The virial equation can well describe gas state at high temperature and pressure, but the difficulties in virial coefficient calculation limit the use of virial equation. Simple extended corresponding state principle(...The virial equation can well describe gas state at high temperature and pressure, but the difficulties in virial coefficient calculation limit the use of virial equation. Simple extended corresponding state principle(SE-CSP) is introduced in virial equation. Based on a corresponding state equation, including three characteristic parameters, an extended parameter is introduced to describe the second virial coefficient expressions of main products of propellant gas. The modified SE-CSP second virial coefficient expression was extrapolated based on the virial coefficients experimental temperature, and the second virial coefficients obtained are in good agreement with the experimental data at a low temperature and the theoretical values at high temperature. The maximum pressure in the closed bomb test was calculated with modified SE-CSP virial coefficient expressions with the calculated error of less than 2%, and the error was smaller than the result calculated with the reported values under the same calculation conditions. The modified SE-CSP virial coefficient expression provides a convenient and efficient method for practical virial coefficient calculation without resorting to complicated molecular model design and integral calculation.展开更多
In this article,we study the following Klein-Gordon-Maxwell system involving critical exponent■where λ and w are two positive constants.We found the existence of positive ground state solutions(that is,for solutions...In this article,we study the following Klein-Gordon-Maxwell system involving critical exponent■where λ and w are two positive constants.We found the existence of positive ground state solutions(that is,for solutions which minimizes the action functional among all the solutions)of(KGM) which improves some previous existence result in Carriao et al.(2012) [8].展开更多
In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu（100）, Cu（110）, and Cu（111） surfaces is obtained by first-principles calculations. The...In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu（100）, Cu（110）, and Cu（111） surfaces is obtained by first-principles calculations. The calculations indicate that relaxations mainly occur in the layers at which the surface states electrons are localized, and the magnitudes of the multilayer relaxations correspond to the difference of electron density of surface states between adjacent layers. The larger the interlayer relaxation is, the larger the difference of electron density of surface states between two layers is.展开更多
Using the first-principles plane-wave calculations within density functional theory, the perfect bi-layer and monolayer terminated WZ-CIS （100）/WZ-CdS （100） interfaces are investigated. After relaxation the atomic...Using the first-principles plane-wave calculations within density functional theory, the perfect bi-layer and monolayer terminated WZ-CIS （100）/WZ-CdS （100） interfaces are investigated. After relaxation the atomic positions and the bond lengths change slightly on the two interfaces. The WZ-CIS/WZ-CdS interfaces can exist stably, when the interface bonding energies are -0.481 J/m2 （bi-layer terminated interface） and -0.677 J/m2 （monolayer terminated interface）. Via analysis of the density of states, difference charge density and Bader charges, no interface state is found near the Fermi level. The stronger adhesion of the monolayer terminated interface is attributed to more electron transformations and orbital hybridizations, promoting stable interfacial bonds between atoms than those on a bi-layer terminated interface.展开更多
We have developed a computer code for {／em ab initio} the variational configuration interaction calculation of the electronic structure of atoms via variationally optimized Lagurre type orbitals, treating the orbital...We have developed a computer code for {／em ab initio} the variational configuration interaction calculation of the electronic structure of atoms via variationally optimized Lagurre type orbitals, treating the orbital effective charges as variational parameters. Excited states of the same symmetry, in order to avoid the inherent restrictions of the standard method of Hylleraas--Unheim and MacDonald, are computed variationally by minimizing the recently developed minimization functionals for excited states. By computing, at the minimum, the one-electron density and the probability distribution of the two-electron angle, and the most probable two-electron angle, we investigate the atomic states of the carbon atom. We show that, without resorting to the （admittedly unproven） concept of hybridization, as an intrinsic property of the atomic wave function, the most probable value of the two-electron angle is around the known angles of carbon bonding, i.e. either 109^／circ or 120^／circ or 180^／circ, depending on each low-lying state of the bare carbon atom.展开更多
Using first-principles calculations within density functional theory, we study the atomic structures and electronic properties of the perfect and defective （2VCu＋ Incu） CulnGaSe2/CdS interfaces theoretically, espec...Using first-principles calculations within density functional theory, we study the atomic structures and electronic properties of the perfect and defective （2VCu＋ Incu） CulnGaSe2/CdS interfaces theoretically, especially the interface states. We find that the local lattice structure of （2VCu＋ InCu） interface is somewhat disorganized. By analyzing the local density of states projected on several atomic layers of the two interfaces models, we find that for the （2VCu＋InCu） interface the interface states near the Fermi level in CulnGaSe2 and CdS band gap regions are mainly composed of interracial Se-4p, Cu-3d and S-3p orbitals, while for the perfect interface there are no clear interface states in the CulnGaSe2 region but only some interface states which are mainly composed of S-3p orbitals in the valance band of CdS region.展开更多
The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal struc...The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states （DOS） is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters （e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function） are calculated for the first time. The study of dielectric constant （ε1） indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values （DOS, Debye temperature, atomic mass, etc.） suggests that the compound is less likely to be superconductor.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 local crystal structures and electronic structures of LiMxFe1-xPO4 （M = Co, Ni, Rh） are studied through first-principles calculations. The lattice constants and unit cell volumes are smaller for the Co and Ni do...The local crystal structures and electronic structures of LiMxFe1-xPO4 （M = Co, Ni, Rh） are studied through first-principles calculations. The lattice constants and unit cell volumes are smaller for the Co and Ni doped materials than for pure LiFePO4, while larger than for the Rh doped material. The local structures around M atoms in the doped materials are studied in details. The total density of states （DOS） and atomic projected DOS （PDOS） are all calculated and analysed in detail. The results give a reasonable prediction to the improvement of electronic conductivity through Fe-site doping in LiFePO4 material.展开更多
We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity. We argue that these phenomena are possible because o...We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity. We argue that these phenomena are possible because of the robustness of many-body quantum states with respect to the external environment, which is directly related to the uncertainty principle as applied to coordinates and momenta of the carriers. In the case of superconductors, this implies relationships between macroscopic quantities such as critical temperature and critical magnetic field, and microscopic quantities such as the amount of spatial squeezing of a Cooper pair and its correlation time. In the case of ultracold atomic Fermi gases, this should be paralleled by a connection between the critical temperature for the onset of superfluidity and the corresponding critical velocity. Tests of this conjecture are finally sketched with particular regard to the understanding of the behaviour of superconductors under external pressures or mesoscopic superconductors, and the possibility to mimic these effects in ultracold atomic Fermi gases using Feshbach resonances and atomic squeezed states.展开更多
This paper deals with maximum principle for some optimal control problem governed by some elliptic variational inequalities. Some state constraints are discussed. The basic techniques used here are based on those in [...This paper deals with maximum principle for some optimal control problem governed by some elliptic variational inequalities. Some state constraints are discussed. The basic techniques used here are based on those in [1] and a new penalty functional defined in this paper.展开更多
We have made a first principles study to investigate density of states, band structure, the dielectric function and absorption spectra of wurtzite Mg0.25Zn0.75O. The calculation is carried out in a-axis and c-axis str...We have made a first principles study to investigate density of states, band structure, the dielectric function and absorption spectra of wurtzite Mg0.25Zn0.75O. The calculation is carried out in a-axis and c-axis strain changing in the range from 0.3 to -0.2 in intervals of 0.1. The results calculated from density of states show that the bottom of conduction band is always dominated by Zn 4s and the top of valence band is always dominated by O 2p in a-axis and c-axis strain. Zn 4s will shift to higher energy range when a-axis strain changes in the range from 0.3 to 0, and then shift to lower energy range when a-axis strain changes in the range from 0 to -0.2. But Zn 4s will always shift to higher energy range when c-axis strain changes in the range from 0.3 to -0.2. The variations of band gap calculated from band structure and absorption spectra are also investigated, which are consistent with the results obtained from density of states. In addition, we analyse and discuss the imaginary part of the dielectric function ε2.展开更多
A detailed study of the M_3N_4（M = Si,Ge,Sn） nitrides in their tetragonal,monoclinic and orthorhombic phases has been performed with the plane-wave pseudo-potential method combined with the quasi-harmonic approximat...A detailed study of the M_3N_4（M = Si,Ge,Sn） nitrides in their tetragonal,monoclinic and orthorhombic phases has been performed with the plane-wave pseudo-potential method combined with the quasi-harmonic approximation,including the phononic effects.We rationalize the main puzzle,i.e.,the fundamental properties of these phases are unclear,by calculating the crystal structures,density of states,and optical properties.The direct band gaps of t-Ge_3N_4,m-Si_3N_4,and o-Ge_3N_4 benefit the opto-electrical properties,t-,m-,and o-Si_3N_4 can be used as refractive materials while m-M_3N_4（M = Si,Ge,Sn） are optically transparent in the visible light region.Our results improve the understanding of the detailed electronic structures of all compounds,as well as the influences of electronic structure on their stabilities.Furthermore,we find that thermodynamic quantities are sensitive to structures and,therefore,depend on various temperature and pressure conditions.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
Combining first-principles calculations with the particle swarm optimization （PSO） algorithm, we have explored the ground-state structure of Pd2N, whose structure is in debate although it is the first synthesized bi...Combining first-principles calculations with the particle swarm optimization （PSO） algorithm, we have explored the ground-state structure of Pd2N, whose structure is in debate although it is the first synthesized binary platinum group nitride. The ground-state structure is predicted to be tetragonal with space group P^-4m2, which is energetically more favorable than the previously proposed orthorhombic Co2N-type structure. The stability is confirmed by the subsequent calculations on the phonon dispersion curves and elastic constants. Furthermore, the calculated mechanical properties indicate that Pd2N has low incompressibility and is a common hard material.展开更多
Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO i...Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is su- perior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majority- spin A1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin A1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin Al state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance （TMR） value under large biaxial strain. This work reveals the internal mechanism for the state coupling al strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel .junctions with high tunneling magnetoresistance effect.展开更多
文摘The virial equation can well describe gas state at high temperature and pressure, but the difficulties in virial coefficient calculation limit the use of virial equation. Simple extended corresponding state principle(SE-CSP) is introduced in virial equation. Based on a corresponding state equation, including three characteristic parameters, an extended parameter is introduced to describe the second virial coefficient expressions of main products of propellant gas. The modified SE-CSP second virial coefficient expression was extrapolated based on the virial coefficients experimental temperature, and the second virial coefficients obtained are in good agreement with the experimental data at a low temperature and the theoretical values at high temperature. The maximum pressure in the closed bomb test was calculated with modified SE-CSP virial coefficient expressions with the calculated error of less than 2%, and the error was smaller than the result calculated with the reported values under the same calculation conditions. The modified SE-CSP virial coefficient expression provides a convenient and efficient method for practical virial coefficient calculation without resorting to complicated molecular model design and integral calculation.
基金partially supported by the National Natural Science Foundation of China(11801400,11571187)partially supported by the National Natural Science Foundation of China(11861053)the Postdoctoral Science Foundation of China(2017M611159)
文摘In this article,we study the following Klein-Gordon-Maxwell system involving critical exponent■where λ and w are two positive constants.We found the existence of positive ground state solutions(that is,for solutions which minimizes the action functional among all the solutions)of(KGM) which improves some previous existence result in Carriao et al.(2012) [8].
基金Project substantially supported by the National Natural Science Foundation of China （Grant No 60471034） and partially by the National Natural Science Foundation of China and the Science Foundation of China Academy of Engineering Physics （Grant No 10576004）.
文摘In this paper the relationship between the surface relaxations and the electron density distributions of surface states of Cu（100）, Cu（110）, and Cu（111） surfaces is obtained by first-principles calculations. The calculations indicate that relaxations mainly occur in the layers at which the surface states electrons are localized, and the magnitudes of the multilayer relaxations correspond to the difference of electron density of surface states between adjacent layers. The larger the interlayer relaxation is, the larger the difference of electron density of surface states between two layers is.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11164014 and 11364025)the Gansu Science and Technology Pillar Program,China(Grant No.1204GKCA057)
文摘Using the first-principles plane-wave calculations within density functional theory, the perfect bi-layer and monolayer terminated WZ-CIS （100）/WZ-CdS （100） interfaces are investigated. After relaxation the atomic positions and the bond lengths change slightly on the two interfaces. The WZ-CIS/WZ-CdS interfaces can exist stably, when the interface bonding energies are -0.481 J/m2 （bi-layer terminated interface） and -0.677 J/m2 （monolayer terminated interface）. Via analysis of the density of states, difference charge density and Bader charges, no interface state is found near the Fermi level. The stronger adhesion of the monolayer terminated interface is attributed to more electron transformations and orbital hybridizations, promoting stable interfacial bonds between atoms than those on a bi-layer terminated interface.
基金supported by the National High Technology Research and Development Program of China (Grant No. 2004AA306H10)the operational program "Competitiveness" of the Greek General Secretariat of Research and Technology(Grant No. 04EP111/ENTEP-2004)
文摘We have developed a computer code for {／em ab initio} the variational configuration interaction calculation of the electronic structure of atoms via variationally optimized Lagurre type orbitals, treating the orbital effective charges as variational parameters. Excited states of the same symmetry, in order to avoid the inherent restrictions of the standard method of Hylleraas--Unheim and MacDonald, are computed variationally by minimizing the recently developed minimization functionals for excited states. By computing, at the minimum, the one-electron density and the probability distribution of the two-electron angle, and the most probable two-electron angle, we investigate the atomic states of the carbon atom. We show that, without resorting to the （admittedly unproven） concept of hybridization, as an intrinsic property of the atomic wave function, the most probable value of the two-electron angle is around the known angles of carbon bonding, i.e. either 109^／circ or 120^／circ or 180^／circ, depending on each low-lying state of the bare carbon atom.
基金supported by the National Natural Science Foundation of China(Grant Nos.11364025 and 11164014)the Gansu Science and Technology PillarProgram,China(Grant No.1204GKCA057)
文摘Using first-principles calculations within density functional theory, we study the atomic structures and electronic properties of the perfect and defective （2VCu＋ Incu） CulnGaSe2/CdS interfaces theoretically, especially the interface states. We find that the local lattice structure of （2VCu＋ InCu） interface is somewhat disorganized. By analyzing the local density of states projected on several atomic layers of the two interfaces models, we find that for the （2VCu＋InCu） interface the interface states near the Fermi level in CulnGaSe2 and CdS band gap regions are mainly composed of interracial Se-4p, Cu-3d and S-3p orbitals, while for the perfect interface there are no clear interface states in the CulnGaSe2 region but only some interface states which are mainly composed of S-3p orbitals in the valance band of CdS region.
文摘The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states （DOS） is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters （e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function） are calculated for the first time. The study of dielectric constant （ε1） indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values （DOS, Debye temperature, atomic mass, etc.） suggests that the compound is less likely to be superconductor.
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.
基金Project supported by the National Natural Science Foundation of China （Grant Nos 10604023 and 10564002）, the Natural Science Foundation of Jiangxi Province （Grant No 0512017）, the Science Foundation of Jiangxi Provincial Education Department （Grant No GJJ[2005]73）, and Science Foundation of Zhejiang Sci-Tech University （Grant No 0613271-Y）.
文摘The local crystal structures and electronic structures of LiMxFe1-xPO4 （M = Co, Ni, Rh） are studied through first-principles calculations. The lattice constants and unit cell volumes are smaller for the Co and Ni doped materials than for pure LiFePO4, while larger than for the Rh doped material. The local structures around M atoms in the doped materials are studied in details. The total density of states （DOS） and atomic projected DOS （PDOS） are all calculated and analysed in detail. The results give a reasonable prediction to the improvement of electronic conductivity through Fe-site doping in LiFePO4 material.
文摘We discuss the general interplay between the uncertainty principle and the onset of dissipationless transport phenomena such as superconductivity and superfluidity. We argue that these phenomena are possible because of the robustness of many-body quantum states with respect to the external environment, which is directly related to the uncertainty principle as applied to coordinates and momenta of the carriers. In the case of superconductors, this implies relationships between macroscopic quantities such as critical temperature and critical magnetic field, and microscopic quantities such as the amount of spatial squeezing of a Cooper pair and its correlation time. In the case of ultracold atomic Fermi gases, this should be paralleled by a connection between the critical temperature for the onset of superfluidity and the corresponding critical velocity. Tests of this conjecture are finally sketched with particular regard to the understanding of the behaviour of superconductors under external pressures or mesoscopic superconductors, and the possibility to mimic these effects in ultracold atomic Fermi gases using Feshbach resonances and atomic squeezed states.
文摘This paper deals with maximum principle for some optimal control problem governed by some elliptic variational inequalities. Some state constraints are discussed. The basic techniques used here are based on those in [1] and a new penalty functional defined in this paper.
基金supported by doctor start-up fund of Bohai University (Grant No KJ2007005)
文摘We have made a first principles study to investigate density of states, band structure, the dielectric function and absorption spectra of wurtzite Mg0.25Zn0.75O. The calculation is carried out in a-axis and c-axis strain changing in the range from 0.3 to -0.2 in intervals of 0.1. The results calculated from density of states show that the bottom of conduction band is always dominated by Zn 4s and the top of valence band is always dominated by O 2p in a-axis and c-axis strain. Zn 4s will shift to higher energy range when a-axis strain changes in the range from 0.3 to 0, and then shift to lower energy range when a-axis strain changes in the range from 0 to -0.2. But Zn 4s will always shift to higher energy range when c-axis strain changes in the range from 0.3 to -0.2. The variations of band gap calculated from band structure and absorption spectra are also investigated, which are consistent with the results obtained from density of states. In addition, we analyse and discuss the imaginary part of the dielectric function ε2.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61475132 and 61501392)
文摘A detailed study of the M_3N_4（M = Si,Ge,Sn） nitrides in their tetragonal,monoclinic and orthorhombic phases has been performed with the plane-wave pseudo-potential method combined with the quasi-harmonic approximation,including the phononic effects.We rationalize the main puzzle,i.e.,the fundamental properties of these phases are unclear,by calculating the crystal structures,density of states,and optical properties.The direct band gaps of t-Ge_3N_4,m-Si_3N_4,and o-Ge_3N_4 benefit the opto-electrical properties,t-,m-,and o-Si_3N_4 can be used as refractive materials while m-M_3N_4（M = Si,Ge,Sn） are optically transparent in the visible light region.Our results improve the understanding of the detailed electronic structures of all compounds,as well as the influences of electronic structure on their stabilities.Furthermore,we find that thermodynamic quantities are sensitive to structures and,therefore,depend on various temperature and pressure conditions.
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.
基金Project supported by the Science Foundation of Baoji University of Arts and Sciences,China(Grants Nos.ZK11061,ZK11135,and ZK12048)the Natural Science Foundation of the Education Committee of Shaanxi Province,China(Grant Nos.2013JK0637 and 2013JK0638)the Natural Science Basic Research Plan in Shaanxi Province,China(Grant No.2013JQ1007)
文摘Combining first-principles calculations with the particle swarm optimization （PSO） algorithm, we have explored the ground-state structure of Pd2N, whose structure is in debate although it is the first synthesized binary platinum group nitride. The ground-state structure is predicted to be tetragonal with space group P^-4m2, which is energetically more favorable than the previously proposed orthorhombic Co2N-type structure. The stability is confirmed by the subsequent calculations on the phonon dispersion curves and elastic constants. Furthermore, the calculated mechanical properties indicate that Pd2N has low incompressibility and is a common hard material.
基金Project supported by the National Key Research and Development Program of China(Grant No.2016YFB0400801)the National Natural Science Foundation of China(Grant Nos.61774128,61674124,11604275,11304257,and 61227009)+1 种基金the Natural Science Foundation of Fujian Province of China(Grant Nos.2017J01012,2014J01026,2016J01037,and 2015J01028)the Fundamental Research Funds for the Central Universities,China(Grant Nos.20720150027,20720160044,20720160122,20720170085,20720170012,and 20720150033)
文摘Electronic structure and spin-related state coupling at ferromagnetic material （FM）/MgO （FM = Fe, CoFe, CoFeB） interfaces under biaxial strain are evaluated using the first-principles calculations. The CoFeB/MgO interface, which is su- perior to the Fe/MgO and CoFe/MgO interfaces, can markedly maintain stable and effective coupling channels for majority- spin A1 state under large biaxial strain. Bonding interactions between Fe, Co, and B atoms and the electron transfer between Bloch states are responsible for the redistribution of the majority-spin A1 state, directly influencing the coupling effect for the strained interfaces. Layer-projected wave function of the majority-spin Al state suggests slower decay rate and more stable transport property in the CoFeB/MgO interface, which is expected to maintain a higher tunneling magnetoresistance （TMR） value under large biaxial strain. This work reveals the internal mechanism for the state coupling al strained FM/MgO interfaces. This study may provide some references to the design and manufacturing of magnetic tunnel .junctions with high tunneling magnetoresistance effect.
