Energy Band Calculations Research Articles

DFT Analysis of Transition Metal (TM) Substitutions on Cu‐Based Chalcogenides: Structural, Electronic, and Thermophysical Properties for Interface Thermal Performance and Energy

ABSTRACTThe current investigation employs first‐principles DFT (density functional theory) calculations to examine the influence of transition metal replacements on the structural, thermodynamic, and thermoelectric properties of Cu‐based chalcogenides TMCu3Se4 (TM = Nb/Ta/V). The PBE‐generalized gradient approximation (GGA) model is utilized to compute the fundamental properties of Cu‐based chalcogenides under study. A thorough examination of the energy band structures indicates that these chalcogenides are semiconductor compounds with indirect energy bandgaps. We can infer from the calculated energy band structures that the bandgap values are 1.67, 1.77, and 1.05 eV for NbCu3Se4, TaCu3Se4, and VCu3Se4, respectively. The values for NbCu3Se4, TaCu3Se4, and VCu3Se4 are 0.661, 0.998, and 0.996, respectively. These values make them highly appropriate for usage in thermoelectric (TE) devices. The thermoelectric characteristics of pyrochlore oxides TMCu3Se4 (TM = Nb/Ta/V) suggest that these materials have promising potential for energy‐related applications. The analyzed thermodynamic properties demonstrate that the Cu0based chalcogenide materials TMCu3Se4 (TM = Nb/Ta/V) exhibit a notable level of thermal stability.

Enhanced catalytic activity of modified g-C3N4 heterojunction for photocatalytic degradation of methylene blue from wastewater

Rapid recombination of photoinduced charge carriers and poor photocatalytic degradation performance greatly hinder the large-scale application of g-C3N4 photocatalysis. Therefore, the g-C3N4 is modified by BiPO4 to overcome its poor photocatalytic performance, which is investigated by methylene blue (MB) removal. The S scheme heterojunction is constructed by modifying g-C3N4 with BiPO4, which can effectively preserve the redox activities of holes and electrons on VB and CB, exhibiting good photocatalytic activity. Therefore, the modified g-C3N4 exhibits excellent photocatalytic activity with efficient separation of the photoelectron-hole, compared to pure g-C3N4 and BiPO4. The modified g-C3N4 exhibits large MB degradation removal of 96.7 %, which is significantly larger than the pure g-C3N4 (46.3 %) and BiPO4 (3.3 %) owe to synergy, respectively. The photodegradation rate constant of the modified g-C3N4 is 4.8 and 43 times larger than that of the pure g-C3N4 and BiPO4, respectively. The modified g-C3N4 still has large MB removal of 92.9 % after 5 cycles, indicating excellent stability and recyclability. The fractal density calculation of the modified g-C3N4 is investigated combined with LUMO and HOMO analysis. The MB photocatalytic degradation process follows the S scheme charge transfer mechanism, based on degradation mechanism analysis combined with semiconductor energy band and density functional theory calculation analysis. The MB photocatalytic degradation path is systemically analyzed based on MS-UPLC result analysis, which indicates that MB is finally decomposed into CO2 and H2O, achieving the degradation of MB.

Multiwavelength Emission of the Gamma-Ray Burst Prompt Phase. I. Time-resolved and Time-integrated Polarizations

The time-integrated polarization degree (PD) in the prompt optical band of a gamma-ray burst (GRB) was predicted to be less than 20%, while the time-resolved one can reach as high as 75% in the photosphere model. Polarizations in the optical band during the GRB prompt phase have not previously been studied in the framework of the magnetic reconnection model. Here, a three-segment power law of the energy spectrum is used to reconstruct the Stokes parameters of the magnetic reconnection model. Multiwavelength light curves and polarization curves from the optical band to MeV gamma rays in the GRB prompt phase are studied. We found that, depending mainly on the jet dynamics, there is a long-lasting high-PD phase in all calculated energy bands for the typical parameter sets. The time-resolved PD could be as high as 50%, while the time-integrated one is roughly 17% in the optical band. The time-resolved PD in X-rays can reach 60% and the time-integrated one is around 30%–40%. The evolution of polarization angle (PA) is random in both optical and gamma-ray bands for the photosphere model, while it is roughly constant in the synchrotron models. Therefore, future time-resolved PA observations in the prompt optical or gamma-ray band could distinguish between the photosphere and synchrotron models.

Diethylbenzene and ethyltoluene adsorption studies on novel beta antimonide phosphorus nanosheets-a first-principle study.

In the present work, we examined the sensing behavior of monolayer beta antimonide phosphorus (β-SbP) sheets towards toxic volatile organic compounds (VOCs) namely, 1,2-diethylbenzene and 2-ethyltoluene using density functional theory (DFT) method. At first, using cohesive energy structural stability of the monolayer β-SbP is confirmed. The calculated energy band gap value of monolayer β-SbP is 2.168eV, which is a semiconductor. Furthermore, the adsorption properties of 1,2-diethylbenzene and 2-ethyltoluene on β-SbP are studied through key factors, such as adsorption energy, Mulliken charge transfer, and relative band gap variation. The adsorption energy clearly shows (- 0.335 to - 0.903eV) that both 1,2-diethylbenzene and 2-ethyltoluene are physisorbed on β-SbP monolayer. Besides, Mulliken charge transfer falls in the range of - 0.465 to 0.933 e; this information clearly shows that the β-SbP monolayer is a potential candidate for sensing 1,2-diethylbenzene and 2-ethyltoluene molecules. The structural firmness including electronic and adsorption properties of 1,2-diethylbenzene and 2-ethyltoluene on β-SbP monolayer are investigated with the support of the DFT method. Particularly, the hybrid generalized gradient approximation (hybrid GGA) along with Beck's three-parameter + Lee-Yang-Parr (B3LYP) exchange-correlation functional is utilized for relaxing the β-SbP monolayer. In the present work, all calculations are performed using the Quantum Atomistic Tool Kit (ATK) simulation package. In the present work, we utilized β-SbP monolayer as a chief sensing element to detect 1,2-diethylbenzene and 2-ethyltoluene to safeguard humans from toxic environments.

Optical, structural, and electrical performance of CsPbIBr2 perovskites with zirconium doping and bilayer ETLs

This work studies the optoelectronic, and structural characteristics of CsPbIBr2 perovskite solar cells (PSCs) improved by 4 % Zirconium (Zr) doping and a bilayer electron transport layers (ETLs) composed of TiO2 and Zr-doped WO3. X-ray diffraction (XRD) examination of pure and Zr-doped CsPbIBr2 films revealed increased crystal size (39.2–41.2 nm) and lowered lattice constant following Zr doping, suggesting better crystallinity. The calculated energy band gap of pristine and Zr-doped CsPbIBr2 film decreases (1.986–1.926 eV), which improves the light absorption efficiency, while the increase in the refractive index implies that light is slowed down more as it passes through the material, which increases light trapping and absorption within the material. The XRD of Zr-WO3 ETL indicated a monoclinic crystal structure and increased lattice constant, allowing charge carrier transmission. Raman spectroscopy confirms the structural integrity of Zr-WO3. UV–Vis absorption spectra suggest enhanced absorption in the visible region and higher bandgap compared to Zr-doped CsPbIBr2. J-V tests reveal an efficiency rise from 8.54 % to 10.20 % with the proposed of double ETLs, exhibiting substantial breakthroughs in PSCs performance.

Nonlinear Optical Effects of Hybrid Antimony(III) Halides Induced by Stereoactive 5s2 Lone Pairs and Trimethylammonium Cations.

Organic-inorganic hybrid metal halides have unique optical and electronic properties, which are advantageous in the study of nonlinear optical materials. To investigate the effect of stereoactive lone pair electrons and the induction of organic cations on the structure of hybrid antimony(III) halides on nonlinear optics, we synthesize two noncentrosymmetric hybrid antimony(III)-based halide single crystals (TMA)3Sb2X9 (TMA = NH(CH3)3+, X = Cl, Br) by a room-temperature slow evaporation method, and their single-crystal structures, phase transition, X-ray photoelectron spectroscopy, and energy-band structure calculations are studied. More importantly, second-harmonic generation results of (TMA)3Sb2X9 (X = Cl, Br) are about 0.7 and 0.8 × KH2PO4(KDP), respectively. Interestingly, (TMA)3Sb2Cl9 single crystals undergo a reversible structural transition from Pc (No. 7) at room temperature to P21/c (No. 14) at 400 K, while the (TMA)3Sb2Br9 single crystals belong to the noncentrosymmetric space group R3c (No. 161), which clarifies the previous results. This work not only deepens the understanding of the role in lone pair electrons and organic cations in the structural induction in antimony-based halide perovskite materials but also provides guidance for subsequent nonlinear optical explorations.

A new type of two-dimensional piezoelectric material: MOene based on Ti2O and its Janus structure

Two-dimensional (2D) piezoelectric materials have been widely studied because of their broad application prospects. In this paper, the piezoelectric properties of a MXene-like 2D material (MOene) and its Janus structure are reported by first-principles calculations. The dynamic stability of these 2D materials are verified based on phonon spectra. The semiconductor properties of materials are based on the calculation of energy bands. The origin of piezoelectric polarization of MOene and its Janus structure is explained based on differential charge density and Bader charge analysis. The piezoelectric stress tensor of the material is calculated based on density functional perturbation theory (DFPT). The theoretical prediction results show that the piezoelectric properties of MOene and its Janus structure are better than those of 2D 2H-MoS2, and the in-plane piezoelectric coefficient d11 of Ti2OH2 reaches 6.09 pm/V. Our research shows that MOene and its Janus structure add an important member to the 2D piezoelectric material library, and provide a new sample for the study of piezoelectric properties based on the 2D material library.

A comprehensive computational investigation on the physical properties of the chalcogenide ternary Y2ZnX4 (Y = In, Ga; X = S, Se) compounds

In this study, the structural, elastic, vibrational, electronic, optical, thermodynamic, and thermoelectric properties of the chalcogenide ternary Y2ZnX4 (Y = In, Ga; X = S, Se) compounds are comprehensively investigated using the pseudopotential plane-wave (PP-PW) and full-potential linearized augmented plane wave (FP-LAPW) methods. The analysis of elastic and vibrational properties reveals the dynamic and mechanical stability of these compounds. The calculated energy band gaps, ranging from 1.47 eV (Ga2ZnSe4) to 2.55 eV (In2ZnS4) in the visible spectrum, decrease as X atoms are substituted with S to Se. All examined compounds demonstrate favorable optical absorption (α > 105 cm−1) in the ultraviolet region. Notably, Ga2ZnSe4 exhibits absorption red-shift towards the visible region at hν = 2.76 eV due to its lower energy band gap, making it a promising candidate for solar cells. The three-dimensional representation of Young's modulus indicates significant deviation from sphericity, revealing anisotropic behavior in all compounds. Pugh's ratio, Poisson's ratio, and Cauchy's pressure analysis suggest ductile behavior in all four chalcogenide ternary compounds. Additionally, all compounds, except In2ZnS4, display auxetic properties. Finally, the calculated thermoelectric properties identify Ga2ZnS4 and In2ZnS4 as promising candidates for high-performance thermoelectric applications, with high Seebeck coefficients of 1848 and 1936 μV/K, respectively, and ZT values approaching unit.

Interface coupling induced built-in electric fields accelerate electro-assisted uranium extraction over Co3O4@FeOx nanosheet arrays

Revealing the nature of enhanced electro-assisted uranium extraction activity by hetero-interface and M-O-H coordination bonds is an important and challenging task. Hence, Co3O4@FeOx nanosheet arrays with abundant M-O-H coordination bonds is fabricated as a binder-free and self-supporting electrocatalyst for electro-assisted uranium extraction from fluorine-containing uranium wastewater. As revealed by self-consistent energy band calculations and in-situ Kelvin Probe Force Microscopy (KPFM) analysis, the p-n heterojunction formed by Co3O4@FeOx provides a well-designed built-in electric field (BIEF), triggering the interfacial accumulation of uranium and accelerating the electro reduction kinetics of uranium. Consequently, Co3O4@FeOx shows remarkable U(VI) extraction ability (>95 %) in fluorine-containing uranium wastewater. By virtue of the XAFS spectra, free uranyl ions are captured by M-O-H on Co3O4@FeOx to form a sturdy 2 Oax-1 U-3 Oeq configuration, confirming the electrically driven separation of uranium and fluorine. Furthermore, DFT calculation indicates that the existent of M-O-H enhances the adsorption energy of uranium species, thus promoting uranium extraction efficiency.

Structural, Morphological, Spectroscopic, and Dielectric Properties of Ca-Mg Nanoferrites for High-frequency Applications

Introduction:: Ca-Mg nanoferrites of composition Ca0.5Mg0.5Fe2O4 were synthesized by wet chemical citrate precursor approach. Methods:: The prepared nanoparticles were characterized by an “X-ray diffractometer, Scanning electron microscopy, Diffused reflectance spectroscopy, and Impedance analyzer”. In the XRD pattern, the most intense reflection was observed from the (311) peak that corresponds to the cubic spinel phase of the prepared ferrite. Results:: The average size of all crystallites was calculated to be 19 nm. The sample's porosity was found to be 61%. In the SEM micrograph, uniformity in the size of the particles was detected with some agglomeration. The calculated energy band gap (1.91eV) reveals the semiconducting nature of the prepared material. Conclusion:: The high value of the real part of the dielectric constant (290) and the low value of loss tangent (0.17) reveals that the synthesized material can be useful in magnetic cores, microwave components, and other high-frequency applications.

(Invited) Epitaxial Growth Technique for Si1−X Sn x Binary Alloy Thin Films

Silicon tin (Si1−x Sn x ) binary alloys are attractive materials for next-generation Si-based photonics and thermoelectronics. The energy band calculations predicted that the conduction band at the Γ point is more rapidly decreased than the others by the Sn substitution, and direct band gap semiconductors can be realized at more than sufficient Sn content [1], although they varied from 25 to 90% by the calculation methods. The corresponding wavelength range will be matched to the optical communication band, suggesting Si1−x Sn x can be applied to near-infrared light source and detector. Another interest is the dramatic reduction of the thermal conductivity by the Sn substitution owing to the mass-difference phonon scattering. Theoretically [2], the thermal conductivity of bulk Si (145 Wm−1K−1 [3]) can be decreased to ~5 Wm−1K−1 by the 10% Sn substitution; the lowest thermal conductivity (3 Wm−1K−1) is obtained at 50% Sn, which is the lowest value among bulk group-IV alloys. The low thermal conductivity achieves high thermoelectric performance and can help to ensure temperature differences within small thermoelectric generators (TEGs) integrated on Si chips, as is the case of Si nanowire TEGs [4].In contrast to the theoretical studies mentioned above, experimental studies are very limited compared with other group-IV alloys such as silicon germanium and germanium tin. Difficulties of the Si1−x Sn x synthesizing are the extremely low solid solubility of Sn in Si (0.1%), a tenth of that in Ge, and the large (∼20%) mismatch between the Si and α-Sn lattices. Nevertheless, some research groups, including us, showed some possibilities to achieve a high Sn content Si1−x Sn x thin films (x>10%) experimentally; reported the optical properties such as photoluminescence and photo-absorption. However, the technology for freely controlling Sn content is still in its infancy; the Si1−x Sn x ’s thermoelectric properties have not been clarified yet. We will discuss the recent progress on the growth techniques of Si1−x Sn x thin films using solid phase epitaxy/crystallization [5-7], molecular beam epitaxy [8,9], sputtering [10], and the potential in thin-film TEGs application. Acknowledgments This work was partly supported by JSPS KAKENHI (Nos. 19K21971, 20H05188, and 21H01366), PRESTO (No. JPMJPR15R2), and CREST (No. JPMJCR19Q5) from JST, the TEPCO Memorial Foundation, and the Naito Research Grant.

Crystal growth, scintillation properties and silicon-germanium ratio concentration optimization of BGSO: An excellent scintillator for dual-readout calorimeter

Bismuth silicate-germanate (Bi4Ge3xSi3(1-x)O12) crystals are successfully grown with the modified Bridgman technique. The X-ray diffraction, transmittance spectra, radioluminescence spectra and scintillation properties of these crystals are investigated at different ratios of Ge and Si. Furthermore, the XEL peaks of BGSO crystals exhibit a red-shift with the increase of Ge content. Meanwhile, the light yield and energy resolution of crystals represent obviously variation with changing of Ge and Si contents in the crystal. Density-functional theory (DFT) calculations were performed for energy band structure and geometry optimizations of Bi4Ge2.4Si0.6O12 crystal. The calculated energy band of BGSO crystal is 3.957 eV, which is different from that of BSO and BGO crystals. The results of DOS and PDOS calculated by CASTEP package reveal that Si/Ge–O and Bi–O interactions play a critical role in the band gap of BGSO crystal.

In Situ Metal-Oxygen-Hydrogen Modified B-Tio2 @Co2 P-X S-Scheme Heterojunction Effectively Enhanced Charge Separation for Photo-assisted Uranium Reduction.

Photo-assisted uranium reduction from uranium mine wastewater is expected to overcome the competition between impurity ions and U(VI) in the traditional process. Here, B-TiO2 @Co2 P-X S-scheme heterojunction with metal-oxygen-hydrogen (M-O-H) is developed insitu modification for photo-assisted U(VI) (hexavalent uranium) reduction. Relying on the DFT calculation and Hard-Soft-Acid-Base (HSAB) theory, the introduction of metal-oxygen-hydrogen (M-O-H, hard base) metallic bonds in the B-TiO2 @Co2 P-X is found to enhance the hydrophilicity and the capture capability for uranyl ion (hard acid). Accordingly, B-TiO2 @Co2 P-500 hybrid nanosheets exhibit excellent U(VI) reduction ability (>98%) in the presence of competing ions. By self-consistent energy band calculations and in-situ KPFM spectral analysis, the formation of the internal electric field between B-TiO2 and Co2 P at the heterojunction is proven, offering a strong driving force and atomic transportation highway for accelerating the S-scheme charge carriers directed migration and promoting the photocatalytic reduction of uranium. This work provides a valuable route to explore the functionally modified photocatalyst with high-efficiency photoelectron separation for U(VI) reduction.

Spectroscopic properties (FT-IR, NMR and UV) and DFT studies of amodiaquine

Amodiaquine (AQ) was synthesized by a condensation reaction and characterized by experimental FT-IR, 1H and 13C nuclear magnetic resonance (NMR) and UV spectroscopies. In the present work, Density Functional Theory (DFT) calculations using B3LYP method with 6–311++G(d,p) and 6–311++G(2d, p) basis sets were performed, first, to confirm its structure, then to explain its reactive nature through its molecular properties such as natural charges, local and global reactivity descriptors or natural bond orbital (NBO). The 1H and 13C NMR chemical shifts were calculated by using the gauge-independent atomic orbital (GIAO) method, while the electronic UV–Vis spectrum is predicted using the time-dependent density functional theory (TD-DFT). Globally, the computerized results showed close similarity with the experimental values.The calculated energy band gap (ELUMO-EHOMO) value of AQ was found to be 4.09 eV suggesting that it could be considered as a hard molecule with high stability, supported by global reactivity descriptors. Molecular electrostatic potential (MEP) analysis revealed heteroatoms (oxygen and nitrogen) as the most putative nucleophilic sites when hydrogen atoms to which they are linked appear as electrophilic sites. The potential use of amodiaquine as non-linear optical (NLO) material and its thermodynamic indicators have also been assessed.

Investigation of optoelectronic properties of half-Heusler KZnN and KZnP compounds

This is to investigate the structural, mechanical, electronic and optical properties of half-Heusler KZnN and KZnP compounds. The ab initio method based on density functional theory is employed. The study of structural properties has allowed us to verify the cubic structure type I that is the most stable among the three possible atomic arrangements for the two half-Heusler compounds. The mechanical stability is checked, since the calculated elastic constants obey the stability criteria of cubic. Our calculations have demonstrated that KZnN is a ductile material that is considerably stiffer than KZnP, which exhibits brittleness. The obtained results for the electronic properties with mBJ-GGA approximation reveal a semiconductor behavior with a band gap along Γ as estimated at 0.3 eV and 0.9 eV for KZnN and KZnP compounds, respectively. In addition, the optical properties have been studied by analyzing the variation of different parameters such as dielectric function, refractive index, reflectivity, absorption coefficient and conductance as a function of photon’s energy for a wide range; 0 - 40 eV. The origin of peaks in the optical spectra is determined in terms of calculated energy band structures. This work has predicted strong absorption in the ultraviolet field.

Electron regulation and gas-sensitivity analysis of hBN-Graphene lateral heterojunctions——First principle study

In this paper, the first-principle calculations of the lateral heterojunction model synthesized by hBN-Graphene were carried out, and it was found that the bandgap of graphene varied with the change in the proportion of hBN, and the bandgap was best regulated with a bandgap of 1.177 eV when the proportion of hBN was 66.67 %. At this time, the adsorption structures of HCN, CO, NH3, and Cl2 were established and energy band calculations were performed on the hBN and Graphene portions of the hBN-Graphene lateral heterojunctions, respectively, and it was found that the adsorption of Cl2 resulted in a significant change in the band gap, which showed a very high electrical sensitivity. To further investigate the adsorption mechanism of Cl2 on the surface of hBN-Graphene lateral heterojunction, the energy band structure, PDOS, charge transfer, adsorption energy, and recovery time of each stabilized adsorption site of Cl2 on the surface of hBN-Graphene lateral heterojunction were calculated. The results show that the adsorption of Cl2 on the surface of hBN-Graphene lateral heterojunction is a stable chemisorption, and the band gap of C-Top1 increases to 1.274 eV, and the band gaps of C-Top3, N-Top1, and N-Top2 decrease to 0.684 eV, 0.376 eV, and 0.398 eV, respectively, and the changes of band gaps are significant and easy to be electrically detection. The recovery time of Cl2 on the surface of hBN-Graphene lateral heterojunction was 7.36 s–2.59 s in visible light and in the temperature interval of 273 K–283 K. The recovery time of Cl2 on the surface of hBN-Graphene lateral heterojunction was 7.36 s–2.59 s in visible light and in the temperature interval of 273 K–283 K. These findings have implications for the research and application of graphene-based Cl2 gas sensors.

Development of Flexible Semiconductors Based on g-C3N4/Cu2O P–N Heterojunction for Triboelectric Nanogenerator Application

This research aims to develop flexible semiconductors for triboelectric nanogenerator (TENG) applications. The sample powders of graphitic carbon nitride (g-C3N4) and copper (I) oxide (Cu2O) as N-type and P-type semiconductors, respectively, were synthesized. The semiconductors were prepared to be a composite film with alginate. The structure, morphology, and purity of the N- and P-type semiconductors were characterized using X-Ray diffraction and scanning electron microscopy techniques. Through the optical characterization, the N-type semiconductor showed the calculated energy band gap of 2.80 eV, while the P-type semiconductor was 1.90 eV. The P–N junction property of prepared samples was confirmed using a nonlinear current–voltage characteristic. After that, two flexible semiconductors were frictional paired for TENG. Through a vertical contact-separation mode, the P–N junction-based TENG produced a maximum output voltage and current of 3.90 V and 0.44 µA, respectively, with a maximum output power of 0.35 µW at 10 MΩ. In summary, the present work achieved the preparation of flexible P- and N-type semiconductors. The feasibility to harvest the mechanical energy was demonstrated in the TENG configuration. This idea is crucial for the future development of flexible harvesting/sensing devices using a novel concept.

Single step facile synthesis of Cu-SnO2/ZnO nanocomposite photocatalyst for methylene blue dye degradation in aqueous solution

A Cu-SnO2/ZnO nanocomposite was prepared using a single-step facile synthesis method, sol–gel, for photocatalyst application. The XRD of Cu-SnO2/ZnO nanocomposite shows SnO2 and ZnO have tetragonal rutile and hexagonal wurtzite, which is similar to HRTEM and SAED data. The crystallite sizes of SnO2, ZnO, Cu-SnO2, SnO2/ZnO, and Cu-SnO2/ZnO are 8.50 nm, 29.12 nm, 7.10 nm, 6.42 nm, and 3.50 nm, respectively. The calculated energy band gap of SnO2, ZnO, Cu-SnO2, and Cu-SnO2/ZnO from the DRS measurements is 3.60 eV, 3.20 eV, 3.34 eV, 3.48 eV, and 3.09 eV, respectively. The photoluminescence spectroscopy shows that Cu-SnO2/ZnO nanocomposite has a higher defect density than another sample. The Fourier Transform Infrared (FTIR) spectroscopy identifies the functional groups of the Cu-SnO2/ZnO powder samples. The EDS spectra of the synthesized Cu-SnO2/ZnO nanocomposite indicated the existence of the elements of Cu, Sn, Zn, and O, respectively. The photocatalyst activities of Cu-SnO2/ZnO have higher efficiency, ~78%, than other samples.

Electronic structure and optical absorption property of BaTiO3/BiCoO3

In this paper, we calculated the different forms of BaTiO3/BiCoO3 composite structure, predicting their visible light absorption performance based on the electronic structure using the first principles calculations. Firstly, six possible compounds that come from BaTiO3 and BiCoO3 were constructed. By calculating the different antiferromagnetic (AFM) structures of strip, columnar, and layered composite structures, it is found that the ground state of the composite structure changes to G‐type AFM structure from C‐type AFM structure of pure BiCoO3 under the influence of BaTiO3. Energy band calculations show that band gaps of three composite structures are smaller than those of pure BaTiO3 and pure BiCoO3. Furthermore, density of states analysis shows that the conduction band minimum (CBM) and valence band maximum (VBM) of three composite structures are mainly from the contribution of Co 3d and O 2p. For the characteristic that CBM and VBM of materials come from different atoms, it would reduce the recombination opportunities of electrons and holes and is conducive to the increase of photoelectric conversion efficiency under visible light irradiation. The calculation of optical properties shows that optical absorption coefficients of three composite structures are much larger than that of BaTiO3, especially the layered composite structure. There is a high absorption peak near 500 nm of the solar spectral irradiation maximum, which is significantly important to improve the optical energy conversion efficiency of the composite materials. The work provides an effective way for the application of wide band gap ferroelectric materials in ferroelectric photovoltaic.

First-Principles Calculation of Structural, Electronic, and Optical Properties of Cubic Perovskite CsPbF3

Lead halide perovskites have attracted considerable attention as one of the most promising materials for optoelectronic applications. The structural, electronic, and optical properties of the cubic perovskite CsPbF3 were studied using density functional theory in conjunction with plane waves, norm-conserving pseudopotentials, and Perdew-Berg-Erzenhof flavor of generalized gradient approximation. The obtained structural parameters are a good agreement with the experimentally measured and other’s theoretically predicted values. The obtained electronic band structure revealed that cubic CsPbF3 has a direct fundamental band gap of 2.99 eV at point R. The calculated energy band gaps at the high symmetry points agree with the other available theoretical results. The GW method is adapted to correct the underestimated fundamental energy gap value to 4.05 eV. The contribution of the different bands was analyzed from the total and partial density of states. The electron densities show that Cs and F have strong ionic bonds, whereas Pb and F have strong covalent bonds. The optical properties of CsPbF3 were calculated using the density functional perturbation theory and Kramers-Kronig relations. The wide and direct bandgap nature and the calculated optical properties imply that cubic CsPbF3 can be used in optical and optoelectronic devices for high frequencies visible and low frequencies ultraviolet electromagnetic radiation.