The optical properties of α-BeH2 in an Orthorhombic crystal structure with the space group (Ibam) are investigated. We have calculated the optical properties including dielelectric function, refractive index and exti...The optical properties of α-BeH2 in an Orthorhombic crystal structure with the space group (Ibam) are investigated. We have calculated the optical properties including dielelectric function, refractive index and extinction coefficient, using density functional approach. A theoretical explanation of the relationship between the dielectric function and other optical constants has been provided. Furthermore, the real and imaginary components of the dielectric function have been examined. The effects of the exchange-correlation potentials (GGA and GGA + U) applied on this compound’s absorption peaks and edges have also been investigated. It was found that using the GGA + U approximation caused the conduction band to shift, which in turn caused the initial absorption peak to shift.展开更多
本文基于密度泛函理论(DFT)的GGA+U方法,应用Materials Studio 5.0软件包中的CASTEP程序模拟计算了Al掺杂锐钛矿型TiO2和N-Al共掺杂锐钛矿型TiO2的电子结构。计算结果表明:Al掺杂和N-Al共掺杂均能够降低TiO2的带隙值。Al掺杂是由于Al的3...本文基于密度泛函理论(DFT)的GGA+U方法,应用Materials Studio 5.0软件包中的CASTEP程序模拟计算了Al掺杂锐钛矿型TiO2和N-Al共掺杂锐钛矿型TiO2的电子结构。计算结果表明:Al掺杂和N-Al共掺杂均能够降低TiO2的带隙值。Al掺杂是由于Al的3s和3p态使导带底端下移而导致TiO2的带隙变窄;而N-Al共掺杂由于在体系中引入了N2p态,使导带底端向能量更低的方向移动,比Al单独掺杂时具有更低的带隙值。该研究结果很好地解释了Al掺杂以及N-Al共掺杂诱使TiO2的导带底端下移,禁带宽度减小,导致光谱响应范围红移的内在原因。展开更多
The electronic structures and properties of PuO2 and Pu2O3 have been studied according to the first principles by using the all-electron projector-augmented-wave （PAW） method. The local density approximation （LDA）...The electronic structures and properties of PuO2 and Pu2O3 have been studied according to the first principles by using the all-electron projector-augmented-wave （PAW） method. The local density approximation （LDA）＋U and the generalized gradient approximation （GGA）＋U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Pu 5f electrons. We discuss how the properties of PuO2 and Pu2O3 are affected by choosing the values of U and exchange-correlation potential. Also, the oxidation reaction of Pu2O3, leading to the formation of PuO2, and its dependence on U and exchange-correlation potential have been studied. Our results show that by choosing an appropriate U it is possible to consistently describe structural, electronic, and thermodynamic properties of PuO2 and Pu2O3, which enable the modelling of the redox process involving Pu-based materials.展开更多
In this work, we perform DFT ＋ U periodic calculations to study geometrical and electronic structures and oxygen vacancy formation energies of SmxCayCe1-x-yO2-δ systems （x = 0.0312, 0.0625, 0.125 and 0.250; y = 0.0...In this work, we perform DFT ＋ U periodic calculations to study geometrical and electronic structures and oxygen vacancy formation energies of SmxCayCe1-x-yO2-δ systems （x = 0.0312, 0.0625, 0.125 and 0.250; y = 0.0312, 0.0625, 0.125 and 0.250; δ = 0.0312, 0.0625, 0.125, 0.250 and 0.50） with different oxygen vacancy and doping concentrations. The calculated results show that the VI-Sm3＋-V2 structures where there is a position relationship of the face diagonal between V1 and V2 both nearest to Sm3＋ have the lowest energy configurations. The study on electronic structures of the SmxCayCe1-x-yO2-δ systems finds that excess electrons arise from oxygen vacancies and are localized on f-level traps of their neighbor Ce, and Ca2＋ and Sm3＋ co-doping effectively restrains the reduction of Ce4＋. In order to avoid the existence of Ce3＋, x and y must be both larger than 0.0625 as δ = 0.125 or δ must be smaller than 0.125 as x = y = 0.0625. The Ce3＋/Ce4＋ change ratio k has an obvious monotonous increase with increasing the vacancy oxygen concentration. The introduction of Sm3＋ decreases k. In addition, the doped Sm3＋ can restrain the reduction of Ce4＋ when the V1-Sm3＋-V2 structure with a face diagonal position relationship in lower reduced atmosphere exists. It need be pointed out that the Sm025Ce07501.5 system should be thought of as a Sm-doped Ce2O3 one.展开更多
The influence of oxygen defects upon the electronic properties of Nb-doped TiO2 has been studied by using the general gradient approximation （GGA）＋U method. Four independent models （i.e., an undoped anatase cell, ...The influence of oxygen defects upon the electronic properties of Nb-doped TiO2 has been studied by using the general gradient approximation （GGA）＋U method. Four independent models （i.e., an undoped anatase cell, an anatase cell with a Nb dopant at Ti site （NbTi）, an anatase cell with a Nb-dopant and an oxygen vacancy （NbTi＋Vo）, and an anatase cell with a Nb-dopant and an interstitial oxygen （NbTi＋Oi）） were considered. The density of states, effective mass, Bader charge, charge density, and electron localization function were calcul^ited. The results show that in the NbTi＋Vo cell both eg and t2g levels of Ti 3d orbits make contributions to the electronic conductivity, and the oxygen vacancies （Vo） collaborate with Nb-dopants to favor the high electrical conductivity by inducing the Nb-dopants to release more excess charges. In NbTi＋Oi, an unoccupied impurity level appears in the band gap, which served as an acceptor level and suppressed the electronic conductivity. The results qualitatively coincide with experimental results and possibly provide insights into the preparation of TCOs with desirable conductivity.展开更多
The electronic structures and optical properties of β-Ga_2O_3 and Si-and Sn-doped β-Ga_2O_3 are studied using the GGA + U method based on density functional theory. The calculated bandgap and Ga 3d-state peak of β-...The electronic structures and optical properties of β-Ga_2O_3 and Si-and Sn-doped β-Ga_2O_3 are studied using the GGA + U method based on density functional theory. The calculated bandgap and Ga 3d-state peak of β-Ga_2O_3 are in good agreement with experimental results. Si-and Sn-doped β-Ga_2O_3 tend to form under O-poor conditions, and the formation energy of Si-doped β-Ga_2O_3 is larger than that of Sn-doped β-Ga_2O_3 because of the large bond length variation between Ga–O and Si–O. Si-and Sn-doped β-Ga_2O_3 have wider optical gaps than β-Ga_2O_3, due to the Burstein–Moss effect and the bandgap renormalization effect. Si-doped β-Ga_2O_3 shows better electron conductivity and a higher optical absorption edge than Sn-doped β-Ga_2O_3, so Si is more suitable as a dopant of n-type β-Ga_2O_3, which can be applied in deep-UV photoelectric devices.展开更多
The electronic band structures, densities of states （DOSs）, and projected densities of states （PDOSs） of the wurtzite In1-xGaxN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation （GG...The electronic band structures, densities of states （DOSs）, and projected densities of states （PDOSs） of the wurtzite In1-xGaxN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation （GGA） and GGA＋U in density functional theory. Our calculations suggest that in the case of wurtzite InN it is important to apply an on-site Hubbard correction to both the d states of indium and the p states of nitrogen in order to recover the correct energy level symmetry and obtain a reliable description of the InN band structure. The method is used to study the electronic properties of the wurtzite In1-xGaxN. The conduction band minimum （CBM） energy increases, while the valence band maximum （VBM） energy decreases with the increase of the gallium concentration. The effect leads to broadening the band gap （BG） and the valence band width （VBW）. Furthermore, the compressive strain in the crystal can cause the BG and the VBW to increase with the increase of gallium concentrations.展开更多
The optical properties of thermally annealed TiO_2 samples depend on their preparation process, and the TiO_2 thin films usually exist in the form of anatase or rutile or a mixture of the two phases. The electronic st...The optical properties of thermally annealed TiO_2 samples depend on their preparation process, and the TiO_2 thin films usually exist in the form of anatase or rutile or a mixture of the two phases. The electronic structures and optical properties of anatase and rutile TiO_2 are calculated by means of a first-principles generalized gradient approximation（GGA） ＋U approach. By introducing the Coulomb interactions on 3d orbitals of Ti atom（U^d） and 2p orbitals of O atom（U^p）, we can reproduce the experimental values of the band gap. The optical properties of anatase and rutile TiO_2 are obtained by means of the GGA＋U method, and the results are in good agreement with experiments and other theoretical data. Further, we present the comparison of the electronic structure, birefringence, and anisotropy between the two phases of TiO_2. Finally,the adaptability of the GGA＋U approach has been discussed.展开更多
The ab initio generalized gradient approximation (GGA)+U study of multiferroic (La Bi )<sub>2</sub>FeCrO<sub>6</sub> in pnma structure and ferri-magnetic order, including Hubbard corrections ( ...The ab initio generalized gradient approximation (GGA)+U study of multiferroic (La Bi )<sub>2</sub>FeCrO<sub>6</sub> in pnma structure and ferri-magnetic order, including Hubbard corrections ( eV) for transition metal/rare earth d-electrons with 20 atoms cell, shows optimum local magnetic moments of (Cr , Fe equal to (−2.56, 4.14) μB and an ideal spin-down band gap of 1.54 eV. Tuned-band gap La-substituted double oxide perovskites BFCO should exhibit enhanced visible-light absorption and carrier mobility, thus could be convenient light absorbers and then efficient alternatives to wide-gap chalcopyrite absorber-based solar cells failing to achieve highest power conversion efficiencies, and even compete with their metal-organic halide perovskites counterparts.展开更多
The phase diagram of HfO_2–TiO_2 system shows that when Ti content is less than 33.0 mol%, HfO_2–TiO_2 system is monoclinic; when Ti content increases from 33.0 mol% to 52.0 mol%, it is orthorhombic; when Ti content...The phase diagram of HfO_2–TiO_2 system shows that when Ti content is less than 33.0 mol%, HfO_2–TiO_2 system is monoclinic; when Ti content increases from 33.0 mol% to 52.0 mol%, it is orthorhombic; when Ti content reaches more than 52.0 mol%, it presents rutile phase. So, we choose the three phases of HfO_2–TiO_2 alloys with different Ti content values. The electronic structures and optical properties of monoclinic, orthorhombic and rutile phases of HfO_2–TiO_2 alloys are obtained by the first-principles generalized gradient approximation（GGA） ＋U approach, and the effects of Ti content and crystal structure on the electronic structures and optical properties of HfO_2–TiO_2 alloys are investigated. By introducing the Coulomb interactions of 5 d orbitals on Hf atom（U_1~d）, those of 3 d orbitals on Ti atom（U_2~d）, and those of 2 p orbitals on O atom（Up） simultaneously, we can improve the calculation values of the band gaps, where U_1~d, U_2~d, and Up values are 8.0 eV, 7.0 eV, and 6.0 eV for both the monoclinic phase and orthorhombic phase, and 8.0 eV, 7.0 eV, and 3.5 eV for the rutile phase. The electronic structures and optical properties of the HfO_2–TiO_2 alloys calculated by GGA ＋U_1~d（U_1~d= 8.0 eV） ＋U_2~d（U_2~d= 7.0 eV） ＋U^p（U^p= 6.0 eV or 3.5 eV） are compared with available experimental results.展开更多
The prospect ofα-Ga2O3 in optical and electrical devices application is fascinating.In order to obtain better performance,Ge and F elements with similar electronegativity and atomic size are selected as dopants.Based...The prospect ofα-Ga2O3 in optical and electrical devices application is fascinating.In order to obtain better performance,Ge and F elements with similar electronegativity and atomic size are selected as dopants.Based on density functional theory(DFT),we systematically research the electronic structure and optical properties of dopedα-Ga2O3 by GGA+U calculation method.The results show that Ge atoms and F atoms are effective n-type dopants.For Ge-dopedα-Ga2O3,it is probably obtained under O-poor conditions.However,for F-dopedα-Ga2O3,it is probably obtained under O-rich conditions.The doping system of F element is more stable due to the lower formation energy.In this investigation,it is found that two kinds of doping can reduce theα-Ga2O3 band gap and improve the conductivity.What is more,it is observed that the absorption edge after doping has a blue shift and causes certain absorption effect on the visible region.Through the whole scale of comparison,Ge doping is more suitable for the application of transmittance materials,yet F doping is more appropriate for the application of deep ultraviolet devices.We expect that our research can provide guidance and reference for preparation ofα-Ga2O3 thin films and photoelectric devices.展开更多
Using first-principles calculations in the generalized gradient approximation plus on-site Coulomb interaction(GGA+U) scheme, the effects of internal structural parameters x and U on the electronic structure of YbB6 a...Using first-principles calculations in the generalized gradient approximation plus on-site Coulomb interaction(GGA+U) scheme, the effects of internal structural parameters x and U on the electronic structure of YbB6 are investigated. The results show that the band gap of YbB6 increases with x increasing, and does not change with U. It not only illustrates the influence of internal structural parameter x on band gap, but also explains the discrepancy between the previous experimental result and the theoretical prediction. In addition, the electronic structure and density of states reveal that there exist the interactions between B atoms in different cages, and that a small band gap can form around the Fermi level(EF). The present work plays a leading role in ascertaining the relation between crystal structure and electronic property for the further analysis of its topological properties.展开更多
Computational calculations using density functional theory(DFT) were performed for the first time using the full potential linearized augmented plane wave plus local orbital method(FP-LAPW + LO) to determine the struc...Computational calculations using density functional theory(DFT) were performed for the first time using the full potential linearized augmented plane wave plus local orbital method(FP-LAPW + LO) to determine the structural, elastic, electronic and magnetic properties of europium-based cubic perovskites EuYO_(3)(Y=Cr, Mn, Fe). The exchange correlation potentials of GGA along with some analytical methods were adopted for the computation of structural and elastic properties. Moreover, the GGA + U formalism was also added for obtaining more precise electronic and magnetic properties, particularly to address the Eu-4f and Y-3d orientations in the spin-polarized double cell symmetry. The observed lattice parameters of these compounds are consistent with experiment. The observed bulk moduli predict that EuCrO_(3) is harder and less compressible than EuMnO_(3) and EuFeO_(3). The calculated tolerance factors of these compounds are within the cubic symmetry range. Our computed critical radius of EuCrO_(3) shows that EuCrO_(3) has a larger migration energy. Based on their elastic properties, these compounds are ductile in nature. We also computed the thermal properties of these compounds. The band structures and density of states show that these compounds are metallic in character. The lowest ground state energy and magnetic moments of these compounds expose their ferromagnetic nature. The metallic nature and strong ferromagnetism of these compounds make them promising applicants for application in spintronic.展开更多
文摘The optical properties of α-BeH2 in an Orthorhombic crystal structure with the space group (Ibam) are investigated. We have calculated the optical properties including dielelectric function, refractive index and extinction coefficient, using density functional approach. A theoretical explanation of the relationship between the dielectric function and other optical constants has been provided. Furthermore, the real and imaginary components of the dielectric function have been examined. The effects of the exchange-correlation potentials (GGA and GGA + U) applied on this compound’s absorption peaks and edges have also been investigated. It was found that using the GGA + U approximation caused the conduction band to shift, which in turn caused the initial absorption peak to shift.
文摘本文基于密度泛函理论(DFT)的GGA+U方法,应用Materials Studio 5.0软件包中的CASTEP程序模拟计算了Al掺杂锐钛矿型TiO2和N-Al共掺杂锐钛矿型TiO2的电子结构。计算结果表明:Al掺杂和N-Al共掺杂均能够降低TiO2的带隙值。Al掺杂是由于Al的3s和3p态使导带底端下移而导致TiO2的带隙变窄;而N-Al共掺杂由于在体系中引入了N2p态,使导带底端向能量更低的方向移动,比Al单独掺杂时具有更低的带隙值。该研究结果很好地解释了Al掺杂以及N-Al共掺杂诱使TiO2的导带底端下移,禁带宽度减小,导致光谱响应范围红移的内在原因。
基金Project supported by the National Natural Science Foundation of China (Grant No 10604010)
文摘The electronic structures and properties of PuO2 and Pu2O3 have been studied according to the first principles by using the all-electron projector-augmented-wave （PAW） method. The local density approximation （LDA）＋U and the generalized gradient approximation （GGA）＋U formalisms have been used to account for the strong on-site Coulomb repulsion among the localized Pu 5f electrons. We discuss how the properties of PuO2 and Pu2O3 are affected by choosing the values of U and exchange-correlation potential. Also, the oxidation reaction of Pu2O3, leading to the formation of PuO2, and its dependence on U and exchange-correlation potential have been studied. Our results show that by choosing an appropriate U it is possible to consistently describe structural, electronic, and thermodynamic properties of PuO2 and Pu2O3, which enable the modelling of the redox process involving Pu-based materials.
基金Supported by the National Natural Science Foundation of China(No.51474133)Inner Mongolia Natural Science Foundation(No.2016MS0513)
文摘In this work, we perform DFT ＋ U periodic calculations to study geometrical and electronic structures and oxygen vacancy formation energies of SmxCayCe1-x-yO2-δ systems （x = 0.0312, 0.0625, 0.125 and 0.250; y = 0.0312, 0.0625, 0.125 and 0.250; δ = 0.0312, 0.0625, 0.125, 0.250 and 0.50） with different oxygen vacancy and doping concentrations. The calculated results show that the VI-Sm3＋-V2 structures where there is a position relationship of the face diagonal between V1 and V2 both nearest to Sm3＋ have the lowest energy configurations. The study on electronic structures of the SmxCayCe1-x-yO2-δ systems finds that excess electrons arise from oxygen vacancies and are localized on f-level traps of their neighbor Ce, and Ca2＋ and Sm3＋ co-doping effectively restrains the reduction of Ce4＋. In order to avoid the existence of Ce3＋, x and y must be both larger than 0.0625 as δ = 0.125 or δ must be smaller than 0.125 as x = y = 0.0625. The Ce3＋/Ce4＋ change ratio k has an obvious monotonous increase with increasing the vacancy oxygen concentration. The introduction of Sm3＋ decreases k. In addition, the doped Sm3＋ can restrain the reduction of Ce4＋ when the V1-Sm3＋-V2 structure with a face diagonal position relationship in lower reduced atmosphere exists. It need be pointed out that the Sm025Ce07501.5 system should be thought of as a Sm-doped Ce2O3 one.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51002135 and 51172200)the Fundamental Research Funds for the Central Universities of Ministry of Education of China(Grant No.2013QNA4011)
文摘The influence of oxygen defects upon the electronic properties of Nb-doped TiO2 has been studied by using the general gradient approximation （GGA）＋U method. Four independent models （i.e., an undoped anatase cell, an anatase cell with a Nb dopant at Ti site （NbTi）, an anatase cell with a Nb-dopant and an oxygen vacancy （NbTi＋Vo）, and an anatase cell with a Nb-dopant and an interstitial oxygen （NbTi＋Oi）） were considered. The density of states, effective mass, Bader charge, charge density, and electron localization function were calcul^ited. The results show that in the NbTi＋Vo cell both eg and t2g levels of Ti 3d orbits make contributions to the electronic conductivity, and the oxygen vacancies （Vo） collaborate with Nb-dopants to favor the high electrical conductivity by inducing the Nb-dopants to release more excess charges. In NbTi＋Oi, an unoccupied impurity level appears in the band gap, which served as an acceptor level and suppressed the electronic conductivity. The results qualitatively coincide with experimental results and possibly provide insights into the preparation of TCOs with desirable conductivity.
基金Project supported by the Science and Technology Program of Guangdong Province,China(Grant No.2015B010112002)the Science and Technology Project of Guangzhou City,China(Grant No.201607010250)
文摘The electronic structures and optical properties of β-Ga_2O_3 and Si-and Sn-doped β-Ga_2O_3 are studied using the GGA + U method based on density functional theory. The calculated bandgap and Ga 3d-state peak of β-Ga_2O_3 are in good agreement with experimental results. Si-and Sn-doped β-Ga_2O_3 tend to form under O-poor conditions, and the formation energy of Si-doped β-Ga_2O_3 is larger than that of Sn-doped β-Ga_2O_3 because of the large bond length variation between Ga–O and Si–O. Si-and Sn-doped β-Ga_2O_3 have wider optical gaps than β-Ga_2O_3, due to the Burstein–Moss effect and the bandgap renormalization effect. Si-doped β-Ga_2O_3 shows better electron conductivity and a higher optical absorption edge than Sn-doped β-Ga_2O_3, so Si is more suitable as a dopant of n-type β-Ga_2O_3, which can be applied in deep-UV photoelectric devices.
基金Project supported by the National Natural Science Foundation of China(Grant No.50971094)the Natural Science Foundation of Beijing,China(Grant Nos.KZ201310028032 and 1092007)the Domestic Visiting Program for the Graduate Students of Inner Mongolia University,China
文摘The electronic band structures, densities of states （DOSs）, and projected densities of states （PDOSs） of the wurtzite In1-xGaxN with x=0, 0.0625, 0.125 are studied using the generalized-gradient approximation （GGA） and GGA＋U in density functional theory. Our calculations suggest that in the case of wurtzite InN it is important to apply an on-site Hubbard correction to both the d states of indium and the p states of nitrogen in order to recover the correct energy level symmetry and obtain a reliable description of the InN band structure. The method is used to study the electronic properties of the wurtzite In1-xGaxN. The conduction band minimum （CBM） energy increases, while the valence band maximum （VBM） energy decreases with the increase of the gallium concentration. The effect leads to broadening the band gap （BG） and the valence band width （VBW）. Furthermore, the compressive strain in the crystal can cause the BG and the VBW to increase with the increase of gallium concentrations.
基金supported by the National Natural Science Foundation of China(Grant Nos.11672087,11272107,and 11402252)
文摘The optical properties of thermally annealed TiO_2 samples depend on their preparation process, and the TiO_2 thin films usually exist in the form of anatase or rutile or a mixture of the two phases. The electronic structures and optical properties of anatase and rutile TiO_2 are calculated by means of a first-principles generalized gradient approximation（GGA） ＋U approach. By introducing the Coulomb interactions on 3d orbitals of Ti atom（U^d） and 2p orbitals of O atom（U^p）, we can reproduce the experimental values of the band gap. The optical properties of anatase and rutile TiO_2 are obtained by means of the GGA＋U method, and the results are in good agreement with experiments and other theoretical data. Further, we present the comparison of the electronic structure, birefringence, and anisotropy between the two phases of TiO_2. Finally,the adaptability of the GGA＋U approach has been discussed.
文摘The ab initio generalized gradient approximation (GGA)+U study of multiferroic (La Bi )<sub>2</sub>FeCrO<sub>6</sub> in pnma structure and ferri-magnetic order, including Hubbard corrections ( eV) for transition metal/rare earth d-electrons with 20 atoms cell, shows optimum local magnetic moments of (Cr , Fe equal to (−2.56, 4.14) μB and an ideal spin-down band gap of 1.54 eV. Tuned-band gap La-substituted double oxide perovskites BFCO should exhibit enhanced visible-light absorption and carrier mobility, thus could be convenient light absorbers and then efficient alternatives to wide-gap chalcopyrite absorber-based solar cells failing to achieve highest power conversion efficiencies, and even compete with their metal-organic halide perovskites counterparts.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11672087,11502058,and 11402252)
文摘The phase diagram of HfO_2–TiO_2 system shows that when Ti content is less than 33.0 mol%, HfO_2–TiO_2 system is monoclinic; when Ti content increases from 33.0 mol% to 52.0 mol%, it is orthorhombic; when Ti content reaches more than 52.0 mol%, it presents rutile phase. So, we choose the three phases of HfO_2–TiO_2 alloys with different Ti content values. The electronic structures and optical properties of monoclinic, orthorhombic and rutile phases of HfO_2–TiO_2 alloys are obtained by the first-principles generalized gradient approximation（GGA） ＋U approach, and the effects of Ti content and crystal structure on the electronic structures and optical properties of HfO_2–TiO_2 alloys are investigated. By introducing the Coulomb interactions of 5 d orbitals on Hf atom（U_1~d）, those of 3 d orbitals on Ti atom（U_2~d）, and those of 2 p orbitals on O atom（Up） simultaneously, we can improve the calculation values of the band gaps, where U_1~d, U_2~d, and Up values are 8.0 eV, 7.0 eV, and 6.0 eV for both the monoclinic phase and orthorhombic phase, and 8.0 eV, 7.0 eV, and 3.5 eV for the rutile phase. The electronic structures and optical properties of the HfO_2–TiO_2 alloys calculated by GGA ＋U_1~d（U_1~d= 8.0 eV） ＋U_2~d（U_2~d= 7.0 eV） ＋U^p（U^p= 6.0 eV or 3.5 eV） are compared with available experimental results.
基金Project supported by the National Natural Science Foundation of China(Grant No.51302215)the Natural Science Basic Research Program of Shaanxi Province,China(Grant Nos.2018JQ6084 and 2019JQ-860).
文摘The prospect ofα-Ga2O3 in optical and electrical devices application is fascinating.In order to obtain better performance,Ge and F elements with similar electronegativity and atomic size are selected as dopants.Based on density functional theory(DFT),we systematically research the electronic structure and optical properties of dopedα-Ga2O3 by GGA+U calculation method.The results show that Ge atoms and F atoms are effective n-type dopants.For Ge-dopedα-Ga2O3,it is probably obtained under O-poor conditions.However,for F-dopedα-Ga2O3,it is probably obtained under O-rich conditions.The doping system of F element is more stable due to the lower formation energy.In this investigation,it is found that two kinds of doping can reduce theα-Ga2O3 band gap and improve the conductivity.What is more,it is observed that the absorption edge after doping has a blue shift and causes certain absorption effect on the visible region.Through the whole scale of comparison,Ge doping is more suitable for the application of transmittance materials,yet F doping is more appropriate for the application of deep ultraviolet devices.We expect that our research can provide guidance and reference for preparation ofα-Ga2O3 thin films and photoelectric devices.
基金Project supported by the Special Project of Department of Education of Shannxi Province,China(Grant No.18JK0710)the Natural Science Foundation of Shannxi Province,China(Grant No.2019JQ-105)
文摘Using first-principles calculations in the generalized gradient approximation plus on-site Coulomb interaction(GGA+U) scheme, the effects of internal structural parameters x and U on the electronic structure of YbB6 are investigated. The results show that the band gap of YbB6 increases with x increasing, and does not change with U. It not only illustrates the influence of internal structural parameter x on band gap, but also explains the discrepancy between the previous experimental result and the theoretical prediction. In addition, the electronic structure and density of states reveal that there exist the interactions between B atoms in different cages, and that a small band gap can form around the Fermi level(EF). The present work plays a leading role in ascertaining the relation between crystal structure and electronic property for the further analysis of its topological properties.
基金Project supported by the Higher Education of Pakistan Under National Research Grant Program(NRPU)(Grant No:14408/NRPU/R&D/HEC/20212021)。
文摘Computational calculations using density functional theory(DFT) were performed for the first time using the full potential linearized augmented plane wave plus local orbital method(FP-LAPW + LO) to determine the structural, elastic, electronic and magnetic properties of europium-based cubic perovskites EuYO_(3)(Y=Cr, Mn, Fe). The exchange correlation potentials of GGA along with some analytical methods were adopted for the computation of structural and elastic properties. Moreover, the GGA + U formalism was also added for obtaining more precise electronic and magnetic properties, particularly to address the Eu-4f and Y-3d orientations in the spin-polarized double cell symmetry. The observed lattice parameters of these compounds are consistent with experiment. The observed bulk moduli predict that EuCrO_(3) is harder and less compressible than EuMnO_(3) and EuFeO_(3). The calculated tolerance factors of these compounds are within the cubic symmetry range. Our computed critical radius of EuCrO_(3) shows that EuCrO_(3) has a larger migration energy. Based on their elastic properties, these compounds are ductile in nature. We also computed the thermal properties of these compounds. The band structures and density of states show that these compounds are metallic in character. The lowest ground state energy and magnetic moments of these compounds expose their ferromagnetic nature. The metallic nature and strong ferromagnetism of these compounds make them promising applicants for application in spintronic.
