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 electronic structure,elasticity,and magnetic properties of the Mn_(2)XIn(X=Fe,Co)full-Heusler compounds are comprehensively investigated via first-principles calculations.The calculated elastic constants indicate ...The electronic structure,elasticity,and magnetic properties of the Mn_(2)XIn(X=Fe,Co)full-Heusler compounds are comprehensively investigated via first-principles calculations.The calculated elastic constants indicate that both Mn_(2)FeIn and Mn_(2)Co In possess ductility.At the optimal lattice constants,the magnetic moments are found to be 1.40μB/f.u.for Mn_(2)FeIn and 1.69μB/f.u.for Mn_(2)CoIn.Under the biaxial strain ranging from-2%to 5%,Mn_(2)FeIn demonstrates a remarkable variation in the spin polarization,spanning from-2%to 74%,positioning it as a promising candidate for applications in spintronic devices.Analysis of the electronic structure reveals that the change in spin polarization under strain is due to the shift of the spin-down states at the Fermi surface.Additionally,under biaxial strain,the magnetic anisotropy of Mn_(2)FeIn undergoes a transition of easy-axis direction.Utilizing second-order perturbation theory and electronic structure analysis,the variation in magnetic anisotropy with strain can be attributed to changes of d-orbital states near the Fermi surface.展开更多
Thework presents the electronic structure computations and optical spectroscopy studies of half-Heusler ScNiBi and YNiBi compounds.Our first-principles computations of the electronic structures were based on density f...Thework presents the electronic structure computations and optical spectroscopy studies of half-Heusler ScNiBi and YNiBi compounds.Our first-principles computations of the electronic structures were based on density functional theory accounting for spin-orbit coupling.These compounds are computed to be semiconductors.The calculated gap values make ScNiBi and YNiBi valid for thermoelectric and optoelectronic applications and as selective filters.In ScNiBi and YNiBi,an intense peak at the energy of−2 eV is composed of theNi 3d states in the conduction band,and the valence band mostly contains these states with some contributions from the Bi 6p and Sc 3d or Y 4d electronic states.These states participate in the formation of the indirect gap of 0.16 eV(ScNiBi)and 0.18 eV(YNiBi).Within the spectral ellipsometry technique in the interval 0.22–15μm of wavelength,the optical functions of materials are studied,and their dispersion features are revealed.A good matching of the experimental and modeled optical conductivity spectra allowed us to analyze orbital contributions.The abnormally low optical absorption observed in the low-energy region of the spectrum is referred to as the results of band calculations indicating a small density of electronic states near the Fermi energy of these complex materials.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
SnTe has received considerable attention as an environmentally friendly alternative to the representative thermoelectric material of PbTe.However,excessive hole carrier concentration in SnTe results in an extremely lo...SnTe has received considerable attention as an environmentally friendly alternative to the representative thermoelectric material of PbTe.However,excessive hole carrier concentration in SnTe results in an extremely low Seebeck coefficient and high thermal conductivity,which makes it exhibit relatively inferior thermoelectric properties.In this work,the thermoelectric performance of p-type SnTe is enhanced through regulating its energy band structures and reducing its electronic thermal conductivity by combining Bi doping with CdSe alloying.First,the carrier concentration of SnTe is successfully suppressed via Bi doping,which significantly decreases the electronic thermal conductivity.Then,the convergence and flattening of the valence bands by alloying CdSe effectively improves the effective mass of SnTe while restraining its carrier mobility.Finally,a maximum figure of merit(ZT) of~ 0.87 at 823 K and an average ZT of~ 0.51 at 300-823 K have been achieved in Sn_(0.96)Bi_(0.04)Te-5%CdSe.Our results indicate that decreasing the electronic thermal conductivity is an effective means of improving the performance of thermoelectric materials with a high carrier concentration.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
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
Understanding pressure-regulated electronic properties is crucial for integrating two-dimensional semiconductors into flexible electronic devices and pressure sensors. We thoroughly explored the tunability of the elec...Understanding pressure-regulated electronic properties is crucial for integrating two-dimensional semiconductors into flexible electronic devices and pressure sensors. We thoroughly explored the tunability of the electronic structure of monolayer MoS_(2) upon the application of perpendicular pressure and shear stress by using first-principles calculations. The band gap increased at low pressures and then decreased as the pressure increased.Variations in the band gap are caused by the combined interaction of the increasing and decreasing trends in the band gap. The increase in the band gap is induced by the enhancement of the p–d orbital interaction at the top of the valence band(TVB). The delocalization of charge and unstable hybridization bonding causes a reduction in the band gap. The band gap under perpendicular pressure modes is closely related to the structural variation. Shear stress can effectively reduce the band gap with minimal change to the crystal structure. The maximum point at the TVB and the minimum point at the bottom of the conduction band are different for all pressure modes, resulting in various anisotropic properties. This study provides a theoretical basis for modulating the electrical and optical properties of monolayer MoS_(2).展开更多
Band structure and bonding properties have been investigated in terms of periodic density functional theory（DFT） method,and two-photon absorption（TPA） spectra have been simulated by two-band model for ZnGeP2 and A...Band structure and bonding properties have been investigated in terms of periodic density functional theory（DFT） method,and two-photon absorption（TPA） spectra have been simulated by two-band model for ZnGeP2 and AgGaS2 crystals.It has been predicted that the AgGaS2 crystal has a wider window of nonlinear transmission,and the laser pumping energy larger than 1.02 and 1.35 eV will lead to deleterious TPA of higher nonlinear effect for ZnGeP2 and AgGaS2 crystals,respectively.Electron origin of TPA for them is also discussed.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
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
Recently,Lee et al.claimed the experimental discovery of room-temperature ambient-pressure super-conductivity in a Cu-doped lead-apatite(LK-99)(arXiv:2307.12008,arXiv:2307.12037).Remarkably,the claimed superconductivi...Recently,Lee et al.claimed the experimental discovery of room-temperature ambient-pressure super-conductivity in a Cu-doped lead-apatite(LK-99)(arXiv:2307.12008,arXiv:2307.12037).Remarkably,the claimed superconductivity can persist up to 400 K at ambient pressure.Despite the experimental im-plication,the electronic structure of LK-99 has not yet been studied.Here,we investigate the electronic structures of LK-99 and its parent compound using first-principles calculations,aiming to elucidate the doping effects of Cu.Our results reveal that the parent compound Pb_(10)(PO_(4))_(6)O is an insulator,while Cu doping induces an insulator-metal transition and thus volume contraction.The band structures of LK-99 around the Fermi level are featured by a half-filled flat band and a fully-occupied flat band.These two very flat bands arise from both the 2p orbitals of 1/4-occupied O atoms and the hybridization of the 3d orbitals of Cu with the 2p orbitals of its nearest-neighboring O atoms.Interestingly,we observe four van Hove singularities on these two flat bands.Furthermore,we show that the flat band structures can be tuned by including electronic correlation effects or by doping different elements.We find that among the considered doping elements(Ni,Cu,Zn,Ag,and Au),both Ni and Zn doping result in the gap opening,whereas Au exhibits doping effects more similar to Cu than Ag.Our work establishes a foundation for fu-ture studies to investigate the role of unique electronic structures of LK-99 in its claimed superconducting properties.展开更多
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Project supported by the Fundamental Research Funds for the Provincial Universities of Zhejiang Province,China(Grant No.GK229909299001-05)Zhejiang Provincial Public Welfare Projects of China(Grant No.LGG22F030017)。
文摘The electronic structure,elasticity,and magnetic properties of the Mn_(2)XIn(X=Fe,Co)full-Heusler compounds are comprehensively investigated via first-principles calculations.The calculated elastic constants indicate that both Mn_(2)FeIn and Mn_(2)Co In possess ductility.At the optimal lattice constants,the magnetic moments are found to be 1.40μB/f.u.for Mn_(2)FeIn and 1.69μB/f.u.for Mn_(2)CoIn.Under the biaxial strain ranging from-2%to 5%,Mn_(2)FeIn demonstrates a remarkable variation in the spin polarization,spanning from-2%to 74%,positioning it as a promising candidate for applications in spintronic devices.Analysis of the electronic structure reveals that the change in spin polarization under strain is due to the shift of the spin-down states at the Fermi surface.Additionally,under biaxial strain,the magnetic anisotropy of Mn_(2)FeIn undergoes a transition of easy-axis direction.Utilizing second-order perturbation theory and electronic structure analysis,the variation in magnetic anisotropy with strain can be attributed to changes of d-orbital states near the Fermi surface.
文摘Thework presents the electronic structure computations and optical spectroscopy studies of half-Heusler ScNiBi and YNiBi compounds.Our first-principles computations of the electronic structures were based on density functional theory accounting for spin-orbit coupling.These compounds are computed to be semiconductors.The calculated gap values make ScNiBi and YNiBi valid for thermoelectric and optoelectronic applications and as selective filters.In ScNiBi and YNiBi,an intense peak at the energy of−2 eV is composed of theNi 3d states in the conduction band,and the valence band mostly contains these states with some contributions from the Bi 6p and Sc 3d or Y 4d electronic states.These states participate in the formation of the indirect gap of 0.16 eV(ScNiBi)and 0.18 eV(YNiBi).Within the spectral ellipsometry technique in the interval 0.22–15μm of wavelength,the optical functions of materials are studied,and their dispersion features are revealed.A good matching of the experimental and modeled optical conductivity spectra allowed us to analyze orbital contributions.The abnormally low optical absorption observed in the low-energy region of the spectrum is referred to as the results of band calculations indicating a small density of electronic states near the Fermi energy of these complex materials.
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financially supported by the National Natural Science Foundation of China (Nos.52102234 and 51972094)the High-level Talents Research Initiation Project of Hebei University (No.521000981421)Hebei Province Introduced Overseas Student Funding Project (No.C20210313)。
文摘SnTe has received considerable attention as an environmentally friendly alternative to the representative thermoelectric material of PbTe.However,excessive hole carrier concentration in SnTe results in an extremely low Seebeck coefficient and high thermal conductivity,which makes it exhibit relatively inferior thermoelectric properties.In this work,the thermoelectric performance of p-type SnTe is enhanced through regulating its energy band structures and reducing its electronic thermal conductivity by combining Bi doping with CdSe alloying.First,the carrier concentration of SnTe is successfully suppressed via Bi doping,which significantly decreases the electronic thermal conductivity.Then,the convergence and flattening of the valence bands by alloying CdSe effectively improves the effective mass of SnTe while restraining its carrier mobility.Finally,a maximum figure of merit(ZT) of~ 0.87 at 823 K and an average ZT of~ 0.51 at 300-823 K have been achieved in Sn_(0.96)Bi_(0.04)Te-5%CdSe.Our results indicate that decreasing the electronic thermal conductivity is an effective means of improving the performance of thermoelectric materials with a high carrier concentration.
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.
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the National Key R&D Program of China(No.2019YFB2204500)Shenzhen Science and Technology Program(No.KQTD20180412181422399)+2 种基金the Science and Technology Innovation Commission of Shenzhen(Nos.JCYJ20180507181858539 and JCYJ20190808173815205)the National Natural Science Foundation of China(Nos.11575074,11975006 and 51804199)the Natural Science Foundation of Guangdong Province(No.2019A1515012111)。
文摘Understanding pressure-regulated electronic properties is crucial for integrating two-dimensional semiconductors into flexible electronic devices and pressure sensors. We thoroughly explored the tunability of the electronic structure of monolayer MoS_(2) upon the application of perpendicular pressure and shear stress by using first-principles calculations. The band gap increased at low pressures and then decreased as the pressure increased.Variations in the band gap are caused by the combined interaction of the increasing and decreasing trends in the band gap. The increase in the band gap is induced by the enhancement of the p–d orbital interaction at the top of the valence band(TVB). The delocalization of charge and unstable hybridization bonding causes a reduction in the band gap. The band gap under perpendicular pressure modes is closely related to the structural variation. Shear stress can effectively reduce the band gap with minimal change to the crystal structure. The maximum point at the TVB and the minimum point at the bottom of the conduction band are different for all pressure modes, resulting in various anisotropic properties. This study provides a theoretical basis for modulating the electrical and optical properties of monolayer MoS_(2).
基金Supported by the National Natural Science Foundation of China (No. 20373073)the National Basic Research Program of China (No. 2007CB815307)+1 种基金the Funds of Chinese Academy of Sciences (KJCX2-YW-H01)Fujian Key Laboratory of Nanomaterials (No. 2006L2005)
文摘Band structure and bonding properties have been investigated in terms of periodic density functional theory（DFT） method,and two-photon absorption（TPA） spectra have been simulated by two-band model for ZnGeP2 and AgGaS2 crystals.It has been predicted that the AgGaS2 crystal has a wider window of nonlinear transmission,and the laser pumping energy larger than 1.02 and 1.35 eV will lead to deleterious TPA of higher nonlinear effect for ZnGeP2 and AgGaS2 crystals,respectively.Electron origin of TPA for them is also discussed.
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.
文摘Recently,Lee et al.claimed the experimental discovery of room-temperature ambient-pressure super-conductivity in a Cu-doped lead-apatite(LK-99)(arXiv:2307.12008,arXiv:2307.12037).Remarkably,the claimed superconductivity can persist up to 400 K at ambient pressure.Despite the experimental im-plication,the electronic structure of LK-99 has not yet been studied.Here,we investigate the electronic structures of LK-99 and its parent compound using first-principles calculations,aiming to elucidate the doping effects of Cu.Our results reveal that the parent compound Pb_(10)(PO_(4))_(6)O is an insulator,while Cu doping induces an insulator-metal transition and thus volume contraction.The band structures of LK-99 around the Fermi level are featured by a half-filled flat band and a fully-occupied flat band.These two very flat bands arise from both the 2p orbitals of 1/4-occupied O atoms and the hybridization of the 3d orbitals of Cu with the 2p orbitals of its nearest-neighboring O atoms.Interestingly,we observe four van Hove singularities on these two flat bands.Furthermore,we show that the flat band structures can be tuned by including electronic correlation effects or by doping different elements.We find that among the considered doping elements(Ni,Cu,Zn,Ag,and Au),both Ni and Zn doping result in the gap opening,whereas Au exhibits doping effects more similar to Cu than Ag.Our work establishes a foundation for fu-ture studies to investigate the role of unique electronic structures of LK-99 in its claimed superconducting properties.
