The analytical expression of the electronic density of states (DOS) for single-walled carbon nanotubes (SWNTs) has been derived on the basis of graphene approximation of the energy E(k) near the Fermi level EF. The di...The analytical expression of the electronic density of states (DOS) for single-walled carbon nanotubes (SWNTs) has been derived on the basis of graphene approximation of the energy E(k) near the Fermi level EF. The distinctive properties of the DOS, the normalized differential conductivity and the current us bias for SWNTs are deduced and analyzed theoretically. The singularities in the DOS (or in the normalized differential conductivity) predict that the jump structure of current (or conductance)-bias of SWNTs exists. All conclusions from the theoretical analysis are in well agreement with the experimental results of SWNT's electronic structure and electronic transport. In other words, the simple theoretical model in this paper can be applied to understand a range of spectroscopic and other measurement data related to the DOS of SWNTs.展开更多
The electronic structures of cubic structure of ABX3（A=CH3NH3, Cs; B=Sn, Pb; X=Cl, Br, I） are analyzed by den- sity functional theory using the Perdew-Burke-Ernzerhof exchange-correlation functional and using the He...The electronic structures of cubic structure of ABX3（A=CH3NH3, Cs; B=Sn, Pb; X=Cl, Br, I） are analyzed by den- sity functional theory using the Perdew-Burke-Ernzerhof exchange-correlation functional and using the Heyd-Scuseria- Ernzerhof hybrid functional. The valence band maximum （VBM） is found to be made up by an antibonding hybridization of B s and X p states, whereas bands made up by the π antibonding of B p and X p states dominates the conduction band minimum （CBM）. The changes of VBM, CBM, and band gap with ion B and X are then systematically summarized. The natural band offsets of ABX3 are partly given. We also found for all the ABX3 perovskite materials in this study, the bandgap increases with an increasing lattice parameter. This phenomenon has good consistency with the experimental results.展开更多
The lowest total energy crystal structure of Li2MgN2H2 was identified by the first principle calculation with RPBE exchange-correlation function. Furthermore, the fine structure parameters of this crystal structure we...The lowest total energy crystal structure of Li2MgN2H2 was identified by the first principle calculation with RPBE exchange-correlation function. Furthermore, the fine structure parameters of this crystal structure were calculated with PBE and PW91 exchange-correlation function. In a further step, the density of states, electron density, charge density difference on (0 0 1) plane and heat of formation of Li2MgN2H2 hydrogenation were computed with PW91 exchange-correlation function. Consequently, the electronic structures and chemical bonds in this compound were analyzed and discussed, and then the thermodynamic character of Li2MgN2H2 for hydrogen storage was evacuated.展开更多
The electronic structure and magnetism of compound Nd\-2Fe 17 N\-3 has been studied with MS_Xα method. It was found that there are negative exchange couplings between Fe(f) and Fe(c) atoms in Nd\-2Fe 17 N x compounds...The electronic structure and magnetism of compound Nd\-2Fe 17 N\-3 has been studied with MS_Xα method. It was found that there are negative exchange couplings between Fe(f) and Fe(c) atoms in Nd\-2Fe 17 N x compounds. The interstitial N atoms make the unit cell volume of the compounds increase a little, and hence the strength of negative exchange coupling decreases.展开更多
Comprehensive first-principles calculations are performed to provide insight into the intriguing physical properties of the ternary cubic fluoride KCrF3. The electronic structures exhibit a prominent dependence on the...Comprehensive first-principles calculations are performed to provide insight into the intriguing physical properties of the ternary cubic fluoride KCrF3. The electronic structures exhibit a prominent dependence on the effective local Coulomb interaction parameter Ueff. The ground state of the cubic phase is a ferromagnetic （FM） half-metal with Ueff equal to 0, 2, and 4 eV, whereas the insulating A-type antiferromagnetic （A-AFM） state with concomitant homogeneous orbital ordering is more robust than the FM state for Ueff exceeding 4 eV. We propose that the origin of the orbital ordering is purely electronic when the cooperative Jahn-Teller distortions are absent in cubic KCrF3.展开更多
基金The work is financially supported by the National Natural Science Foundation of China (No.59972031)and the Scientific Research Fund of Hunan Provincial Education Department (No.01C248). Authors wish to express their sincere appreciation to these sponsors
文摘The analytical expression of the electronic density of states (DOS) for single-walled carbon nanotubes (SWNTs) has been derived on the basis of graphene approximation of the energy E(k) near the Fermi level EF. The distinctive properties of the DOS, the normalized differential conductivity and the current us bias for SWNTs are deduced and analyzed theoretically. The singularities in the DOS (or in the normalized differential conductivity) predict that the jump structure of current (or conductance)-bias of SWNTs exists. All conclusions from the theoretical analysis are in well agreement with the experimental results of SWNT's electronic structure and electronic transport. In other words, the simple theoretical model in this paper can be applied to understand a range of spectroscopic and other measurement data related to the DOS of SWNTs.
基金supported by the National Natural Science Foundation of China(Grant No.11375112)
文摘The electronic structures of cubic structure of ABX3（A=CH3NH3, Cs; B=Sn, Pb; X=Cl, Br, I） are analyzed by den- sity functional theory using the Perdew-Burke-Ernzerhof exchange-correlation functional and using the Heyd-Scuseria- Ernzerhof hybrid functional. The valence band maximum （VBM） is found to be made up by an antibonding hybridization of B s and X p states, whereas bands made up by the π antibonding of B p and X p states dominates the conduction band minimum （CBM）. The changes of VBM, CBM, and band gap with ion B and X are then systematically summarized. The natural band offsets of ABX3 are partly given. We also found for all the ABX3 perovskite materials in this study, the bandgap increases with an increasing lattice parameter. This phenomenon has good consistency with the experimental results.
文摘The lowest total energy crystal structure of Li2MgN2H2 was identified by the first principle calculation with RPBE exchange-correlation function. Furthermore, the fine structure parameters of this crystal structure were calculated with PBE and PW91 exchange-correlation function. In a further step, the density of states, electron density, charge density difference on (0 0 1) plane and heat of formation of Li2MgN2H2 hydrogenation were computed with PW91 exchange-correlation function. Consequently, the electronic structures and chemical bonds in this compound were analyzed and discussed, and then the thermodynamic character of Li2MgN2H2 for hydrogen storage was evacuated.
文摘The electronic structure and magnetism of compound Nd\-2Fe 17 N\-3 has been studied with MS_Xα method. It was found that there are negative exchange couplings between Fe(f) and Fe(c) atoms in Nd\-2Fe 17 N x compounds. The interstitial N atoms make the unit cell volume of the compounds increase a little, and hence the strength of negative exchange coupling decreases.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11104101 and 11004073)the Scientific and Technologic Research Program of Department of Education of Hubei Province,China(Grant No.D20132902)
文摘Comprehensive first-principles calculations are performed to provide insight into the intriguing physical properties of the ternary cubic fluoride KCrF3. The electronic structures exhibit a prominent dependence on the effective local Coulomb interaction parameter Ueff. The ground state of the cubic phase is a ferromagnetic （FM） half-metal with Ueff equal to 0, 2, and 4 eV, whereas the insulating A-type antiferromagnetic （A-AFM） state with concomitant homogeneous orbital ordering is more robust than the FM state for Ueff exceeding 4 eV. We propose that the origin of the orbital ordering is purely electronic when the cooperative Jahn-Teller distortions are absent in cubic KCrF3.
