygen vacancies is constant, with Mn doping increase, the magnetic moment becomes larger. Both Zn22Mn2O22 and Zn20Mn2O24 can achieve ferromagnetic characteristics above room temperature.

Theoretical Study of Transition Metal Dichalcogenides Compound TiS2 and Their Intercalated Compound CrTiS2 Using Density Functional Theory

The Density Functional Theory (DFT) based computational study is carried out for the transition metal dichalcogenides (TMDCs) compound TiS2 and their intercalated 3d transition metal compound CrTiS2. It is carried through Generalized Gradient Approximation (GGA) through Quantum ESPRESSO environment employing Perdew-Burke-Ernzerhof (PBE) exchange and correlation effect with an ultra-soft pseudopotential. In the present work, the structural optimization and electronic properties like energy band structure, density of states (DOS), partial or projected density of states (PDOS), total density of states (TDOS), Fermi surfaces and charge density are reported. The effect of charge transfer from guest 3d transition metal Cr-atom to self-intercalated compound TiS2 has been observed. While, the energy band structure of CrTiS2 compound is computed in the non-magnetic state. From the energy band structure of said materials, we conclude that the TiS2 compound has an indirect narrow band gap though the CrTiS2 compound has an overlapped band structure. The TiS2 shows a semiconductor or semi-metallic nature while doped compound with guest Cr-atom has a metallic material..

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....

Perturbo: A software package for ab initio electron–phonon interactions, charge transport and ultrafast dynamics

Perturbo is a software package for first-principles calculations of charge transport and ultrafast carrier dynamics in materials. The current version focuses on electron–phonon interactions and can compute phonon-limited transport properties such as the conductivity, carrier mobility and Seebeck coefficient. It can also simulate the ultrafast nonequilibrium electron dynamics in the presence of electron–phonon scattering. Perturbo uses results from density functional theory and density functional perturbation theory calculations as input, and employs Wannier interpolation to reduce the computational cost. It supports norm-conserving and ultrasoft pseudopotentials, spin–orbit coupling, and polar electron–phonon interactions for bulk and 2D materials. Hybrid MPI plus OpenMP parallelization is implemented to enable efficient calculations on large systems (up to at least 50 atoms) using high-performance computing. Taken together, Perturbo provides efficient and broadly applicable ab initio tools to investigate electron–phonon interactions and carrier dynamics quantitatively in metals, semiconductors, insulators, and 2D materials. Program summaryProgram Title:PerturboCPC Library link to program files:https://doi.org/10.17632/34m2p6v79t.1Developer’s repository link:https://perturbo-code.github.ioLicensing provisions: GNU General Public Licence 3.0Programming language:Fortran, PythonExternal routines/libraries:LAPACK, HDF5, MPI, OpenMP, FFTW, Quantum-ESPRESSO, Wannier90Nature of problem: Computing transport properties from first-principles in materials, including the electrical conductivity, carrier mobility and Seebeck coefficient; Simulating ultrafast nonequilibrium electron dynamics, such as the relaxation of excited carriers via interactions with phonons.Solution method: We implement the first-principles Boltzmann transport equation, which employs materials properties such as the electronic structure, lattice dynamics, and electron–phonon collision terms computed with density functional theory and density functional perturbation theory. The Boltzmann transport equation is solved numerically to compute charge transport and simulate ultrafast carrier dynamics. Wannier interpolation is employed to reduce the computational cost.Additional comments: Hybrid MPI plus OpenMP parallelization is implemented to run large calculations and take advantage of high-performance computing. Most results are output to HDF5 file format, which is portable and convenient for post-processing using high-level languages such as Python and Julia.