The first-principles calculations are performed to investigate the structural, mechanical property, hardness, and electronic structure of WCoB with 0, 8.33, 16.67, 25, and 33.33 at.% Mn doping content and W_2 CoB_2 wi...The first-principles calculations are performed to investigate the structural, mechanical property, hardness, and electronic structure of WCoB with 0, 8.33, 16.67, 25, and 33.33 at.% Mn doping content and W_2 CoB_2 with 0, 10, and 20 at.%Mn doping content. The cohesive energy and formation energy indicate that all the structures can retain good structural stability. According to the calculated elastic constants, Mn is responsible for the increase of ductility and Poisson＇s ratio and the decrease of Young＇s modulus, shear modulus, and bulk modulus. By using the population analysis and mechanical properties, the hardness is characterized through using the five hardness models and is found to decrease with the Mn doping content increasing. The calculated electronic structure indicates that the formation of a B–Mn covalent bond and a W–Mn metallic bond contribute to the decreasing of the mechanical properties.展开更多
Aiming at developing p-type semiconductors and modulating the band gap for photoelectronic devices and band engineering, we present the ab initio numerical simulation of the effect of codoping ZnO with Al, N and Mg on...Aiming at developing p-type semiconductors and modulating the band gap for photoelectronic devices and band engineering, we present the ab initio numerical simulation of the effect of codoping ZnO with Al, N and Mg on the crystal lattice and electronic structure. The simulations are based on the Perdew-Burke-Ernzerhof generalised-gradient approximation in density functional theory. Results indicate that electrons close to the Fermi level transfer effectively when Al, Mg, and N replace Zn and O atoms, and the theoretical results were consistent with the experiments. The addition of Mg leads to the variation of crystal lattice, expanse of energy band, and change of band gap. These unusual properties are explained in terms of the computed electronic structure, and the results show promise for the development of next-generation photoconducting devices in optoelectronic information science and technology.展开更多
Using first-principles calculations within the generalized gradient approximation （GGA） ＋U framework, we inves- tigate the effect of C doping on the structural and electronic properties of LiFePO4. The calculated f...Using first-principles calculations within the generalized gradient approximation （GGA） ＋U framework, we inves- tigate the effect of C doping on the structural and electronic properties of LiFePO4. The calculated formation energies indicate that C doped at O sites is energetically favoured, and that C dopants prefer to occupy 03 sites. The band gap of the C doped material is much narrow than that of the undoped one, indicating better electro- conductive properties. To maintain charge balance, the valence of the Fe nearest to C appears as Fe3＋, and it will be helpful to the hopping of electrons.展开更多
The electronic structure and optical properties of pure, C-doped, C~ codoped and C-F-Be cluster- doped ZnO with a wurtzite structure were calculated by using the density functional theory with the plane-wave ultrasoft...The electronic structure and optical properties of pure, C-doped, C~ codoped and C-F-Be cluster- doped ZnO with a wurtzite structure were calculated by using the density functional theory with the plane-wave ultrasoft pseudopotentials method. The results indicate that p-type ZnO can be obtained by C incorporation, and the energy level of Co above the valence band maximum is 0.36 eV. The ionization energy of the complex Zn16O14CF and ZnlsBeO14CF can be reduced to 0.23 and 0.21 eV, individually. These results suggest that the defect complex of ZnlsBeO14CF is a better candidate for p-type ZnO. To make the optical properties clear, we investigated the imaginary part of the complex dielectric function ofundoped and C-F-Be doped ZnO. We found that there is strong absorption in the energy region lower than 2.7 eV for the C-F-Be doped system compared to pure ZnO.展开更多
Impurity formation energy, electronic structure, and photocatalytic properties of C-, N-, or S-doped BiOCl are investigated by density-functional theory plus U calculations(DFT + U). Results show that the doping effec...Impurity formation energy, electronic structure, and photocatalytic properties of C-, N-, or S-doped BiOCl are investigated by density-functional theory plus U calculations(DFT + U). Results show that the doping effect of S is better than that of C or N on the tunable photocatalytic activities of BiOCl. At low concentration, S-doped BiOCl systems are the most stable under Bi-rich growth conditions because of their lower impurity-formation energy. Compared with the electronic structures of S-doped BiOCl, C-or N-doped BiOCl have relatively deeper impurity energy levels appearing in their band gap(except Bi_(36)O_(35)NCl_(36)), which may act as photogenerated carrier-recombination centers and reduce photocatalytic activity. At high concentration, S is substituted on the O lattice site system, whereas some S 3p states mix with the valence band; this mixture leads to an obvious band-gap decrease and continuum-state formation above the valence-band edge of BiOCl. Such activity is advantageous to photochemical catalysis response. Compared with pure Bi OCl and a low-concentration S-doped system, a high-concentration S-doped system shows an obvious redshift on the absorption edge and has better photocatalytic O_2 evolution performance.展开更多
Using the first-principles approach based upon the density functional theory （DFT）, we have studied the electronic structure of wurtzite ZnO systems doped with C at different sites. When Zn is substituted by C, the ...Using the first-principles approach based upon the density functional theory （DFT）, we have studied the electronic structure of wurtzite ZnO systems doped with C at different sites. When Zn is substituted by C, the system turns from a direct band gap semiconductor into an indirect band gap semiconductor, and donor levels are formed. When O is substituted by C, acceptor levels are formed near the top of the valence band, and thus a p-type transformation of the system is achieved. When the two kinds of substitution coexist, the acceptor levels are compensated for all cases, which is unfavorable for the p-type transformation of the system.展开更多
We perform a first-principles simulation to study the electronic and optical properties of wurtzite Zn1-xCuxO. The simulations are based upon the Perdew-Burke-Ernzerhof form of generalised gradient approximation withi...We perform a first-principles simulation to study the electronic and optical properties of wurtzite Zn1-xCuxO. The simulations are based upon the Perdew-Burke-Ernzerhof form of generalised gradient approximation within the density functional theory. Calculations are carried out in different concentrations. With increasing Cu concentration, the band gap of Znl-xCuxO decreases due to the shift of valence band. The imaginary part of the dielectric function indicates that the optical transition between O2p states in the highest valence band and Zn 4s states in the lowest conduction band shifts to the low energy range as the Cu concentration increases. Besides, it is shown that the insertion of Cu atom leads to redshift of the optical absorption edge. Meanwhile, the optical constants of pure ZnO and Zn0.75Cu0.250, such as loss function, refractive index and reflectivity, are discussed.展开更多
The structures and electronic properties of ZnO nanowires（NWs） of different diameters are investigated by employing the first-principles density functional theory. The results indicate that the oxygen vacancy（VO） ...The structures and electronic properties of ZnO nanowires（NWs） of different diameters are investigated by employing the first-principles density functional theory. The results indicate that the oxygen vacancy（VO） exerts a more evident influence on the band gap of the ZnO NWs. However, the effect will be weakened with the increase of the diameter. In addition, the energy band shifts downward due to the existence of VOand the offset decreases with the reduction of the VOconcentration. As the concentration of surface Zn atoms decreases, the conduction band shifts downward, while 2p electrons are lost in the oxygen vacancy, resulting in the split of valence band and the formation of an impurity level. Our findings agree well with the previous observations and will be of great importance for theoretical research based on ZnO NWs.展开更多
Based on the experimental study of the optical properties of K2Ti6O13 doped with Fe or Ag,their electronic structures and optical properties are studied by the first-principles method based on the density functional t...Based on the experimental study of the optical properties of K2Ti6O13 doped with Fe or Ag,their electronic structures and optical properties are studied by the first-principles method based on the density functional theory（DFT）. The calculated optical properties are consistent with the experiment results. K2Ti6O13 doped with substitutional Fe or Ag has isolated impurity bands mainly stemming from the hybridization by the Fe 3d states or Ag 4d states with Ti 3d states and O 2p states and the band gap becomes narrower, the absorption edge of K2Ti6O13 thus has a clear red shift and the absorption of visible light can be realized after doping. For Fe-doped K2Ti6O13, the impurity bands are in the middle of the band gap, suggesting that they can be used as a bridge for valence band electrons transition to the conduction band. For Ag-doped K2Ti6O13,the impurity bands form a shallow acceptor above the valence band and can reduce the recombination rate of photoexcited carriers.The experimental and calculated results are significant for the development of K2Ti6O13materials that have absorption under visible light.展开更多
Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functio...Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functional theory based on the full-potential linear augmented plane wave （FP-LAPW） method as implemented in the Wien2k code. In this approach the generalized gradient approximation （GGA） was used for the exchange-correlation （XC） potential. Our results showed that the substitution of RE ions in ZnO induced spins polarized localized states in the band gap. Moreover, the studied DMSs compounds retained half metallicity at dopant concentration x=0.625%for most of the studied elements, with 100%spin polarization at the Fermi level （EF）. The total magnetic moments of these compounds existed due to RE 4f states present at EF, while small induced magnetic moments existed on other non-magnetic atoms as well. Finally, the energy difference between far and near configurations was investigated. It was found that the room temperature ferromagnetism was possible for RE-doped ZnO at near configuration. Since the RE-RE separation was long enough （far configuration） for magnetic coupling, the system became paramagnetic or antiferromagnetic ground state.展开更多
We used density functional theory(DFT)calculations to study the influence of alkali earth metal element(AE)doping on the crystal structure and electronic band structure ofα-Si3N4.The diversity of atomic radii of alka...We used density functional theory(DFT)calculations to study the influence of alkali earth metal element(AE)doping on the crystal structure and electronic band structure ofα-Si3N4.The diversity of atomic radii of alkaline earth metal elements results in structural expansion when they were doped into theα-Si3N4 lattice.Formation energies of the doped structures indicate that dopants prefer to occupy the interstitial site under the nitrogen-deficient environment,while substitute Si under the nitrogen-rich environment,which provides a guide to synthesizingα-Si3N4 with different doping types by controlling nitrogen conditions.For electronic structures,energy levels of the dopants appear in the bottom of the conduction band or the top of the valence band or the forbidden band,which reduces the bandgap ofα-Si3N4.展开更多
基金Project supported by the National Key Research and Development Program,China(Grant No.2016YFB0700503)the National High Technology Research and Development Program of China(Grant No.2015AA034201)+2 种基金the Beijing Science and Technology Plan,China(Grant No.D161100002416001)the National Natural Science Foundation of China(Grant No.51172018)the Kennametal Inc.,China
文摘The first-principles calculations are performed to investigate the structural, mechanical property, hardness, and electronic structure of WCoB with 0, 8.33, 16.67, 25, and 33.33 at.% Mn doping content and W_2 CoB_2 with 0, 10, and 20 at.%Mn doping content. The cohesive energy and formation energy indicate that all the structures can retain good structural stability. According to the calculated elastic constants, Mn is responsible for the increase of ductility and Poisson＇s ratio and the decrease of Young＇s modulus, shear modulus, and bulk modulus. By using the population analysis and mechanical properties, the hardness is characterized through using the five hardness models and is found to decrease with the Mn doping content increasing. The calculated electronic structure indicates that the formation of a B–Mn covalent bond and a W–Mn metallic bond contribute to the decreasing of the mechanical properties.
基金Project supported by the National Basic Research Program of China(Grant No.2011CB606401)
文摘Aiming at developing p-type semiconductors and modulating the band gap for photoelectronic devices and band engineering, we present the ab initio numerical simulation of the effect of codoping ZnO with Al, N and Mg on the crystal lattice and electronic structure. The simulations are based on the Perdew-Burke-Ernzerhof generalised-gradient approximation in density functional theory. Results indicate that electrons close to the Fermi level transfer effectively when Al, Mg, and N replace Zn and O atoms, and the theoretical results were consistent with the experiments. The addition of Mg leads to the variation of crystal lattice, expanse of energy band, and change of band gap. These unusual properties are explained in terms of the computed electronic structure, and the results show promise for the development of next-generation photoconducting devices in optoelectronic information science and technology.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11074039 and 11004032)the National Basic Research Program of China (Grant No. 2011CBA00200)
文摘Using first-principles calculations within the generalized gradient approximation （GGA） ＋U framework, we inves- tigate the effect of C doping on the structural and electronic properties of LiFePO4. The calculated formation energies indicate that C doped at O sites is energetically favoured, and that C dopants prefer to occupy 03 sites. The band gap of the C doped material is much narrow than that of the undoped one, indicating better electro- conductive properties. To maintain charge balance, the valence of the Fe nearest to C appears as Fe3＋, and it will be helpful to the hopping of electrons.
文摘The electronic structure and optical properties of pure, C-doped, C~ codoped and C-F-Be cluster- doped ZnO with a wurtzite structure were calculated by using the density functional theory with the plane-wave ultrasoft pseudopotentials method. The results indicate that p-type ZnO can be obtained by C incorporation, and the energy level of Co above the valence band maximum is 0.36 eV. The ionization energy of the complex Zn16O14CF and ZnlsBeO14CF can be reduced to 0.23 and 0.21 eV, individually. These results suggest that the defect complex of ZnlsBeO14CF is a better candidate for p-type ZnO. To make the optical properties clear, we investigated the imaginary part of the complex dielectric function ofundoped and C-F-Be doped ZnO. We found that there is strong absorption in the energy region lower than 2.7 eV for the C-F-Be doped system compared to pure ZnO.
基金This project was supported by the China Postdoctoral Science Foundation,Henan Postdoctoral Science Foundation,NCWU 2017 Annual Teaching Teacher Training Object ProjectKey Research Projects of Higher Education in Henan Province(18B150010)+1 种基金the Key Scientific Research Project of Henan Higher Education(No.17A520011)the Science and Technology Research Project of Henan Province(182102110029)
文摘Impurity formation energy, electronic structure, and photocatalytic properties of C-, N-, or S-doped BiOCl are investigated by density-functional theory plus U calculations(DFT + U). Results show that the doping effect of S is better than that of C or N on the tunable photocatalytic activities of BiOCl. At low concentration, S-doped BiOCl systems are the most stable under Bi-rich growth conditions because of their lower impurity-formation energy. Compared with the electronic structures of S-doped BiOCl, C-or N-doped BiOCl have relatively deeper impurity energy levels appearing in their band gap(except Bi_(36)O_(35)NCl_(36)), which may act as photogenerated carrier-recombination centers and reduce photocatalytic activity. At high concentration, S is substituted on the O lattice site system, whereas some S 3p states mix with the valence band; this mixture leads to an obvious band-gap decrease and continuum-state formation above the valence-band edge of BiOCl. Such activity is advantageous to photochemical catalysis response. Compared with pure Bi OCl and a low-concentration S-doped system, a high-concentration S-doped system shows an obvious redshift on the absorption edge and has better photocatalytic O_2 evolution performance.
基金supported by the National Natural Science Foundation of China(No.10775088)the Key Program of Theoretical Physics of Shandong Province
文摘Using the first-principles approach based upon the density functional theory （DFT）, we have studied the electronic structure of wurtzite ZnO systems doped with C at different sites. When Zn is substituted by C, the system turns from a direct band gap semiconductor into an indirect band gap semiconductor, and donor levels are formed. When O is substituted by C, acceptor levels are formed near the top of the valence band, and thus a p-type transformation of the system is achieved. When the two kinds of substitution coexist, the acceptor levels are compensated for all cases, which is unfavorable for the p-type transformation of the system.
基金Project supported by the National High Technology Research and Development Program of China (Grant No. 2009AA03Z405)the National Natural Science Foundation of China (Grant Nos. 60908028 and 60971068)the Chinese Universities Scientific Fund (Grant No. BUPT2009RC0412)
文摘We perform a first-principles simulation to study the electronic and optical properties of wurtzite Zn1-xCuxO. The simulations are based upon the Perdew-Burke-Ernzerhof form of generalised gradient approximation within the density functional theory. Calculations are carried out in different concentrations. With increasing Cu concentration, the band gap of Znl-xCuxO decreases due to the shift of valence band. The imaginary part of the dielectric function indicates that the optical transition between O2p states in the highest valence band and Zn 4s states in the lowest conduction band shifts to the low energy range as the Cu concentration increases. Besides, it is shown that the insertion of Cu atom leads to redshift of the optical absorption edge. Meanwhile, the optical constants of pure ZnO and Zn0.75Cu0.250, such as loss function, refractive index and reflectivity, are discussed.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51132002 and 11574261)the Natural Science Foundation of Hebei ProvinceChina(Grant No.A2015203261)
文摘The structures and electronic properties of ZnO nanowires（NWs） of different diameters are investigated by employing the first-principles density functional theory. The results indicate that the oxygen vacancy（VO） exerts a more evident influence on the band gap of the ZnO NWs. However, the effect will be weakened with the increase of the diameter. In addition, the energy band shifts downward due to the existence of VOand the offset decreases with the reduction of the VOconcentration. As the concentration of surface Zn atoms decreases, the conduction band shifts downward, while 2p electrons are lost in the oxygen vacancy, resulting in the split of valence band and the formation of an impurity level. Our findings agree well with the previous observations and will be of great importance for theoretical research based on ZnO NWs.
文摘Based on the experimental study of the optical properties of K2Ti6O13 doped with Fe or Ag,their electronic structures and optical properties are studied by the first-principles method based on the density functional theory（DFT）. The calculated optical properties are consistent with the experiment results. K2Ti6O13 doped with substitutional Fe or Ag has isolated impurity bands mainly stemming from the hybridization by the Fe 3d states or Ag 4d states with Ti 3d states and O 2p states and the band gap becomes narrower, the absorption edge of K2Ti6O13 thus has a clear red shift and the absorption of visible light can be realized after doping. For Fe-doped K2Ti6O13, the impurity bands are in the middle of the band gap, suggesting that they can be used as a bridge for valence band electrons transition to the conduction band. For Ag-doped K2Ti6O13,the impurity bands form a shallow acceptor above the valence band and can reduce the recombination rate of photoexcited carriers.The experimental and calculated results are significant for the development of K2Ti6O13materials that have absorption under visible light.
文摘Electronic structure and magnetic properties of wurtzite ZnO semiconductor doped with rare earth （RE=La, Ce, Pr, Pm, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb） atoms were studied using spin-polarized density functional theory based on the full-potential linear augmented plane wave （FP-LAPW） method as implemented in the Wien2k code. In this approach the generalized gradient approximation （GGA） was used for the exchange-correlation （XC） potential. Our results showed that the substitution of RE ions in ZnO induced spins polarized localized states in the band gap. Moreover, the studied DMSs compounds retained half metallicity at dopant concentration x=0.625%for most of the studied elements, with 100%spin polarization at the Fermi level （EF）. The total magnetic moments of these compounds existed due to RE 4f states present at EF, while small induced magnetic moments existed on other non-magnetic atoms as well. Finally, the energy difference between far and near configurations was investigated. It was found that the room temperature ferromagnetism was possible for RE-doped ZnO at near configuration. Since the RE-RE separation was long enough （far configuration） for magnetic coupling, the system became paramagnetic or antiferromagnetic ground state.
基金Funded by National Key Research and Development Program of China(No.2017YFB0310400)the National Natural Science Foundation of China(Nos.51872217,51932006,51972246 and 51521001)+3 种基金Fundamental Research Funds for the Central Universities in ChinaState Key Laboratory of Advanced Electromagnetic Engineering and Technology(Huazhong University of Science and Technology),the Joint Fund(No.6141A02022255)the Major Program of the Specialized Technological Innovation of HuBei Province,China(No.2019AFA176)the“111”Project(No.B13035)。
文摘We used density functional theory(DFT)calculations to study the influence of alkali earth metal element(AE)doping on the crystal structure and electronic band structure ofα-Si3N4.The diversity of atomic radii of alkaline earth metal elements results in structural expansion when they were doped into theα-Si3N4 lattice.Formation energies of the doped structures indicate that dopants prefer to occupy the interstitial site under the nitrogen-deficient environment,while substitute Si under the nitrogen-rich environment,which provides a guide to synthesizingα-Si3N4 with different doping types by controlling nitrogen conditions.For electronic structures,energy levels of the dopants appear in the bottom of the conduction band or the top of the valence band or the forbidden band,which reduces the bandgap ofα-Si3N4.
