The electronic structure,including band structure,density of states （DOS）, and partial density of states of SrTi1-xSbxO3 with x = 0,0. 125,0.25,and 0.33 is calculated from the first principles of plane wave ultra-so...The electronic structure,including band structure,density of states （DOS）, and partial density of states of SrTi1-xSbxO3 with x = 0,0. 125,0.25,and 0.33 is calculated from the first principles of plane wave ultra-soft pseudo-potential technology based on density function theory. The calculated results reveal that due to the electron doping,the Fermi level moves into the conduction bands for SrTi1-xSbxO3 with x = 0. 125 and the system shows metallic behavior. In addition, the DOS moves towards low energy and the optical band gap is broadened. The wide band gap and the low density of the states in the conduction band result in the transparency of the films.展开更多
We have investigated properties of the compound LuAlO3：Ce^3＋ associated with the Ce^3＋ 4f-5d transition by using the periodic density functional theory. A hybrid functional has been used for the 4f states and a con...We have investigated properties of the compound LuAlO3：Ce^3＋ associated with the Ce^3＋ 4f-5d transition by using the periodic density functional theory. A hybrid functional has been used for the 4f states and a constrained approach has been employed for the excited 5d state. It is found that the average distance between Ce^3＋ and the eight nearest-neighbor O atoms decrease by 0.05 A on going from 4f to 5d state. The calculated Stokes shift is in good agreement with experiment. Based on the optimized structure around Ce^3＋, the energy level scheme of the 5d states has been evaluated using the angular overlap model, in reasonable agreement with experiment.展开更多
A model system consisting of Ni[001]（100）/Ni3Al[001]（100） multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation ...A model system consisting of Ni[001]（100）/Ni3Al[001]（100） multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ′＋2γto 10γ′＋10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer＇s thickness. A Ni/Ni3Al multilayer with 10γ′＋10γ atomic layers （3.54 nm） can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young＇s modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ′ phase volume fraction are calculated by varying the proportion of the γ and γ′ phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures.展开更多
The structural,electronic and optical properties of KNbO 3 （KN）,NaNbO3（NN）and K05 Na0.5NbO3（KNN） in paraelectric cubic phase were calculated employing the plane-wave pseudopotential method based on density funct...The structural,electronic and optical properties of KNbO 3 （KN）,NaNbO3（NN）and K05 Na0.5NbO3（KNN） in paraelectric cubic phase were calculated employing the plane-wave pseudopotential method based on density functional theory （DFT）.The calculated electronic structures of the three crystals show similar features in the valence bands and the lower conduction bands.However,the structures in higher conduction bands differ markedly due to the effect of Na and K atoms.The calculated optical properties reveal that the features of optical spectrum at low energy are dominated by the transitions from O2p valence bands to Nb 4d conduction bands and those at high energy are related to the transitions to K 4s4p and/or Na 3s3p states.Moreover,the optical constants of KNN are approximately the average of KN and NN at high energy.Therefore,the optical properties of KNN in high energy region can probably be altered by changing the ratio of Na/K.展开更多
Elastic properties of three high pressure polymorphs of CaCO_3 are investigated based on first principles calculations.The calculations are conducted at 0 GPa–40 GPa for aragonite, 40 GPa–65 GPa for post-aragonite, ...Elastic properties of three high pressure polymorphs of CaCO_3 are investigated based on first principles calculations.The calculations are conducted at 0 GPa–40 GPa for aragonite, 40 GPa–65 GPa for post-aragonite, and 65 GPa–150 GPa for the P2_1/c-h-CaCO_3 structure, respectively. By fitting the third-order Birch–Murnaghan equation of state（EOS）, the values of bulk modulus K_0 and pressure derivative K~＇_0 are 66.09 GPa and 4.64 for aragonite, 81.93 GPa and 4.49 for post-aragonite, and 56.55 GPa and 5.40 for P2_1/c-h-CaCO_3, respectively, which are in good agreement with previous experimental and theoretical data. Elastic constants, wave velocities, and wave velocity anisotropies of the three highpressure CaCO_3 phases are obtained. Post-aragonite exhibits 25.90%–32.10% V_P anisotropy and 74.34%–104.30% V_S splitting anisotropy, and P2_1/c-h-CaCO_3 shows 22.30%–25.40% V_Panisotropy and 42.81%–48.00% V_S splitting anisotropy in the calculated pressure range. Compared with major minerals of the lower mantle, CaCO_3 high pressure polymorphs have low isotropic wave velocity and high wave velocity anisotropies. These results are important for understanding the deep carbon cycle and seismic wave velocity structure in the lower mantle.展开更多
The effect of lanthanum(La) on nitrogen atom diffusion in ε-Fe3N phase produced during nitriding with and without rare earth addition were studied based on the density function theory of first principles and the quan...The effect of lanthanum(La) on nitrogen atom diffusion in ε-Fe3N phase produced during nitriding with and without rare earth addition were studied based on the density function theory of first principles and the quantum mechanics program CASTEP code of Material Studio software.Calculated results show that the presence of La in ε-Fe3N phase can lead to the shrinks of a and b axis and the elongation of c axis of ε-Fe3N crystal cell.The total energy and the stability of the crystal cell with La are lower and higher than that without La,respectively.Diffusion activation energy of nitrogen atom in ε-Fe3N phase with La is 1.01 eV smaller than that in ε-Fe3N phase without La.This is the main reason why rare earth elements diffusing into compound layer produced during nitriding can accelerate the nitriding process or shorten the nitriding duration.展开更多
文摘The electronic structure,including band structure,density of states （DOS）, and partial density of states of SrTi1-xSbxO3 with x = 0,0. 125,0.25,and 0.33 is calculated from the first principles of plane wave ultra-soft pseudo-potential technology based on density function theory. The calculated results reveal that due to the electron doping,the Fermi level moves into the conduction bands for SrTi1-xSbxO3 with x = 0. 125 and the system shows metallic behavior. In addition, the DOS moves towards low energy and the optical band gap is broadened. The wide band gap and the low density of the states in the conduction band result in the transparency of the films.
基金ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.10804001 and No.11074003）, the Scientific Research Foundation for the Returned Overseas Chinese Scholars, State Education Ministry, and the program for innovative research team in Anhui Normal University of China.
文摘We have investigated properties of the compound LuAlO3：Ce^3＋ associated with the Ce^3＋ 4f-5d transition by using the periodic density functional theory. A hybrid functional has been used for the 4f states and a constrained approach has been employed for the excited 5d state. It is found that the average distance between Ce^3＋ and the eight nearest-neighbor O atoms decrease by 0.05 A on going from 4f to 5d state. The calculated Stokes shift is in good agreement with experiment. Based on the optimized structure around Ce^3＋, the energy level scheme of the 5d states has been evaluated using the angular overlap model, in reasonable agreement with experiment.
基金Project supported by the State Key Development Program for Basic Research of China (Grant No 2006CB605102)
文摘A model system consisting of Ni[001]（100）/Ni3Al[001]（100） multi-layers are studied using the density functional theory in order to explore the elastic properties of single crystal Ni-based superalloys. Simulation results are consistent with the experimental observation that rafted Ni-base superalloys virtually possess a cubic symmetry. The convergence of the elastic properties with respect to the thickness of the multilayers are tested by a series of multilayers from 2γ′＋2γto 10γ′＋10γ atomic layers. The elastic properties are found to vary little with the increase of the multilayer＇s thickness. A Ni/Ni3Al multilayer with 10γ′＋10γ atomic layers （3.54 nm） can be used to simulate the mechanical properties of Ni-base model superalloys. Our calculated elastic constants, bulk modulus, orientation-dependent shear modulus and Young＇s modulus, as well as the Zener anisotropy factor are all compatible with the measured results of Ni-base model superalloys R1 and the advanced commercial superalloys TMS-26, CMSX-4 at a low temperature. The mechanical properties as a function of the γ′ phase volume fraction are calculated by varying the proportion of the γ and γ′ phase in the multilayers. Besides, the mechanical properties of two-phase Ni/Ni3Al multilayer can be well predicted by the Voigt-Reuss-Hill rule of mixtures.
基金Supported by the National Natural Science Foundation of China (Nos. 50862005,51062005,91022034 and 91022027)the Jiangxi Natural Science Foundation and Cooperative Project (Nos. 2008GZC000,2009JX02060,2010GQW0038 and [2008]212)+1 种基金Foundation of Jiangxi Educational Committee (GJJ11204)the Jiangxi Colleges and Universities "Advanced Ceramics" scientific and technological innovation team
文摘The structural,electronic and optical properties of KNbO 3 （KN）,NaNbO3（NN）and K05 Na0.5NbO3（KNN） in paraelectric cubic phase were calculated employing the plane-wave pseudopotential method based on density functional theory （DFT）.The calculated electronic structures of the three crystals show similar features in the valence bands and the lower conduction bands.However,the structures in higher conduction bands differ markedly due to the effect of Na and K atoms.The calculated optical properties reveal that the features of optical spectrum at low energy are dominated by the transitions from O2p valence bands to Nb 4d conduction bands and those at high energy are related to the transitions to K 4s4p and/or Na 3s3p states.Moreover,the optical constants of KNN are approximately the average of KN and NN at high energy.Therefore,the optical properties of KNN in high energy region can probably be altered by changing the ratio of Na/K.
基金supported by the National Natural Science Foundation of China(Grant Nos.41174071,41373060,41374096,and 41403099)the Seismic Fund of Institute of Earthquake Science,China Earthquake Administration(CEA)(Grant Nos.2012IES0408,2014IES0407,and 2016IES0101)
文摘Elastic properties of three high pressure polymorphs of CaCO_3 are investigated based on first principles calculations.The calculations are conducted at 0 GPa–40 GPa for aragonite, 40 GPa–65 GPa for post-aragonite, and 65 GPa–150 GPa for the P2_1/c-h-CaCO_3 structure, respectively. By fitting the third-order Birch–Murnaghan equation of state（EOS）, the values of bulk modulus K_0 and pressure derivative K~＇_0 are 66.09 GPa and 4.64 for aragonite, 81.93 GPa and 4.49 for post-aragonite, and 56.55 GPa and 5.40 for P2_1/c-h-CaCO_3, respectively, which are in good agreement with previous experimental and theoretical data. Elastic constants, wave velocities, and wave velocity anisotropies of the three highpressure CaCO_3 phases are obtained. Post-aragonite exhibits 25.90%–32.10% V_P anisotropy and 74.34%–104.30% V_S splitting anisotropy, and P2_1/c-h-CaCO_3 shows 22.30%–25.40% V_Panisotropy and 42.81%–48.00% V_S splitting anisotropy in the calculated pressure range. Compared with major minerals of the lower mantle, CaCO_3 high pressure polymorphs have low isotropic wave velocity and high wave velocity anisotropies. These results are important for understanding the deep carbon cycle and seismic wave velocity structure in the lower mantle.
基金The work is financially supported by the National Natural Science Foundation of China(No 50471019)the PhD Program Foundation of Ministry of Education of China ( No 20060213017)National Defence Key Laboratory Foundation ( No 9140C500404070C5007)
文摘The effect of lanthanum(La) on nitrogen atom diffusion in ε-Fe3N phase produced during nitriding with and without rare earth addition were studied based on the density function theory of first principles and the quantum mechanics program CASTEP code of Material Studio software.Calculated results show that the presence of La in ε-Fe3N phase can lead to the shrinks of a and b axis and the elongation of c axis of ε-Fe3N crystal cell.The total energy and the stability of the crystal cell with La are lower and higher than that without La,respectively.Diffusion activation energy of nitrogen atom in ε-Fe3N phase with La is 1.01 eV smaller than that in ε-Fe3N phase without La.This is the main reason why rare earth elements diffusing into compound layer produced during nitriding can accelerate the nitriding process or shorten the nitriding duration.
