Electronic structures and optical properties of single-layer In1-xGaxN are studied by employ-ing Heyd-Scuseria-Ernzerh(HSE)method based on the first-principles.The band structure and density of states(DOS)of single-la...Electronic structures and optical properties of single-layer In1-xGaxN are studied by employ-ing Heyd-Scuseria-Ernzerh(HSE)method based on the first-principles.The band structure and density of states(DOS)of single-layer In1-xGaxN are calculated,and the band gap ranges from 1.8 eV to 3.8 eV as the ratio x changes,illustrating the potential for the tun-ability of band gap values via Ga doped.We also have investigated optical properties of single-layer In1-xGaxN such as dielectric function,refractive index and absorption coeficient,the main peak of dielectric function spectrum and the absorption edge are found to have a remarkable blue-shift as the concentration of Ga increases.Furthermore,the optical properties of single-layer In1-xGaxN are analyzed based on the band structures and DOS analysis.Such unique optical properties have profound application in nanoelectronics and optical devices.展开更多
The Eu-doped Cu(In, Eu)Te2 semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical...The Eu-doped Cu(In, Eu)Te2 semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical properties than those of CuInTe2. In this paper, the Eu-doped CuInTe2 (CuIn1-xEuxTe2, x = 0, 0.1, 0.2, 0.3) are studied systemically based on the empirical electron theory (EET). The studies cover crystal structures, bonding regularities, cohesive energies, energy levels, and valence electron structures. The theoretical values fit the experimental results very well. The physical mechanism of a broadened band-gap induced by Eu doping into CuInTe2 is the transitions between different hybridization energy levels induced by electron hopping between s and d orbitals and the transformations from the lattice electrons to valence electrons for Cu and In ions. The research results reveal that the photovoltaic effect induces the increase of lattice electrons of In and causes the electric resistivity to decrease. The Eu doping into CuInTe2 mainly influences the transition between different hybridization energy levels for Cu atoms, which shows that the 3d electron numbers of Cu atoms change before and after Eu doping. In single phase CuIn1-xEuxTe2, the number of valence electrons changes regularly with increasing Eu content, and the calculated band gap Eg also increases, which implies that the optical properties of Eu-doped CuIn1-xEuxTe2 are improved.展开更多
The energy band properties, density of states, and band alignment of the BexZn1-xO1-ySy alloy (Be- and S-doped wurtzite ZnO) are investigated by the first-principles method. BexZn1-xO1-ySy alloy is a direct band gap...The energy band properties, density of states, and band alignment of the BexZn1-xO1-ySy alloy (Be- and S-doped wurtzite ZnO) are investigated by the first-principles method. BexZn1-xO1-ySy alloy is a direct band gap semiconductor, the valence band maximum (VBM) and the conduction band minimum (CBM) of BexZn1-xO1-ySy are dominated by S 3p and Zn 4s states, respectively. The band gap and lattice constant of BexZn1-xO1-ySy alloy can be modulated by changing the doped content values x and y. With the increase in Be content value x in the BexZnl-xOl-ySy alloy, the band gap increases and the lattice constant reduces, but the situation is just the opposite when increasing the S content value y in the BexZn1-xO1-ySy alloy. Because the lattice constant of Be0.375Zn0.625O0.75S0.25 alloy is well matched with that of ZnO and its energy gap is large compared with that of ZnO, so the Be0.375Zn0.625O0.75S0.25 alloy is suitable for serving as the blocking material for a high-quality ZnO-based device.展开更多
In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3A...In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/ Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly fiat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the "Flat/steep" band model than to the van-Hove singularity scenario. The fiat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.展开更多
The tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA) has been used to calculate structural and electronic properties of thallium pnictides TlX (X = Sb, Bi). As a fu...The tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA) has been used to calculate structural and electronic properties of thallium pnictides TlX (X = Sb, Bi). As a function of volume, the total energy is evaluated. Apart from this, equilibrium lattice parameter, bulk modulus, first order derivative, electronic and lattice heat co-efficient, Debye temperature and Grüneisen constants, band structure and density of states are calculated. From energy band diagram, we observed metallic behaviour in TlSb and TlBi compounds. The equilibrium lattice constants agreed well with the available data.展开更多
he present paper covers thedectronic structure of Molybdenite(MoS_2)with layer structure studied using tight-binding energy band structure calculation and localization molecular orbital CNDO/2 method,and the bonding c...he present paper covers thedectronic structure of Molybdenite(MoS_2)with layer structure studied using tight-binding energy band structure calculation and localization molecular orbital CNDO/2 method,and the bonding characters of Mo-- Mo,S--S and Mo==Satomic pairs in MoS_2 crystal are discussed.展开更多
The structural, elastic and electronic properties of YAg-B2(CsCl) were investigated using the first-principles calculations. The energy band structure and the density of states were studied in detail, including part...The structural, elastic and electronic properties of YAg-B2(CsCl) were investigated using the first-principles calculations. The energy band structure and the density of states were studied in detail, including partial density of states (PDOS), in order to identify the character of each band. The structural parameters (lattice constant, bulk modulus, pressure derivative of bulk modulus) and elastic constants were also obtained. The results were consistent with the experimental data available in the literature, as well as other theoretical results.展开更多
Iron-based superconductor family FeX(X=S,Se,Te)has been one of the research foci in physics and material science due to their record-breaking superconducting temperature(FeSe film)and rich physical phenomena.Recently,...Iron-based superconductor family FeX(X=S,Se,Te)has been one of the research foci in physics and material science due to their record-breaking superconducting temperature(FeSe film)and rich physical phenomena.Recently,FeS,the least studied Fe X compound(due to the difficulty in synthesizing high quality macroscopic crystals)attracted much attention because of its puzzling superconducting pairing symmetry.In this work,combining scanning tunneling microscopy and angle resolved photoemission spectroscopy(ARPES)with sub-micron spatial resolution,we investigate the intrinsic electronic structures of superconducting FeS from individual single crystalline domains.Unlike FeTe or FeSe,FeS remains identical tetragonal structure from room temperature down to 5 K,and the band structures observed can be well reproduced by our ab-initio calculations.Remarkably,mixed with the 1×1 tetragonal metallic phase,we also observe the coexistence of √5×√5 reconstructed insulating phase in the crystal,which not only helps explain the unusual properties of FeS,but also demonstrates the importance of using spatially resolved experimental tools in the study of this compound.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
We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system ...We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system CeCoIn5.Multiple Fermi surface sheets and a complex band structure are clearly resolved. We have also performed detailed band structure calculations on CePt2In7. The good agreement found between our measurements and the calculations suggests that the band renormalization effect is rather weak in CePt2In7. A comparison of the common features of the electronic structure of CePt2In7and CeCoIn5indicates that CeCoIn5shows a much stronger band renormalization effect than CePt2In7. These results provide new information for understanding the heavy fermion behaviors and unconventional superconductivity in Ce-based heavy fermion systems.展开更多
With the help of ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculating the electronic structure and linear optical properties is carried out for XCd2(SO4)3 (X =Tl, Rb). The result...With the help of ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculating the electronic structure and linear optical properties is carried out for XCd2(SO4)3 (X =Tl, Rb). The results show that Tl2Cd2(SO4)3 (TlCdS) has a larger band gap than Rb2Cd2(SO4)3 (RbCdS) and the energy bands for RbCdS are more dispersive than those of TlCdS. From their partial densities of states (PDOS), we have observed that the hybridization between S ionic 2p and O atomic 2p orbitals forms SO4 ionic groups. The remarkable difference between RbCdS and TlCdS is, however, the degree of hybridization between cation (Tl and Rb) and its surrounding oxygen atoms. In the view of quantum chemistry, the strong p-d hybridization indicates the existence of their cation ionic bonds (Cd-O, Rb-O, and Tl-O). The calculations of TlCdS and RbCdS show their optical properties to be less anisotropic. Their anisotropies in the optical properties mainly occur in a low photon energy region of 5-16 eV.展开更多
With the help of the ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculations of the electronic structure and linear optical properties are carried out for red HgI2 and yellow HgI2. It ...With the help of the ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculations of the electronic structure and linear optical properties are carried out for red HgI2 and yellow HgI2. It is found that the red HgI2 has a direct gap of 1.22834 eV and the yellow HgI2 has an indirect gap of 2.11222 eV. For the red HgI2, the calculated optical spectra are qualitatively in agreement with the experimental data. Furthermore, the origins of the different peaks of ε2(ω) are discussed. Our calculated anisotropic dielectric function of the red HgI2 is a nice match with the experimental results. Our calculated results are able to reproduce the overall trend of the experimental reflectivity spectra. Although no comparable experimental and theoretical results are available, clearly, the above proves the reliability of our calculations, suggesting that our calculations should be convincing for the yellow HgI2. Finally, the different optical properties are discussed.展开更多
Lattice constants and electronic structures of diluted magnetic semiconductors ( In, Mn ) As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrati...Lattice constants and electronic structures of diluted magnetic semiconductors ( In, Mn ) As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrations of the 3 d impurities were studied ( x = 1/2, 1/4, 1/8). The effect of varying Mn coucentrations on the lattice constants and the electronic structures are shown.展开更多
The electronic structural, effective masses of carriers, and optical properties of pure and La-doped Cd2SnO4 are calculated by using the first-principles method based on the density functional theory. Using the GGA+U...The electronic structural, effective masses of carriers, and optical properties of pure and La-doped Cd2SnO4 are calculated by using the first-principles method based on the density functional theory. Using the GGA+U method, we show that Cd2SnO4 is a direct band-gap semiconductor with a band gap of 2.216 eV, the band gap decreases to 2.02 eV and the Fermi energy level moves to the conduction band after La doping. The density of states of Cd2SnO4 shows that the bottom of the conduction band is composed of Cd 5s, Sn 5s, and Sn 5p orbits, the top of the valence band is composed of Cd 4d and O 2p, and the La 5d orbital is hybridized with the O 2p orbital, which plays a key role at the conduction band bottom after La doping. The effective masses at the conduction band bottom of pure and La-doped Cd2SnO4 are 0.18m0 and 0.092m0, respectively, which indicates that the electrical conductivity of Cd2SnO4 after La doping is improved. The calculated optical properties show that the optical transmittance of La-doped Cd2SnO4 is 92%, the optical absorption edge is slightly blue shifted, and the optical band gap is increased to 3.263 eV. All the results indicate that the conductivity and optical transmittance of Cd2SnO4 can be improved by doping La.展开更多
Crystals of Ba3ZnSb2O9 have been grown by a high-temperature solid-state reaction and characterized by single-crystal X-ray diffraction.Ba3ZnSb2O9 crystallizes in the hexagonal P63/mmc space group with a = 5.8663(4)...Crystals of Ba3ZnSb2O9 have been grown by a high-temperature solid-state reaction and characterized by single-crystal X-ray diffraction.Ba3ZnSb2O9 crystallizes in the hexagonal P63/mmc space group with a = 5.8663(4),c = 14.478(2) ,V = 431.49(8) 3,Z = 2 and R(all data) = 0.0167.The structure of Ba3ZnSb2O9 consists of pairs of face-sharing Sb2O9 bi-octahedra connected via corners with two single layers of mutually isolated ZnO6 octahedra.Each Ba2+ ion is bonded to 12 oxygen atoms.The UV-vis absorption spectrum of the compound has been investigated.Additionally,the calculations of band structure and density of states have also been performed with density functional theory method.The obtained results tend to support the experimental data of the absorption spectrum.展开更多
Three kinds of metal atoms with different valence electronic configurations,Bi(6s^(2)6p^(3)),Y(4d^(1)5s^(2)),and Ce(4f^(1)5d^(1)6s^(2)),were selected to investigate the effect of A-site(La^(3+))doping on electronic ba...Three kinds of metal atoms with different valence electronic configurations,Bi(6s^(2)6p^(3)),Y(4d^(1)5s^(2)),and Ce(4f^(1)5d^(1)6s^(2)),were selected to investigate the effect of A-site(La^(3+))doping on electronic band structure,photoelectric properties,and photocatalytic performance of LaFeO_(3) perovskite.It was identified that the Bi doped LaFeO_(3) presented significantly improved photocatalytic activity towards the reduction of CO_(2),while the Y or Ce doped LaFeO_(3) displayed decreased photocatalytic activity compared to the pristine LaFeO_(3).It was revealed that doping of all the three metal atoms resulted in narrowed band gap and thus extended light absorption of LaFeO_(3) by lowering its conduction band minimum(CBM).The recombination rate and mobility of the charge carriers were represented by the relative effective mass(D)between holes and electrons for pristine and A-site doped LaFeO_(3).The doping of Bi resulted in increased D value,attributed to the Bi 6s electron states at the valence band maximum(VBM),and thus promoted separation and transfer of the charge carriers and improved photocatalytic activity of LaFeO_(3).In contrast,the doping of Ce resulted in significantly decreased D value,induced by the highly localized Ce 4f hole states at the CBM,and thus higher recombination rate of the charge carriers and decreased photocatalytic activity of LaFeO_(3).Furthermore,the Y doped LaFeO_(3) with a slightly decreased D value presented slightly increased recombination rate of the charge carriers and thus decreased photocatalytic activity.Such a work provides new insights into the A-site doping in LaFeO_(3) perovskite,which should be helpful for optimizing the electronic band structure and activity of perovskite-type photocatalysts at atomic level.展开更多
The electronic structures of TiAl-2M(M=V, Nb, Ta, Cr, Mo, W,Mn) alloy have been investigated using EHT band calculation method. Their bandstructures and average prperties have been obtained. The results show that dopi...The electronic structures of TiAl-2M(M=V, Nb, Ta, Cr, Mo, W,Mn) alloy have been investigated using EHT band calculation method. Their bandstructures and average prperties have been obtained. The results show that doping thetransition metal elements can effectively change the band structure and enable the alloysystem to show the stronger metallic feature. The dopants of V, Cr and Mn increase s-orbital component of Ti and Al in bonding orbital, therefore, there is more sphericalelectronic clound and weakly directional bonds in the crystal, which improve the duictil-ity of the alloy, Nb or Ta makes stronger bonding with Ti and Al, which improvestrength and oxidation resistance of the alloy.展开更多
The structural, energetic, and electronic properties of lattice highly mismatched ZnY1-xOx (Y = S, Se, Te) ternary alloys with dilute O concentrations are calculated from first principles within the density function...The structural, energetic, and electronic properties of lattice highly mismatched ZnY1-xOx (Y = S, Se, Te) ternary alloys with dilute O concentrations are calculated from first principles within the density functional theory. We demonstrate the formation of an isolated intermediate electronic band structure through diluted O-substitute in zinc-blende ZnY (Y = S, Se, Te) at octahedral sites in a semiconductor by the calculations of density of states (DOS), leading to a significant absorption below the band gap of the parent semiconductor and an enhancement of the optical absorption in the whole energy range of the solar spectrum. It is found that the intermediate band states should be described as a result of the coupling between impurity O 2p states with the conduction band states. Moreover, the intermediate bands (IBs) in ZnTeO show high stabilization with the change of O concentration resulting from the largest electronegativity difference between O and Te compared with in the other ZnSO and ZnSeO.展开更多
基金supported by the National Natural Science Foundation of China (No.11404230)Foundation of Science and Technology Bureau of Sichuan Province (No.2013JY0085)
文摘Electronic structures and optical properties of single-layer In1-xGaxN are studied by employ-ing Heyd-Scuseria-Ernzerh(HSE)method based on the first-principles.The band structure and density of states(DOS)of single-layer In1-xGaxN are calculated,and the band gap ranges from 1.8 eV to 3.8 eV as the ratio x changes,illustrating the potential for the tun-ability of band gap values via Ga doped.We also have investigated optical properties of single-layer In1-xGaxN such as dielectric function,refractive index and absorption coeficient,the main peak of dielectric function spectrum and the absorption edge are found to have a remarkable blue-shift as the concentration of Ga increases.Furthermore,the optical properties of single-layer In1-xGaxN are analyzed based on the band structures and DOS analysis.Such unique optical properties have profound application in nanoelectronics and optical devices.
基金supported by the National Natural Science Foundation of China(Grant No.1 1274110)
文摘The Eu-doped Cu(In, Eu)Te2 semiconductors with chalcopyrite structures are promising materials for their applications in the absorption layer for thin-film solar cells due to their wider band-gaps and better optical properties than those of CuInTe2. In this paper, the Eu-doped CuInTe2 (CuIn1-xEuxTe2, x = 0, 0.1, 0.2, 0.3) are studied systemically based on the empirical electron theory (EET). The studies cover crystal structures, bonding regularities, cohesive energies, energy levels, and valence electron structures. The theoretical values fit the experimental results very well. The physical mechanism of a broadened band-gap induced by Eu doping into CuInTe2 is the transitions between different hybridization energy levels induced by electron hopping between s and d orbitals and the transformations from the lattice electrons to valence electrons for Cu and In ions. The research results reveal that the photovoltaic effect induces the increase of lattice electrons of In and causes the electric resistivity to decrease. The Eu doping into CuInTe2 mainly influences the transition between different hybridization energy levels for Cu atoms, which shows that the 3d electron numbers of Cu atoms change before and after Eu doping. In single phase CuIn1-xEuxTe2, the number of valence electrons changes regularly with increasing Eu content, and the calculated band gap Eg also increases, which implies that the optical properties of Eu-doped CuIn1-xEuxTe2 are improved.
基金supported by the National Natural Science Foundation of China(Grant No.61078046)the Special Funds for Provincial Strategic and Emerging Industries Projects of Guangdong Province,China(Grant No.2012A080304016)the Youth Foundation of South China Normal University,China(Grant No.2012KJ018)
文摘The energy band properties, density of states, and band alignment of the BexZn1-xO1-ySy alloy (Be- and S-doped wurtzite ZnO) are investigated by the first-principles method. BexZn1-xO1-ySy alloy is a direct band gap semiconductor, the valence band maximum (VBM) and the conduction band minimum (CBM) of BexZn1-xO1-ySy are dominated by S 3p and Zn 4s states, respectively. The band gap and lattice constant of BexZn1-xO1-ySy alloy can be modulated by changing the doped content values x and y. With the increase in Be content value x in the BexZnl-xOl-ySy alloy, the band gap increases and the lattice constant reduces, but the situation is just the opposite when increasing the S content value y in the BexZn1-xO1-ySy alloy. Because the lattice constant of Be0.375Zn0.625O0.75S0.25 alloy is well matched with that of ZnO and its energy gap is large compared with that of ZnO, so the Be0.375Zn0.625O0.75S0.25 alloy is suitable for serving as the blocking material for a high-quality ZnO-based device.
基金financially supported by the Science Foundation for International Cooperation of Sichuan Province (2014HH0016)the Fundamental Research Funds for the Central Universities (SWJTU2014: A0920502051113-10000)National Magnetic Confinement Fusion Science Program (2011GB112001)
文摘In this work, we choose Nb3Al/Nb3Sn as a new test case for flat/steep band model of superconductivity. Based on the density functional theory in the generalized gradient approximation, the electronic structure of Nb3Al/ Nb3Sn has been studied. The obtained results agree well with those of the earlier studies and show clearly fiat bands around the Fermi level. The steep bands as characterized in this work locate around the M point in the first Brillouin zone. The obtained results reveal that Nb3Al/Nb3Sn fits more to the "Flat/steep" band model than to the van-Hove singularity scenario. The fiat/steep band condition for superconductivity implies a different thermodynamic behavior of superconductors other than that predicted from the conventional BCS theory. This observation sets up an indicator for selecting a suitable superconductor when its large-scale industrial use is needed, for example, in superconducting maglev system or ITER project.
文摘The tight binding linear muffin-tin-orbital (TB-LMTO) method within the local density approximation (LDA) has been used to calculate structural and electronic properties of thallium pnictides TlX (X = Sb, Bi). As a function of volume, the total energy is evaluated. Apart from this, equilibrium lattice parameter, bulk modulus, first order derivative, electronic and lattice heat co-efficient, Debye temperature and Grüneisen constants, band structure and density of states are calculated. From energy band diagram, we observed metallic behaviour in TlSb and TlBi compounds. The equilibrium lattice constants agreed well with the available data.
文摘he present paper covers thedectronic structure of Molybdenite(MoS_2)with layer structure studied using tight-binding energy band structure calculation and localization molecular orbital CNDO/2 method,and the bonding characters of Mo-- Mo,S--S and Mo==Satomic pairs in MoS_2 crystal are discussed.
基金supported by Gazi University Research Project Unit (05/2007/18)Hacettepe University (0701602005)
文摘The structural, elastic and electronic properties of YAg-B2(CsCl) were investigated using the first-principles calculations. The energy band structure and the density of states were studied in detail, including partial density of states (PDOS), in order to identify the character of each band. The structural parameters (lattice constant, bulk modulus, pressure derivative of bulk modulus) and elastic constants were also obtained. The results were consistent with the experimental data available in the literature, as well as other theoretical results.
基金Project supported by CAS-Shanghai Science Research Center,China(Grant No.CAS-SSRC-YH-2015-01)the National Key R&D Program of China(Grant No.2017YFA0305400)+4 种基金the National Natural Science Foundation of China(Grant Nos.11674229,11227902,and 11604207)the EPSRC Platform Grant(Grant No.EP/M020517/1)Hefei Science Center,Chinese Academy of Sciences(Grant No.2015HSC-UE013)Science and Technology Commission of Shanghai Municipality,China(Grant No.14520722100)the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB04040200)。
文摘Iron-based superconductor family FeX(X=S,Se,Te)has been one of the research foci in physics and material science due to their record-breaking superconducting temperature(FeSe film)and rich physical phenomena.Recently,FeS,the least studied Fe X compound(due to the difficulty in synthesizing high quality macroscopic crystals)attracted much attention because of its puzzling superconducting pairing symmetry.In this work,combining scanning tunneling microscopy and angle resolved photoemission spectroscopy(ARPES)with sub-micron spatial resolution,we investigate the intrinsic electronic structures of superconducting FeS from individual single crystalline domains.Unlike FeTe or FeSe,FeS remains identical tetragonal structure from room temperature down to 5 K,and the band structures observed can be well reproduced by our ab-initio calculations.Remarkably,mixed with the 1×1 tetragonal metallic phase,we also observe the coexistence of √5×√5 reconstructed insulating phase in the crystal,which not only helps explain the unusual properties of FeS,but also demonstrates the importance of using spatially resolved experimental tools in the study of this compound.
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The ARPES experimental work is supported by the National Natural Science Foundation of China(Grant No.11574360)the National Basic Research Program of China(Grant Nos.2015CB921300,2013CB921700,and 2013CB921904)+3 种基金the Strategic Priority Research Program(B)of the Chinese Academy of Sciences(Grant No.XDB07020300)supported by the National Natural Science Foundation of China(Grant No.91421304)the Fundamental Research Funds for the Central Universities of Chinathe Research Funds of Renmin University of China(Grant Nos.14XNLQ03 and16XNLQ01)
文摘We have carried out high-resolution angle-resolved photoemission measurements on the Ce-based heavy fermion compound CePt2In7that exhibits stronger two-dimensional character than the prototypical heavy fermion system CeCoIn5.Multiple Fermi surface sheets and a complex band structure are clearly resolved. We have also performed detailed band structure calculations on CePt2In7. The good agreement found between our measurements and the calculations suggests that the band renormalization effect is rather weak in CePt2In7. A comparison of the common features of the electronic structure of CePt2In7and CeCoIn5indicates that CeCoIn5shows a much stronger band renormalization effect than CePt2In7. These results provide new information for understanding the heavy fermion behaviors and unconventional superconductivity in Ce-based heavy fermion systems.
基金Project supported by the National Science Foundation of China (Grant No 2006CB921605) and the National Natural Science Foundation of China (Grant Nos 10174024 and 10474025).
文摘With the help of ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculating the electronic structure and linear optical properties is carried out for XCd2(SO4)3 (X =Tl, Rb). The results show that Tl2Cd2(SO4)3 (TlCdS) has a larger band gap than Rb2Cd2(SO4)3 (RbCdS) and the energy bands for RbCdS are more dispersive than those of TlCdS. From their partial densities of states (PDOS), we have observed that the hybridization between S ionic 2p and O atomic 2p orbitals forms SO4 ionic groups. The remarkable difference between RbCdS and TlCdS is, however, the degree of hybridization between cation (Tl and Rb) and its surrounding oxygen atoms. In the view of quantum chemistry, the strong p-d hybridization indicates the existence of their cation ionic bonds (Cd-O, Rb-O, and Tl-O). The calculations of TlCdS and RbCdS show their optical properties to be less anisotropic. Their anisotropies in the optical properties mainly occur in a low photon energy region of 5-16 eV.
基金Project supported by Program for Science and Technology Innovation Talents in Universities of Henan Province,China (Grant No. 2008HASTIT008)the National Natural Science Foundation of China (Grant No. 10574039)the Key Project Foundation of Science and Technology of He’nan Province,China (Grant No. 092102210166)
文摘With the help of the ab initio full-potential linearized augmented plane wave (FPLAPW) method, calculations of the electronic structure and linear optical properties are carried out for red HgI2 and yellow HgI2. It is found that the red HgI2 has a direct gap of 1.22834 eV and the yellow HgI2 has an indirect gap of 2.11222 eV. For the red HgI2, the calculated optical spectra are qualitatively in agreement with the experimental data. Furthermore, the origins of the different peaks of ε2(ω) are discussed. Our calculated anisotropic dielectric function of the red HgI2 is a nice match with the experimental results. Our calculated results are able to reproduce the overall trend of the experimental reflectivity spectra. Although no comparable experimental and theoretical results are available, clearly, the above proves the reliability of our calculations, suggesting that our calculations should be convincing for the yellow HgI2. Finally, the different optical properties are discussed.
基金Funded by the National Natural Science Foundation of China(No.60476047) ,the Key Teacher Foundation of the EducationalBureau of Henan Province ,and the Natural Science Foundation ofthe Educational Bureau of Henan Province , China ( No:2003140027 ,2004140004)
文摘Lattice constants and electronic structures of diluted magnetic semiconductors ( In, Mn ) As were investigated using the first principles LMTO-ASA band calculation by assuming supercell structures. Three concentrations of the 3 d impurities were studied ( x = 1/2, 1/4, 1/8). The effect of varying Mn coucentrations on the lattice constants and the electronic structures are shown.
文摘The electronic structural, effective masses of carriers, and optical properties of pure and La-doped Cd2SnO4 are calculated by using the first-principles method based on the density functional theory. Using the GGA+U method, we show that Cd2SnO4 is a direct band-gap semiconductor with a band gap of 2.216 eV, the band gap decreases to 2.02 eV and the Fermi energy level moves to the conduction band after La doping. The density of states of Cd2SnO4 shows that the bottom of the conduction band is composed of Cd 5s, Sn 5s, and Sn 5p orbits, the top of the valence band is composed of Cd 4d and O 2p, and the La 5d orbital is hybridized with the O 2p orbital, which plays a key role at the conduction band bottom after La doping. The effective masses at the conduction band bottom of pure and La-doped Cd2SnO4 are 0.18m0 and 0.092m0, respectively, which indicates that the electrical conductivity of Cd2SnO4 after La doping is improved. The calculated optical properties show that the optical transmittance of La-doped Cd2SnO4 is 92%, the optical absorption edge is slightly blue shifted, and the optical band gap is increased to 3.263 eV. All the results indicate that the conductivity and optical transmittance of Cd2SnO4 can be improved by doping La.
基金Supported by the National Natural Science Foundation of China (No. 20773131)the National Basic Research Program of China (No. 2007CB815307)Fujian Key Laboratory of Nanomaterials (No. 2006L2005)
文摘Crystals of Ba3ZnSb2O9 have been grown by a high-temperature solid-state reaction and characterized by single-crystal X-ray diffraction.Ba3ZnSb2O9 crystallizes in the hexagonal P63/mmc space group with a = 5.8663(4),c = 14.478(2) ,V = 431.49(8) 3,Z = 2 and R(all data) = 0.0167.The structure of Ba3ZnSb2O9 consists of pairs of face-sharing Sb2O9 bi-octahedra connected via corners with two single layers of mutually isolated ZnO6 octahedra.Each Ba2+ ion is bonded to 12 oxygen atoms.The UV-vis absorption spectrum of the compound has been investigated.Additionally,the calculations of band structure and density of states have also been performed with density functional theory method.The obtained results tend to support the experimental data of the absorption spectrum.
基金supported by the National Natural Science Foundation of China(No.21773089).
文摘Three kinds of metal atoms with different valence electronic configurations,Bi(6s^(2)6p^(3)),Y(4d^(1)5s^(2)),and Ce(4f^(1)5d^(1)6s^(2)),were selected to investigate the effect of A-site(La^(3+))doping on electronic band structure,photoelectric properties,and photocatalytic performance of LaFeO_(3) perovskite.It was identified that the Bi doped LaFeO_(3) presented significantly improved photocatalytic activity towards the reduction of CO_(2),while the Y or Ce doped LaFeO_(3) displayed decreased photocatalytic activity compared to the pristine LaFeO_(3).It was revealed that doping of all the three metal atoms resulted in narrowed band gap and thus extended light absorption of LaFeO_(3) by lowering its conduction band minimum(CBM).The recombination rate and mobility of the charge carriers were represented by the relative effective mass(D)between holes and electrons for pristine and A-site doped LaFeO_(3).The doping of Bi resulted in increased D value,attributed to the Bi 6s electron states at the valence band maximum(VBM),and thus promoted separation and transfer of the charge carriers and improved photocatalytic activity of LaFeO_(3).In contrast,the doping of Ce resulted in significantly decreased D value,induced by the highly localized Ce 4f hole states at the CBM,and thus higher recombination rate of the charge carriers and decreased photocatalytic activity of LaFeO_(3).Furthermore,the Y doped LaFeO_(3) with a slightly decreased D value presented slightly increased recombination rate of the charge carriers and thus decreased photocatalytic activity.Such a work provides new insights into the A-site doping in LaFeO_(3) perovskite,which should be helpful for optimizing the electronic band structure and activity of perovskite-type photocatalysts at atomic level.
文摘The electronic structures of TiAl-2M(M=V, Nb, Ta, Cr, Mo, W,Mn) alloy have been investigated using EHT band calculation method. Their bandstructures and average prperties have been obtained. The results show that doping thetransition metal elements can effectively change the band structure and enable the alloysystem to show the stronger metallic feature. The dopants of V, Cr and Mn increase s-orbital component of Ti and Al in bonding orbital, therefore, there is more sphericalelectronic clound and weakly directional bonds in the crystal, which improve the duictil-ity of the alloy, Nb or Ta makes stronger bonding with Ti and Al, which improvestrength and oxidation resistance of the alloy.
基金Project supported by the State Key Program for Basic Research of China (Grant No.2011CB302003)the Project of High Technology Research and Development Program of China (Grant No.2007AA03Z404)+1 种基金the National Natural Science Foundation of China (Grant Nos.60990312,61274058,61025020,and 61073101)the Natural Science Foundation of Anhui Province,China (Grant No.1208085QF116)
文摘The structural, energetic, and electronic properties of lattice highly mismatched ZnY1-xOx (Y = S, Se, Te) ternary alloys with dilute O concentrations are calculated from first principles within the density functional theory. We demonstrate the formation of an isolated intermediate electronic band structure through diluted O-substitute in zinc-blende ZnY (Y = S, Se, Te) at octahedral sites in a semiconductor by the calculations of density of states (DOS), leading to a significant absorption below the band gap of the parent semiconductor and an enhancement of the optical absorption in the whole energy range of the solar spectrum. It is found that the intermediate band states should be described as a result of the coupling between impurity O 2p states with the conduction band states. Moreover, the intermediate bands (IBs) in ZnTeO show high stabilization with the change of O concentration resulting from the largest electronegativity difference between O and Te compared with in the other ZnSO and ZnSeO.