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AIP Conference Proceedings [Author(s) GREEN DESIGN AND MANUFACTURE: ADVANCED AND EMERGING APPLICATIONS: Proceedings of the 4th International Conference on Green Design and Manufacture 2018 - Ho Chi Minh, Vietnam (29–30 April 2018)] - Study of geometrical and electronic structure of lanthanum doped PbTiO3 and PbZrTiO3: First principles calculation
摘要： Structural and electronic properties of tetragonal (space group P4mm) of PbLaTiO3 and PLaZT are investigated using pseudopotential plane wave method within the local density approximation (LDA) and generalized gradient approximation (GGA) with virtual crystal approximation (VCA) calculation. The calculated structural parameters for PbLaTiO3 and PLZT are consistent with the obtainable experimental data (XRD) and previous calculations. The band structures show that PbLaTiO3 and PLaZT have small band gap about 1.600 eV and 2.263 eV compared with pure PbTiO3 and PZT respectively. The density of states show that the effect of B-site cation (Ti 3d and Zr 4d) was the important part of covalency for O 2p and La 5p in PbLaTiO3 and PLaZT. Our calculated results can be seen as a prediction for future investigations.
关键词： structural properties,lanthanum doped PbTiO3,electronic properties,PbZrTiO3,first principles calculation
更新于2025-09-04 15:30:14
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Electronic structures and optical properties of Fe/Co–doped cubic BaTiO3 ceramics
摘要： The electronic structures and the optical properties of Fe/Co–doped cubic BaTiO3 ceramics in which the Ti sites replaced partly and uniformly by Fe or Co chemical elements have been investigated using first–principles method based on the density functional theoretical framework. The calculated energy band structures indicate that Fe/Co–doped cubic BaTiO3 system has electrically conductivity while the purely BaTiO3 features the characteristic of semi–conductivity. In consistent with the energy band structures, some new peaks correlated to the impurity bands have arisen in the total density of state of the Fe/Co–doped BaTiO3 system due to the 3d orbital of Fe/Co atoms making an evidently contribution and a strong orbital hybridization incurred by d–d interaction and p–d interaction near the Fermi energy level being introduced by Fe/Co–doping. The analysis of optical properties, including the calculation of dielectric function, reflection spectrum and absorption spectrum of Fe/Co–doped BaTiO3 system, implied that their photoelectric properties can be improved by Fe/Co–doping due to the required activation energy for the photoelectron transition being reduced effectively. These phenomena such as red–shift phenomenon, the bridge effect of impurity bands and the strong orbital hybridization suggested that they can be as a potentially candidate for optoelectronic materials applied in the field of energy conversion.
关键词： Cubic BaTiO3,Fe/Co–doping,Optical properties,First–principles calculations
更新于2025-09-04 15:30:14
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Simultaneous Prediction of Atomic Structure and Stability of Nanoclusters in a Wide Area of Compositions
摘要： We present a universal method for the large-scale prediction of the atomic structure of clusters. Our algorithm performs the joint evolutionary search for all clusters in a given area of the compositional space and takes advantage of structural similarities frequently observed in clusters of close compositions. The resulting speedup is up to 50 times compared to current methods. This enables the first-principles studies of multi-component clusters with full coverage of a wide range of compositions. As an example, we report an unprecedented first-principles global optimization of 315 SinOm clusters with n ≤ 15 and m ≤ 20. The obtained map of Si-O cluster stability shows the existence of both expected (SiO2)n and unexpected (e.g. Si4O18) stable (magic) clusters, which can be important for miscellaneous applications.
关键词： atomic structure,nanoclusters,evolutionary algorithm,first-principles,stability
更新于2025-09-04 15:30:14
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Electron and phonon transport properties of layered Bi <sub/>2</sub> O <sub/>2</sub> Se and Bi <sub/>2</sub> O <sub/>2</sub> Te from first-principles calculations
摘要： Recent experiments indicated that both layered Bi2O2Se and Bi2O2Te are promising thermoelectric materials with low thermal conductivities. However, theoretical study on the thermoelectric properties, especially the phonon transport properties, is rare. In order to understand the thermoelectric transport mechanism, we here investigate the electron and phonon transport properties by using the first-principles calculations combined with the Boltzmann transport theory. Our results indicate that both Bi2O2Se and Bi2O2Te are semiconductors with indirect energy gaps of 0.87 eV and 0.21 eV within spin–orbit coupling, respectively. Large Seebeck coefficient and power factor are found in the p-type than the n-type for both compounds. Low lattice thermal conductivities at room temperature are obtained, 1.14 W m?1 K?1 for Bi2O2Se and 0.58 W m?1 K?1 for Bi2O2Te, which are close to the experimental values. It is found that the low-frequency optical phonon branches with higher group velocity and longer lifetime also make a main contribution to the lattice thermal conductivity. Interestingly, the lattice thermal conductivity exhibits obvious anisotropy especially for Bi2O2Te. These results are helpful for the understanding and optimization of thermoelectric performance of layered Bi2O2Se and Bi2O2Te.
关键词： thermoelectric,Bi2O2Se,lattice thermal conductivity,Bi2O2Te,first-principles
更新于2025-09-04 15:30:14
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First-Principles Insights into the Oxidation States and Electronic Structures of Ceria-Based Binary, Ternary and Quaternary Oxides
摘要： Ceria and ceria-based materials have versatile technological and industrial applications, physically ascribed to the flexible fluctuation of Ce oxidation state between Ce4+ and Ce3+. A considerable multi-disciplinary research has been spent to obtain Ce oxidation state, the crucial quantity regarding the application; however, a rigorous and physically correct determination of oxidation state is still lacking. Here we conduct first-principles DFT + U calculations to unambiguously determine the physical oxidation state of Ce in ceria-based materials such as the homogenous CenO2n-2 (n = 7, 9, 10, 11, 12), ceria doped by multivalent Ti and V, Ce-Ti(V)-O ternary compounds, and Ce-Ti-V-O quaternary compounds. The results show that Ce oxidation state depends on the local structure and chemical surrounding: Oxygen vacancy facilitates the transition from Ce4+ to Ce3+, consistent with the localization of Ce 4f electrons; Ti and V with the 3d energy levels higher than 4f energy levels of Ce generally tend to reduce Ce4+ to Ce3+ particularly under the oxygen-deficiency condition. The atom-resolved determination of Ce oxidation states in the complicated compounds offers great promise for understanding the physical and chemical behavior of ceria-based materials, and for rational design of novel ceria-based materials for application potentials.
关键词： Ceria-based materials,First-principles calculations,Electronic structures,DFT + U,Oxidation states
更新于2025-09-04 15:30:14
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Ultrafast defect dynamics: A new approach to all optical broadband switching employing amorphous selenium thin films
摘要： Optical switches offer higher switching speeds than electronics, however, in most cases utilizing the interband transitions of the active medium for switching. As a result, the signal suffers heavy losses. In this article, we demonstrate a simple and yet efficient ultrafast broadband all-optical switching on ps timescale in the sub-bandgap region of the a-Se thin film, where the intrinsic absorption is very weak. The optical switching is attributed to short-lived transient defects that form localized states in the bandgap and possess a large electron-phonon coupling. We model these processes through first principles simulation that are in agreement with the experiments.
关键词： electron-phonon coupling,optical switches,interband transitions,all optical broadband switching,first principles simulation,amorphous selenium thin films,ultrafast defect dynamics,sub-bandgap region,transient defects
更新于2025-09-04 15:30:14
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Mechanical, Electronic and Optical Properties of Two Phases of NbB4: First-Principles Calculations
摘要： As transition metal borides have been successfully synthesised, the study of the combination of transition metal and boron is another effective way to investigate the properties of boride. We have predicted the novel phase Amm2-NbB4. Using the Cambridge Serial Total Energy Package (CASTEP) code, we further researched on the mechanical, electronic and optical properties of C2/c- and Amm2-NbB4. It is found that both the phases of NbB4 are dynamically and mechanically stable at 0 and 100 GPa. Their Vickers hardness values are both 34 GPa, which indicate that they are hard materials. The band gap of C2/c-NbB4 is 0.145 eV, which indicates that it is a semiconductor (or metalloid) at 0 GPa. For the Amm2-NbB4, the band structure without band gap indicates it is a metal at 0 GPa. The optical properties of these two structures are similar. At 0 eV, the real part of dielectric function is 28.8 for C2/c-NbB4, and the real part value for Amm2-NbB4 is 43. We hope our work will provide some help to the experimental work about the technology of the material.
关键词： Mechanical Properties,Optical Properties,First-Principles Calculations,Electronic Properties,NbB4
更新于2025-09-04 15:30:14
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A First-Principles Study on the Adsorption of Small Molecules on Arsenene: Comparison of Oxidation Kinetics in Arsenene, Antimonene, Phosphorene and InSe
摘要： Arsenene, a new group V two-dimensional (2D) semiconducting material beyond phosphorene and antimonene, has recently gained an increasing attention owning to its various interesting properties which can be altered or intentionally functionalized by chemical reactions with various molecules. This work provides a systematic study on the interactions of arsenene with the small molecules, including H2, NH3, O2, H2O, NO, and NO2. It is predicted that O2, H2O, NO, and NO2 are strong acceptors, while NH3 serves as a donor. Importantly, it is shown a negligible charge transfer between H2 and arsenene which is ten times lower than that between H2 and phosphorene and about thousand times lower than that between H2 and InSe and antimonene. The calculated energy barrier for O2 splitting on arsenene is found to be as low as 0.67 eV. Thus, pristine arsenene may easily oxidize in ambient conditions as other group V 2D materials. On the other hand, the acceptor role of H2O on arsenene, similarly to the cases of antimonene and InSe, may help to prevent the proton transfer between H2O and O– species by forming acids, which suppresses further structural degradation of arsenene. The structural decomposition of the 2D layers upon interaction with the environment may be avoided due to the acceptor role of H2O molecules as the study predicts from the comparison of common group V 2D materials. However, the protection for arsenene is still required due to its strong interaction with other small environmental molecules. The present work renders the possible ways to protect arsenene from structure degradation and to modulate its electronic properties, which is useful for the material synthesis, storage and applications.
关键词： group V two-dimensional materials,electronic structure,first-principles calculations,O2 molecule splitting,arsenene
更新于2025-09-04 15:30:14
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Simulated annealing and first-principles study of substitutional Ga-doped graphene
摘要： The combination of Monte Carlo-based simulated annealing and ab initio calculations were applied to investigate the electronic and optical properties of substitutional Ga-doped graphene. During simulated annealing, it was observed the formation of gallium clusters, which may be an indication of the low dopant solubility. The obtained results indicate that the introduction of a single gallium atom in the graphene layer induces the formation of a band gap. Nevertheless, increasing the dopant concentration, the gap width fluctuates according to the number, odd or even, of dopant atoms. For an odd number, the gap width decreases with increasing dopant concentration. It was obtained that the structure distortions, produced by the introduction of the dopant atoms, induces significant changes in the electronic properties of the layer. Additionally, it is possible to infer that the optical absorption in the infrared region can be tuned as a function of the dopant concentration.
关键词： Simulated annealing,Ga-doped graphene,First-principles calculations,Optical properties,Electronic properties
更新于2025-09-04 15:30:14
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Vacancies inducing electronic and optical properties in 2D ZnO:Be/Mg
摘要： The structural, electronic and optical properties of the 2D ZnO:Mg/Be with oxygen or zinc vacancies were studied by First-principles calculation. Results show that the formation of vacancy defect in DL system is easier than in SL system. The band gap become narrow with introducing oxygen and zinc vacancy defects. It was also found that oxygen vacancies can induce an impurity level near VBM to improve the conductivity of system and Zn vacancies can not. Optical absorption spectra show that oxygen vacancy defect will cause blue-shift and Zn vacancy defect will cause red-shift. So, two kinds of vacancies give birth to the opposite optical properties. Therefore, vacancy defects in 2D ZnO:Mg/Be are very important defect to better the conductivity and potential application in photoelectron and photocatalysis.
关键词： First-principles calculation,Electronic structure,Optical properties,2D ZnO:Mg/Be
更新于2025-09-04 15:30:14