Ultrasoft Pseudopotential Plane Wave Research Articles

Computational investigation on physical properties of lead based perovskite RPbBr3 (R = Cs, Hg, and Ga) materials for photovoltaic applications

In the modern era, the major problem is solving energy production and consumption. For this purpose, perovskite materials meet these issues and fulfill energy production at a low cost. Density functional theory and the Cambridge Serial Total Energy Package (CASTEP) are used to examine the characteristics of the cubic inorganic perovskites RPbBr3 (R = Cs, Hg, and Ga). In the context of the generalized gradient approximation (GGA), the ultrasoft pseudo-potential plane wave technique and the Perdew–Burke–Ernzerhof exchange–correlation functional are used for investigations. Structural, mechanical, electronics, and optical properties are investigated using CASTEP code. According to structural properties, compounds have a cubic nature with space 221 (Pm3m). Compounds formation energy (− 3.46, − 2.21, and − 3.14 eV)of (CsPbBr3, HgPbBr3, and GaPbBr3) and phonon calculations are studied and find that compounds are stable. The results of our investigation show that the compounds have narrow bandgaps of direct kind, with 1.85 eV for CsPbBr3, 1.56 eV for HgPbBr3, and 1.71 eV for GaPbBr3, respectively, indicating that they may be used to improve conductivity. Additionally, anisotropy (2.135, 3.651, 10.602), Pugh’s ratio (1.87, 2.25, 2.14), and Poison’s ratio (0.27, 0.31, 0.29) are traits that the compounds (CsPbBr3, HgPbBr3, GaPbBr3) display a ductile nature. The CsPbBr3 compound showed significant optical conductivity and absorption in terms of their optical properties, especially in the visible region, which makes them suitable for use in solar cell applications as well as for LED applications.

First-principles study of the effects of Li/Na/K doping and point defects on the magnetic and photocatalytic properties of monolayer GaN (0 0 1)

In the experimental preparation of monolayer GaN (0 0 1) by chemical-vapor deposition, H impurities inevitably remain, and the intrinsic defect VGa inevitably forms. In this research, generalized gradient approximation + U plane-wave ultrasoft pseudopotentials are computed using the density-functional theory framework. The effects of Li/Na/K doping and point defect (Hi-VGa) coexistence on the magnetic properties and photocatalytic properties of monolayer GaN (0 0 1) surfaces are investigated. Results show that the monolayer Ga34MN36 (M = Li/Na/K) (0 0 1) surfaces are magnetic, and the source of its magnetism is primarily the itinerant electrons of N2− ions. The monolayer Ga34MHiN36 (0 0 1) surfaces are relatively more stable, and the separation degree of carriers is better than the monolayer Ga34MN36 (0 0 1) surfaces. In particular, the monolayer Ga34LiHiN36 (0 0 1) surface has a large electric-dipole moment, strong carrier activity, strong absorption efficiency, and strong oxidation-reduction properties. Therefore, the monolayer Ga34LiHiN36 (0 0 1) surface is the most suitable photocatalyst.

First-principles study of the magnetic and optical properties of PtSe2 doped with halogen elements F, Cl, and Br

The electronic structure, magnetic and optical properties of halogen-doped two dimensional PtSe2 are investigated by using the first-principles ultra-soft pseudopotential plane wave method based on density functional theory. It is shown that the doped PtSe2 is more stable under Bottom-Se conditions than under Top-Se conditions, and the higher the doping concentration (C d), the lower the band gap. At C d = 5.56%, the Cl- and Br-doped PtSe2 are transformed from a non-magnetic semiconductor to a magnetic n-type semiconductor with a magnetic moment (M B) of 1 μB; while neither the F-doped PtSe2 nor the pristine PtSe2 is magnetic. When C d = 11.1%, the F-doped PtSe2 at the first neighborhood becomes magnetic metal with M B = 1.39 μB; while that doped at the second nearest neighbor retains a semiconductor with M B = 0. Thus Cl- and Br-doped PtSe2, as well as the first-neighbor F-doped PtSe2 can be well applied in spintronic devices. The optical properties are enhanced for all three doping systems with an obvious peak appearing in the infrared light region. Absorption and reflectivity curve still has a peak in the infrared light region.

A DFT study of structural, electronic, optical, thermal and mechanical properties of cubic perovskite KGeX3 (X = Cl, Br) compound for solar cell applications

This study examined the structural, electronic, optical, mechanical, and thermal properties of K-based halide perovskites KGeX3 (X = Cl, Br). All the calculations have been carried out using the DFT-based CASTEP simulation package with an ultra-soft pseudo-potential plane wave and PBE-GGA technique. Both the studied perovskite compounds are stable in terms of mechanical and thermal stability. The calculated electronic properties indicate that both materials have a semiconducting behavior with a direct band gap. The band gap value is 0.92 and 0.62 eV for KGeCl3 and KGeBr3, respectively. The analysis of the electronic properties reveals a notable reduction in the bandgap as chlorine (Cl) is substituted with bromine (Br), decreasing from 0.92 to 0.52 eV. The results of our calculations are in good agreement with the previously reported research. The optical properties analysis reveals that both materials demonstrate high absorption and minimal reflection within the visible spectrum. The determined values for Poisson’s and Pugh’s ratios suggest that studied materials demonstrate a ductile behavior. The obtained values of Debye temperature are 265.25 and 191.62 K for KGeCl3 and KGeBr3, respectively. Based on their appropriate direct band gap and high absorption coefficient, these materials are considered promising candidates for photovoltaic applications, and are proposed as ideal potential materials for solar cells applications.

First principle investigation of tungsten based cubic oxide perovskite materials for superconducting applications: A DFT study

Perovskite will play an important role in the materials study to investigate the different properties. The CASTEP (Cambridge Serial Total Energy Package) code will be used to investigate the material properties. The structural, electronic, thermodynamic, and optical characteristics of novel tungsten-based oxide-perovskite materials WXO3 (where X = Cr and Hg) were investigated by using first principle calculations (CASTEP) with ultra-soft pseudo-potential PW (plane wave) and GGA (generalized gradient approaches)-PBE (Perdew-Burke-Ernzerhof) exchange correlation-functional. According to the calculations, both compounds have a space group of PM3m with a cubic structure. The results we discovered are entirely novel compounds, as demonstrated by computations. According to calculations, the band structure of WXO3 has a zero band gap. The graphical interpretations like DOS (density-of-states), partial DOS, and band structure in both perovskite materials reveal conclusive proof of conductive behavior. The presence of ionic bonds is revealed by a study of bonding characteristics shown by Poisson's ratios of 0.71 and 0.49 for WCrO3 and WHgO3, respectively. The WCrO3 and WHgO3 optical characteristics have also been studied and assessed. The Fermi level will be so highly overlapped that most of the electrons will lie from the conducting valence band VB to the conduction band CB and vice versa. Thermodynamic characteristics are studied, like Debye temperature, sound velocity, melting temperature, and compressibility. These compounds are extensively used in medical devices, sensitive devices, computer parts, and storage systems. Further investigation will be required on these materials with doping any element to enhance the band gap to study the other properties like photocatalytic and solar cell applications.

Structural, Electronic, Dynamic, and Optical Properties of 2D Monolayer Tungsten Telluride (2H-WTe2) under Small Biaxial Strain Using Density Functional Theory (DFT and DFT + U)

The structural, electronic, vibrational, and optical properties of 2D- 2H-WTe2 monolayer are investigated using density functional theory with respect to a plane wave ultrasoft pseudopotentials (PW-USPPs) in a generalized gradient approximation (GGA) and with the Hubbard potential (GGA + U). The equilibrium state properties such as lattice parameters, unit cell volume, bulk modulus, and its derivative are determined. The band gap values of monolayer 2H-WTe2 are investigated for unstrained, 2% biaxial compression, and biaxial tensile stress using GGA, respectively. The obtained band gap values of 2H-WTe2 with respect to GGA are 1.043, 1.1487, and 0.9439 eV for unstrained, biaxial compression, and tensile strain, respectively. Moreover, the band gap values determined using Hubbard correction (GGA + U) are 1.1089 eV (unstrained), 1.2332 eV (2% biaxial compression), and 0.9945 eV (2% biaxial tensile stress), respectively. The band gap value obtained using Hubbard correction predicts the experimental value more precisely. The projected density of state shows W (3d) orbital is more dominant both in the valence band maximum and conduction band minimum. Moreover, a small amount of tensile or compressive strain is used to tune the band gap of the monolayer without affecting its direct band gap nature. In addition to this, the phonon dispersion and optical properties are discussed for tensile strain, unstrained, and compressive strain, respectively.

First-principles study on the magnetism, carrier activity, and carrier lifetime of Ga2O3: Li or Na or K with different valence Ga vacancies and H interstitial

A first-principles study is conducted by using the generalized gradient approximation within the framework of density functional theory, with the plane wave ultrasoft pseudopotential + U method. We investigate the effects of formation energy, magnetism, and photocatalytic performance in Ga30MO48 (VGa0/VGa1−/VGa2−/VGa3−, M = Li or Na or K) and Ga30MHiO48 (VGa0/VGa1−/VGa2−/VGa3−) systems. Results indicate that under O-rich conditions, the formation energy (Ef) is lower, making the systems more stable and easily doped. The Ga30MHiO48 (VGa0/VGa1−/VGa2−/VGa3−) system exhibits a relatively lower Ef than Ga30MO48 (VGa0/VGa1−/VGa2−/VGa3−). The magnetic source of the doping systems is primarily contributed by O1− ions near Ga vacancies. The Ga30KHiO48 (VGa1−) system exhibits good carrier activity, the longest electron–hole lifetime, noticeable light absorption, and strong reduction capability, making it a promising photocatalyst for H2 production.

The study of structural, electronic, and optical properties of Ti- substituted CaZr1-xTix S3 (x=0.00, 0.25, 0.50, 0.75, and 1.00) for optoelectronic applications: Using GGA and GGA+U

In this study, we examined an orthorhombic phase, CaZr1−xTixS3(x = 0.00, 0.25, 0.50, 0.75, 1.00) (space group Pnma (62)) with B-site Zr substituted by Ti (25%Ti, 50%Ti, 75%Ti) using density functional theory, with the help of a plane wave ultra-soft Pseudopotentials (PW-USPPs) in a generalized gradient approximation (GGA) and with Hubbard onsite correction (DFT + U). The equilibrium state properties such as lattice parameters, unit cell volume, bulk modulus, and its derivative are calculated. The change in concentration of Ti affects the bulk modulus and its derivatives which results in variations in the compressibility and hardness of the material. It is found that CaZr1−xTixS3 with different concentrations of Ti shows a tuned direct band gap located at Γ-symmetry point. The band gap values decrease as impurity concentration increases. The band gap values of CaZr1−xTixS3 (for 0.25, 0.50, 0.75, and 1.00) lie in the optimal energy range (1.0–1.6 eV). Moreover, it is observed that CaZr1−xTixS3(x = 0.00, 0.25, 0.50, 0.75, 1.00) has a good optical response from the visible to ultraviolet energy range. The results predict these materials may be used in solar cell applications and optoelectronic devices.

First-principles calculations to investigate structural, electronic, elastic, optical and transport properties of halide double perovskites Cs2ABF6 (AB = BiAu, AgIr, CuBi, GaAu, InAs, InAg, InAu, InSb and InBi) for solar cells and renewable energy applications

The first-principles calculations are used for a comprehensive study of the novel halide double perovskites by using the CASTEP code which is based on DFT. The correlational function of the GGA-PBE with the ultra-soft pseudo potential USP plane wave was utilized to carry out the present study. For all novel halide double perovskites, the lattice parameters were determined first, and the compounds were subjected to the mechanical stability criteria. From 0.56 to 4.99 eV, the Cs2ABF6 materials are found to be direct band-gaps. The dielectric functions of the materials of interest are large near and in the middle ultraviolet regions. They become smaller in the far and extreme ultraviolet regions. Furthermore, the Cs2ABF6 are found to be elastically stable, ductile, anisotropic and relatively low hard materials. A comprehensive analysis of the optoelectronics and thermoelectric nature with a given band gaps are carried out. This reflects the use of Cs2ABF6 in solar cells, energy storage devices, photovoltaic devices, radiation detectors, photonic crystals, light emitting diodes and thermoelectric generators. Thermoelectric coefficients such as the figure of merit thermal and electrical conductivities, Seebeck coefficient (S), and are also examined to check the possibility of these materials in the field of thermoelectric. The computed value of ZT reflects (ZT ∼ 1) Cs2ABF6 materials and reveals that such type of materials holds a virtuous route toward thermoelectric applicability.

Screening of ABF3 fluoroperovskites by using first-principles calculations

The CASTEP code based on DFT is used to investigate the fluoroperovskites with the general formula ABF3. The correlational function of the GGA-PBE with the ultra-soft pseudo potential USP plane wave was utilized to carry out the present study. For all fluoroperovskites, the lattice parameters were determined first, and the compounds were subjected to the mechanical stability criteria. The B/G ratio was utilized to determine the ductility or brittleness in the stable compounds. Then, the Poisson's ratio was used to verify the ductileness in the stable compounds. The Debye temperature and Cauchy pressure were also determined accordingly. The electronic properties were studied for the compounds which were proved ductile according to the Pugh's criteria and Poisson's ratio. Among the ductile compounds, CdSbF3 was found to have a band gap of 0.257 eV while zero band gap was found in all the other compounds. All the other materials possess the metallic nature due to having zero band gap. As a result of its semiconducting nature, CdSbF3 is found to be the best material for various applications.

Analysis of XGaO3 (X = Ba and Cs) cubic based perovskite materials for photocatalytic water splitting applications: a DFT study

Energy conversion has become an important technology for meeting energy production and consumption in the modern era. Water splitting and solar cell technologies are projected to close the gap between demand and consumption. Therefore, XGaO3 (X = Ba and Cs) compounds having characteristics i.e., electrical, optical, mechanical, and structural are depicted by using a density functional theory (DFT) based CASTEP software with ultrasoft pseudo-potential plane-wave and Generalized Gradient Approximation and Perdew Burke Ernzerhof exchange correlation functional (GGA-PBE). According to the findings, all of these compounds have a cubic “pm3m” structure with space group 221. The CsGaO3 and BaGaO3 have direct and indirect band gaps, with respect to electronic band-structure recreations. Density of states like total density of states (TDOS) and partial density of states (PDOS) commend the extent of localization of electrons in numerous bands. The optical properties of these compounds are explored by adjusting dispersion curve/relation for theoretical dielectric function (DF) scale to the corresponding peaks. As a result, these materials could be used to consume light in the visible zone via photo catalysis. CsGaO3 in combination with BaGaO3 can produce effective results, so these compounds have a remarkable potential application for sensing and water splitting.

The First-Principles Investigation of Structural Stability, Mechanical, Vibrational, Thermodynamic, and Optical Properties of CaHfS3 for Optoelectronic Application

In this study, the structural, electronic, elastic, phonon vibration, thermodynamic features, and optical properties of the orthorhombic phase of (space group Pnma) C a H f S 3 were examined by first-principles calculations utilizing the plane wave ultrasoft pseudopotentials in generalized gradient approximations (GGAs) and with Hubbard on-site correction (DFT + U). To improve the value of the band gap, the exchange correlation potential is also approximated with Hubbard correction (GGA + U). The equilibrium state properties such as lattice parameters, unit cell volume, bulk modulus, and its derivative were calculated and are in good agreement with the existing data. The mechanical properties such as bulk modulus, shear modulus, Young’s modulus, and elastic anisotropy were determined from the obtained elastic constants. The ratio of bulk modulus to shear modulus confirms that the orthorhombic phase of C a H f S 3 is a ductile material. In addition, the longitudinal sound velocity, transverse sound velocity, and Debye temperature for C a H f S 3 have been computed. The absence of negative frequencies in the phonon dispersion curve and the phonon density of states confirm that C a H f S 3 in the orthorhombic phase is dynamically stable. The thermodynamic parameters such as free energy, entropy, and heat capacity were examined with variations in temperature. Finally, the absorption coefficient, dielectric constant, energy loss function, reflectivity, and refractive index are discussed in detail in the spectral range 0–1.6 Ry (21.77 eV). The polarizations along (100), (010), and (001) directions significantly show different optical responses.

Lithium-based perovskites materials for photovoltaic solar cell and protective rays window applications: a first-principle calculations

Perovskites are the key enabler materials for the solar cell applications in the achievement of high performance and low production costs. In this article, the structural, mechanical, electronic, and optical properties of rubidium-based cubic nature perovskite LiHfO3 and LiZnO3 are investigated. These properties are investigated using density-functional theory with the aid of CASTEP software by introducing ultrasoft pseudo-potential plane-wave (USPPPW) and GG-approximation-PB-Ernzerhof exchange–correlation functionals. It is investigated that the proposed compounds exhibit stable cubic phase and meet the criteria of mechanical stability by the estimated elastic properties. Also, according to Pugh's criterion, it is noted that LiHfO3 is ductile and LiZnO3 is brittle. Furthermore, the electronic band structure investigation of LiHfO3 and LiZnO3 shows that they have indirect bandgap (BG). Moreover, the BG analysis of the proposed materials shows that these are easily accessible. Also, the results for partial density of states (DOS) and total DOS confirm the degree of a localized electron in the distinct band. In addition, the optical transitions in the compounds are examined by fitting the damping ratio for the notional dielectric functions scaling to the appropriate peaks. At absolute zero temperature, the materials are observed as semiconductors. Therefore, it is evident from the analysis that the proposed compounds are excellent candidates for solar cells and protective rays applications.

First-principles calculations to investigate structural, electronic, elastic and optical properties of radium based cubic fluoro-perovskite materials

Perovskite materials play a vital role in the field of material science via experimental as well as theoretical calculations. Radium semiconductor materials are considered the backbone of medical fields. These materials are considered in high technological fields to be used as controlling the decay ability. In this study, radium-based cubic fluoro-perovskite XRaF3 (where X = Rb and Na) are calculated using a DFT (density functional theory). These compounds are cubic nature with 221 space groups that construct on CASTEP (Cambridge-serial-total-energy-package) software with ultra-soft PPPW (pseudo-potential plane-wave) and GGA (Generalized-Gradient-approximation)-PBE (Perdew-Burke-Ernzerhof) exchange-correlation functional. The structural, optical, electronic, and mechanical properties of the compounds are calculated. According to the structural properties, NaRaF3 and RbRaF3 have a direct bandgap with 3.10eV and 4.187eV of NaRaF3 and RbRaF3, respectively. Total density of states (DOS) and partial density of states (PDOS) provide confirmation to the degree of electrons localized in distinct bands. NaRaF3 material is semiconductors and RbRaF3 is insulator, according to electronic results. The imaginary element dispersion of the dielectric function reveals its wide variety of energy transparency. In both compounds, the optical transitions are examined by fitting the damping ratio for the notional dielectric function scaling to the appropriate peaks. The absorption and the conductivity of NaRaF3 compound is better than the RbRaF3 compound which make it suitable for the solar cell applications increasing the efficiency and work function. We observed that both compounds are mechanically stable with cubic structure. The criteria for the mechanical stability of compounds are also met by the estimated elastic results. These compounds have potential application in field of solar cell and medical. ObjectivesThe band gap, absorption and the conductivity are necessary conditions for potential applications. Here, literature was reviewed to check computational translational insight into the relationships between absorption and conductivity for solar cell and medical applications of novel RbRaF3 and NaRaF3 compounds.

Structural, electronic, optical and mechanical properties of oxide-based perovskite ABO3 (A = Cu, Nd and B = Sn, Sc): A DFT study

The structural, electronic, optical and mechanical properties for oxide-based cubic perovskites ABO3 (A ​= ​Nd, Cu and B= Sc, Sn) were investigated employing density functional theory (DFT) within the CASTEP (Cambridge Serial Total Energy Package) code, based on ultra-soft pseudo-potential (USP) plane wave and Perdew Burke Ernzerhof (PBE) exchange-correlation functional of Generalized Gradient Approximation (GGA) and Local Density Approximation (LDA). The structural results showed that all compounds are stable. The computed elastic constants also meet the requirements of mechanical stability, hardness, ductile/brittle and bonding nature of materials. All the compounds have anisotropic nature. The electronic band structure calculations show that CuScO3 and CuSnO3 compounds have indirect band gap nature. NdScO3 compound has a direct band gap and NdSnO3 compounds show metallic behavior. All the compounds were identified as semiconductors, except NdSnO3 compounds. The band gap values were in the best agreement with the information that is already available. Partial density of states (PDOS) and total density of states (TDOS) were employed to measure the degree of localized electrons in different bands. The optical transition in the compounds was computed by fitting the dispersion relation of the imagined component. Optical properties showed that these compounds were excellent absorbers of incident radiation. Therefore, it may be assumed that these compounds could be in employment in optoelectronics to capture the ultraviolet range of solar radiations.

The effect of stress on electronic structure and optical properties of CeO2

The effect of stress on the electronic structure and optical properties of CeO2 is studied using the ultrasoft pseudopotential plane wave method based on density functional theory. The results show that the band gap decreases quasi-linearly with the negative stress increasing and increases quasi-linearly with the increase of positive stress. Combining with the density of states (DOS) analysis, the main reason for the change of the band gap is Ce 4f electrons are significantly affected by the stress. When the stress changes from −25 to 30 GPa, the DOS of Ce 4f is far away from the Fermi level and gradually decreases. The influence of stress on optical properties mainly shows two obvious features. The first feature is that the optical properties are gradually appeared as the stress changes from −25 to 30 GPa and the optical edges are moved to high energy direction, in the energy range of 0–3 eV. Another feature is that there is an obvious peak value under the stress of −25–0 GPa, but does not significantly change under the stress of 0–30 GPa, in the energy range of 3–6 eV. The results show that the negative stress enhances the electronic transition, which is beneficial to improve the utilization of light.

First-principles calculations to investigate “H” and “K” doped RbSrF3 for photovoltaic applications

A cubic perovskite RbSrF3 structure has been doped with hydrogen and potassium, and their comparative study was carried out for the structural, electronic, and optical parameters. Self-consistent computation of ultra-soft pseudopotential plane-wave along with generalized gradient approximation (GGA) with Perdew Burke Ehrenzorf (GGA-PBE) exchange-correlation potential under the first principle is used for the computation of properties. Evaluated optimized lattice constant for Pm3m supercell is in good agreement with the already reported results and the bandgap reduces to a desired value for the “K” and “H” doping concentrations from 0% to 0.55%, this reduction is useful for water splitting and photovoltaic applications. The localized electrons for different bands are explained by DOS and PDOS. The optical properties for pure and H, K doped RbSrF3 have been recognized by allocating the maximas obtained after calculations. This was the first-ever comparative theoretical study of this type for RbSrF3 compound with the potassium and hydrogen dopants as far as our knowledge.

First-principles calculations to investigate the effect of Cs-doping in BaTiO3 for water-splitting application

The structural, electronic, and optical properties of the pure and Cs-doped BaTiO3 are investigated theoretically with the help of Cambridge Serial Total Energy Package code, which utilizes an ultra-soft pseudopotential plane wave and a Perdew Burke Ernzerhof exchange-correlation functional of the Generalized Gradient Approximation. The DFT + U approximation is employed to get the better results for electronic properties. The calculated lattice parameters and bandgap for pure BaTiO3 are found 4.034 Å and 2.513 eV which are consistent with the previous studies. The pure BaTiO3 possesses an indirect while the Cs-doped BaTiO3 systems have a direct band gap. The value of band gap is found 1.858, 2.103 and 1.882 eV for 0.13, 0.26 and 0.39% Cs-doped BaTiO3, respectively. For pure BaTiO3, the absorption edge is in the invisible region, whereas, the Cs-doped (0.13%) BaTiO3 possesses the maximum absorption edge in the visible region. By introducing the new Cs-3p states into the valence band of BaTiO3, the photocatalytic activity of the material is enhanced. For 0.26 and 0.39% Cs-doped BaTiO3, the absorption edge in the visible region is found lower than that of 0.13% Cs-doped BaTiO3. Moreover, 0.13% Cs-doped BaTiO3 possesses a minimal energy loss than that of 0.26 and 0.39% Cs-doped BaTiO3. Therefore, 0.13% Cs-doped BaTiO3 is found an efficient candidate for photocatalytic water-splitting by studying the combined effect of electronic and optical properties.

First-principles calculations to investigate variation in the bandgap of NaSrF3 Fluoro-Perovskite with external static isotropic pressure and its Impact on optical properties

The theoretical investigation of NaSrF3 fluoro-perovskite is carried out using ultra-soft pseudo-potential USP plane wave and Perdew Burke Ernzerhof (PBE) exchange–correlation functional of Generalized Gradient Approximation (GGA) with the help of the density functional theory-based Cambridge Serial Total Energy Package (CASTEP) code. All the properties are investigated under the effect of external static isotropic pressure ranging from 0 to 100 GPa and 300 GPa. The lattice parameters of the material are decreased with the increment of the external pressure. The value of band gap is found 4.328, 2.795, and 0 eV at 0, 100 and 300 GPa, respectively. The optical properties of the material i.e., absorption, reflectivity, dielectric function, refractive index, conductivity, and loss function are also investigated. The static values of ε1 (ω) and n (ω) increase with the increase in pressure. It is resulted from the optical properties that the material has a high refractive index, absorption, and conductivity, and thus it is applicable in different photovoltaic systems like data storage media, and photonic crystals. Furthermore, the electronic properties of the material indicate that it operates as a semiconductor at 0 to 100 GPa while it acts as a conductor at 300 GPa.

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

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