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Half-Metallic Ferromagnetism Character in Cr-Doped CaS Diluted Magnetic Insulator and Semiconductor: an Ab Initio Study
摘要： The overall aim of this study is to investigate theoretically the structural, electronic, and magnetic properties of calcium sulfide (CaS) doped with chromium (Cr) impurity, in order to conduct a new search dilute magnetic semiconductors (DMS) suitable for different applications in electronics and spintronics. For measuring, the physical property of this compound is implemented using the first principles approach employed in WIEN2K code. The structural characteristics are optimized using the Generalized Gradient Approximation established by Perdew-Burk-Ernzerhof (PBE-GGA). We calculate and minimize the total energy of the three ternary compounds (Ca0.75Cr0.25S, Ca0.50Cr0.50S, and Ca0.25Cr0.75S) in the paramagnetic (PM), ferromagnetic (FM), and antiferromagnetic (AFM) phase. We find all compounds stable in (FM) structure, whereas the modified Becke and Johnson local density approximation (mBJ-LDA) functional has been employed to evaluate the electronic and magnetic properties. Based on our findings, indicate that this system revealed a half-metallic ferromagnetic behavior with half-metallic gap (HM) and 100% spin-polarized at the fermi level for all chromium (Cr) concentrations. This advantageous set of properties is due to the half-metallic behavior, where the majority spin and minority spin exhibit metallic and semiconducting behaviors respectively. The chromium atom is the most important source of the total magnetic moment in these compounds (4 μβ) by comparison with magnetic moments produced by Ca and S atoms, which have minor contribution. Finally, our prediction results require an experimental confirmation in the future.
关键词： Diluted magnetic insulators (DMI),Spintronics,CaS,HM ferromagnetism,Density functional theory (DFT)
更新于2025-09-10 09:29:36
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High-accuracy large-scale DFT calculations using localized orbitals in complex electronic systems: the case of graphene–metal interfaces
摘要： Over many years, computational simulations based on density functional theory (DFT) have been used extensively to study many different materials at the atomic scale. However, its application is restricted by system size, leaving a number of interesting systems without a high-accuracy quantum description. In this work, we calculate the electronic and structural properties of a graphene–metal system significantly larger than in previous plane-wave calculations with the same accuracy. For this task we use a localised basis set with the Conquest code, both in their primitive, pseudo-atomic orbital form, and using a recent multi-site approach. This multi-site scheme allows us to maintain accuracy while saving computational time and memory requirements, even in our exemplar complex system of graphene grown on Rh(1 1 1) with and without intercalated atomic oxygen. This system offers a rich scenario that will serve as a benchmark, demonstrating that highly accurate simulations in cells with over 3000 atoms are feasible with modest computational resources.
关键词： graphene–metal interface,density functional theory,large-scale simulations,localized orbitals
更新于2025-09-10 09:29:36
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A computational study on linear and bent adsorption of CO2 on different surfaces for its photoreduction
摘要： The adsorption of CO2 on the surface of heterogeneous catalysts is crucial for the subsequent photoreduction reactions. As the direct one-electron reduction of CO2 is extraordinarily difficult because of the –1.9 V reduction potential, adsorption induced CO2 bending to form CO2δ- is considered one efficient approach to decrease the overpotential of the intermediate formation during CO2 reduction. However, it is still unclear what material and surface are in favor of the formation of adsorption-induced bending of CO2, which is important for the design of active surfaces. Here we perform the first principle study on the adsorption of CO2 on the surface of some typical photocatalysts and co-catalysts. It is found that the CO2 bending upon adsorption can only occur on certain crystal surfaces of some materials, even on the perfect surface without any defects. If the exposed crystal surface has a linear metal-oxygen-metal (M-O-M) structure, the carbonate-like configuration upon CO2 adsorption may be easier to be formed than that on the other exposed surfaces. TiO2 (001), CeO2 (111), CeO2 (110) and MgO (100) seem more attractive among all the surfaces under study, as the bent CO2 configuration on these two surfaces are more stable than the linear one. Moreover, the barrier that CO2 changes from linear configuration to bent is relatively small. Our results are in good agreement with the experimental results that TiO2 (001) and MgO (100) exhibit high photocatalytic activity.
关键词： CO2 reduction,Density functional theory,Bent configuration,Adsorption,Linear configuration
更新于2025-09-10 09:29:36
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Structural, vibrational and optical properties of an organic-inorganic hybrid crystal of benzyl 4-aminopyridinium tetrabromocadmate(II) based on DFT calculations
摘要： An organic-inorganic hybrid crystal, [Bz-4-NH2Py]2[CdBr4](1) (Bz-4-NH2Py = 1-benzyl-4'-aminopyridinium), was grown successfully by slow evaporation solution growth method at room temperature and characterized. In tetrachlorocadmate(II) dianion, the CdII ion is coordinated by four Br atoms in a close to tetrahedral geometry. The crystal packing is stabilized by C-H···Br hydrogen bonds between [Bz-4-NH2Py]+ cations and [CdBr4]2- anion forming a three-dimensional network. Powder XRD diffraction study confirms the crystalline nature of the title compound. Thermal stability and the gaseous products of decomposition at 362 oC were examined by TG-DTA-MS technique. The Fourier transform infrared (FT-IR) and Raman spectra were recorded and analyzed with the aid of DFT calculations in order to make a suitable assignment of the observed bands. UV-vis spectral analysis was used to determine the band gap energy, and the nonlinear optical (NLO) effect of the compound was predicted using DFT. Further, the title compound exhibits strong fluorescence emission at 394, 329 and 467 nm in the solid at room temperature.
关键词： Nonlinear optical properties,Tetrabromocadmate(II) dianion,Benzyl 4-aminopyridinium,Density functional theory calculation,Crystal structure
更新于2025-09-10 09:29:36
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The Origin of the π-π Spacing Change upon Doping of Semiconducting Polymers
摘要： While there is agreement about the local structural order of semiconducting polymers such as poly(3-hexylthiophene) (P3HT), there is still debate over the impact of molecular doping. One prevalent interpretation is that dopant molecules intercalate in the π-π stacking of crystallites; however, this idea has recently been challenged. We present here electron diffraction measurements of P3HT doped with the two dopants 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) and molybdenum tris[1-(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene] (Mo(tfd-CO2Me)3), which have considerably different sizes and shapes, processed by different doping techniques. We observe a reduction in the π-π spacing of P3HT upon doping with both dopant molecules and doping techniques. These data are not consistent with both of the dopants intercalating in the π-π stacks and an alternative explanation is, therefore, required to explain these results. Density functional theory calculations for P3HT model oligomers suggest that the polaron delocalizes between adjacent chains and thus leads to attractive forces that reduce the π-π spacing, without the physical presence of any dopant molecules. Our study emphasizes that not only geometric effects induced by dopant molecules lead to the observed reduction of π-π spacing, but the charging itself.
关键词： semiconducting polymers,electron diffraction,π-π spacing,F4TCNQ,Mo(tfd-CO2Me)3,density functional theory,molecular doping,P3HT
更新于2025-09-10 09:29:36
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Structural, elastic, electronic, thermodynamic, and optical properties of layered BaPd2As2 pnictide superconductor: A first principles investigation
摘要： BaPd2As2, belonging to the 122 pnictide group, is an iron-free layered transition metal arsenide which exhibits superconductivity at low temperature when realized in the ThCr2Si2 type structure (I4/mmm). We have performed density functional theory (DFT) based calculations to investigate the structural, elastic, electronic, thermodynamic, and optical properties of BaPd2As2 in this study. The structural, elastic, and the band structure features are compared with the available experimental and theoretical results. Pressure and temperature dependences of various important thermodynamic functions, e.g., bulk modulus, specific heats at constant pressure and volume, coefficient of volume thermal expansion, and Debye temperature are studied in details for the first time. The optical parameters of BaPd2As2 are also studied in details for the first time. The optical properties compliment the electronic band structure characteristics. Optical constants show significant dependence of the state of polarization of the incident electric field. BaPd2As2 exhibits high reflectance in the infrared and near-visible region and strongly absorbs the ultraviolet radiation. The relevance of the electronic energy density of states and the characteristic phonon frequency to superconductivity in BaPd2As2 is also discussed.
关键词： BaPd2As2 superconductor,Density functional theory,Electronic band structure,Optical properties,Elastic constants,Thermodynamic properties
更新于2025-09-10 09:29:36
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Enhancing optical absorption in visible light of ZnO co-doped with europium and promethium by first principles study through modified Becke and Johnson potential scheme
摘要： By using first-principle calculations we studied the electronic, optical and magnetic properties of ZnO co-doped with Eu and Pm. In this calculation, we used Wien2k code based on Full potential linearized augmented plane waves (FP-LAPW) method with the modified Becke-Johnson (mBJ) approximation. This correction gives good band gap compared to experimental band gap. The introduction of Eu and Pm codoping leads to an increase in the band gap. Electrons can transit easily from the valence band to the conduction band, which results in an enhancement of visible light absorption in a wider absorption range. Absorption spectra reach a high value in visible and infrared light regions. With the significance of the obtained results, the studied compounds may potentially find spintronic and optoelectronic applications.
关键词： transmittance,Zinc Oxide,density functional theory,band gap,spintronics,Rare Earth,magnetic properties,absorption,modified Becke-Johnson,photovoltaic
更新于2025-09-10 09:29:36
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Synthesis, crystal growth, structural, spectral, thermal, optical characteristics and density functional theory calculations of a novel third-order nonlinear optical material: 4-acetylanilinium dihydrogen phosphate (4AADP) single crystals
摘要： Single crystals of 4-acetylanilinium dihydrogen phosphate (4AADP), a novel third-order nonlinear optical material has been synthesized and successfully grown by the slow evaporation solution growth technique using acetone as a solvent at room temperature. The single crystal X-ray diffraction analysis implies that 4AADP crystallized into a monoclinic crystal system with the centrosymmetric space group P21/c. The molecular structure of the grown 4AADP compound was evidently established by using 1H and 13C NMR spectral analysis. The vibrational behavior of the chemical bond and discrete functional groups of the grown crystal were identified using FT-IR and FT-Raman spectral analysis. UV-Visible-Near Infrared spectral analysis shows that the grown crystal was highly transparent in the entire visible range above 365 nm. The 4AADP compound was thermally stable up to 195 oC and it was ascertained by thermogravimetric and differential scanning calorimetric analysis. The photoactive behavior of the material was established from photoluminescence studies. The ionization energy (I) and electron affinity (A) were computed from the energy gap values of HOMO and LUMO orbitals respectively. The Molecular electrostatic potentials and Mulliken charges have also been calculated theoretically by applying DFT/B3LYP method. The nonlinear absorption coefficient (β), third order nonlinear refractive index (n2) and third-order nonlinear optical susceptibility (χ3) were calculated from Z-scan measurements, reveals that the grown crystal of 4AADP could serve as a promising source for nonlinear optical devices.
关键词： Crystal growth,Density functional theory,Z-scan,Thermal analysis,Spectral studies
更新于2025-09-10 09:29:36
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Frequency dependent linear and nonlinear optical properties of compositionally tuned inorganic CsSnX (X = Br, I) composites
摘要： Structural, electronic and optical properties of CsSnX (X = Br, I) system have been thoroughly investigated by means of an unbiased crystal structure screening, density functional theory and perturbation approach. Crystallography of known parent structures, CsI and CsBr were well replicated compared to experimental observations. Experimentally verified cubic Cs2SnI6 phase was operatively reproduced. Its computed crystal class and simulated XRD pattern match the available experimental data, hence signifying the robustness of methodology applied. Other energetically and dynamically stable structures include cubic Cs2SnBr6, triclinic Cs2Sn2Br6 and Cs2Sn2I6. These phases are direct semiconductors which exhibit non-monotonic association between GW corrected band gap and halogen type or atomic mass. Instead, their energy gap is determined by the structure of CsSn halide compounds, and span an energy range from mid infrared to near ultraviolet region. The GW-raised gap was incorporated as scissor shift to ensure good reliability of optical calculations. Dynamical dielectric function, adsorption coefficient, energy-loss and refractive index spectrum of aforementioned phases were acquired. Both novel Cs2Sn2Br6 and Cs2Sn2I6 phases have impressive zero limit second-order susceptibility ranging from 3.1 pm V-1 to 22.8 pm V-1.
关键词： Ab initio,Optical Properties,Stable phases,Density functional theory
更新于2025-09-10 09:29:36
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The electronic structure and magnetic property of the Mn doped β-Ga2O3
摘要： Ga2O3 is a promising candidate for high power, high voltage devices. In this work, the band structure of the pure β-Ga2O3 and the impact of orbital coupling on the Mn doped β-Ga2O3 electronic structure are analyzed based on density functional theory. The Mn dopant induces impurity bands near the band edge, resulting in the decrease of the band gap of the Ga2O3. When the Mn dopants only substitute the octahedrally coordinated Ga atoms, the doped systems possess the most stable structure and the ferromagnetism, the Monte Carlo simulation predicts that the Curie temperature is 421K. The room temperature ferromagnetism can be ascribed to the strong p-d coupling and the delocalization of O-2p orbital. The oxygen vacancy and gallium vacancy can induce the deep donor level and acceptor level into the band gap, respectively. Due to the valence change of Mn dopant, the Mn dopant undergoes a transition from donor to acceptor when the substrate obtains more carriers. Our results not only explain the observed electronic and magnetic properties in experiment, but also provide a theoretical model for designing high performance Ga2O3 based devices.
关键词： β-Ga2O3,Density Functional Theory,Electronic Structure,Ferromagnetism
更新于2025-09-10 09:29:36