The effects of Fe–C/N co-doping on the electronic and optical properties of NaTaO_3 are studied with density functional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermod...The effects of Fe–C/N co-doping on the electronic and optical properties of NaTaO_3 are studied with density functional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermodynamically stable.The co-doping sodium tantalate can reduce the energy band gap to a greater degree due to the synergistic effects of Fe and C(N) atoms than mono-doping sodium tantalate, and has a larger optical absorption of the whole visible spectrum. The band alignments for the doped NaTaO_3 are well positioned for the feasibility of hydrogen production by water splitting. The Fe–C co-doping can enhance the absorption of the visible light and its photocatalytic activity more than Fe–N co-doping due to the different locations of impurity energy levels originating from their p–d hybridization effect.展开更多
Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy(V)migration energies of SmxCe1-xO2-δ(x=0.0625,0.125,0.25 andδ=0.0625,0.125)systems using a GGA+U method are studied.Calculated re...Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy(V)migration energies of SmxCe1-xO2-δ(x=0.0625,0.125,0.25 andδ=0.0625,0.125)systems using a GGA+U method are studied.Calculated results show that advantage migration types change from V→O2-to O2-→as x andδincrease.For V→O2-migrations of the Sm0.0625Ce0.9375O1.9375 and Sm0.125Ce0.875O1.9375 systems,electrostatic attractions between Sm"and V,defect associations between Ce3 and V,and steric hindrances of Sm3+affect the migration energies.For O2→V migrations of the Sm0.125Ce0.875O1.875 and Sm0.25Ce0.75O1.875 systems,migration energies of O2-are affected by electrostatic repulsions between Sm3+and O2-and defect associations between Ce3+and V.Increases of the oxygen vacancy and Sm3+doping concentrations benefit the oxygen ion and vacancy migrations,respectively.展开更多
Hybrid density functional theory is employed to systematically investigate the structural,magnetic,vibrational,thermodynamic properties of plutonium monocarbide(Pu C and Pu C_(0.75)).For comparison,the results obtaine...Hybrid density functional theory is employed to systematically investigate the structural,magnetic,vibrational,thermodynamic properties of plutonium monocarbide(Pu C and Pu C_(0.75)).For comparison,the results obtained by DFT,DFT + U are also given.For Pu C and Pu C_(0.75),Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic(AFM) structure.The calculated phonon spectra suggest that Pu C and Pu C_(0.75) are dynamically stable.Values of the Helmholtz free energy ?F,internal energy ?E,entropy S,and constant-volume specific heat C_v of Pu C and Pu C_(0.75) are given.The results are in good agreement with available experimental or theoretical data.As for the chemical bonding nature,the difference charge densities,the partial densities of states and the Bader charge analysis suggest that the Pu–C bonds of Pu C and Pu C_(0.75) have a mixture of covalent character and ionic character.The effect of carbon vacancy on the chemical bonding is also discussed in detail.We expect that our study can provide some useful reference for further experimental research on the phonon density of states,thermodynamic properties of the plutonium monocarbide.展开更多
First-principles calculations based on density functional theory corrected by Hubbard parameter U(DFT+U) are applied to the study on the co-adsorption of O2 and H_2O molecules to α-U(110) surface. The calculation res...First-principles calculations based on density functional theory corrected by Hubbard parameter U(DFT+U) are applied to the study on the co-adsorption of O2 and H_2O molecules to α-U(110) surface. The calculation results show that DFT+U method with Ueff= 1.5 e V can yield the experimental results of lattice constant and elastic modulus of α-uranium bulk well. Of all 7 low index surfaces of α-uranium, the(001) surface is the most stable with lowest surface energy while the(110) surface possesses the strongest activity with the highest surface energy. The adsorptions of O_2 and H_2O molecules are investigated separated. The O_2 dissociates spontaneously in all initial configurations. For the adsorption of H_2O molecule,both molecular and dissociative adsorptionsoccur. Through calculations of co-adsorption, it can be confirmed that the inhibition effect of O_2 on the corrosion of uranium by water vapor originates from the preferential adsorption mechanism,while the consumption of H atoms by O atoms exerted little influence on the corrosion of uranium.展开更多
The density functional calculation is performed for centrosymmetric(La–Pm) GaO_3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA+U exchange correlation to treat h...The density functional calculation is performed for centrosymmetric(La–Pm) GaO_3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA+U exchange correlation to treat highly correlated electrons due to the very localized 4f orbitals of rare earth elements, and explore the influence of U = 0.478 Ry on the magnetic phase stability and the densities of states. LSDA+U calculation shows that the ferromagnetic(FM) state of RGaO_3 is energetically more favorable than the anti-ferromagnetic(AFM) one, except for LaGaO_3 where the NM state is the lowest in energy. The energy band gaps of RGaO_3 are found to be in the range of 3.8–4.0 eV, indicating the semiconductor character with a large gap.展开更多
Cl-containing cerium dioxide(Ce O2) catalysts have been found to exhibit unique catalytic activities. In the present work, using density functional theory calculations with the inclusion of on-site Coulomb correction,...Cl-containing cerium dioxide(Ce O2) catalysts have been found to exhibit unique catalytic activities. In the present work, using density functional theory calculations with the inclusion of on-site Coulomb correction, we systematically studied the effect of Cl on the physicochemical properties of Ce O2 surfaces by substituting one subsurface O with Cl. The calculated results show that substituting an O atom with a Cl atom results in structural distortion and the reduction of one surface Ce4+ cation to Ce3+. The protruding Ce3+ cation greatly improves the adsorption energy of O2 to produce an active O2- species, and maintains the catalytic oxidation cycle of CO on Ce O2(110). These results may help us obtain a better understanding of Cl-ceria interacting systems and provide some guidance for the design of effective Ce O2-based catalysts.展开更多
We have studied the electronic,magnetic and optical properties of neodymium chalcogenides by performing LSDA+U and full potential linearized augmented plane wave(FP-LAPW) method.The electronic structure calculation sh...We have studied the electronic,magnetic and optical properties of neodymium chalcogenides by performing LSDA+U and full potential linearized augmented plane wave(FP-LAPW) method.The electronic structure calculation shows that the electronic states in Nd-chalcogenides were mainly contributed by Nd-4f electrons near Fermi energy and 3p,4p and 5p state electrons of X(S,Se and Te),respectively.We have also studied the absorption of light via the imaginary parts of the dielectric function of Nd-chalcogenides.展开更多
本文采用第一性原理的方法系统研究了UO2的晶体结构、电子结构和弹性性质.在计算中采用广义梯度近似结合Hubbard U项描述电子的局域强关联效应.首先通过计算能带带隙大小并与理论值比较的方法,得到了合理的有效库仑相关作用能(Ueff)的取...本文采用第一性原理的方法系统研究了UO2的晶体结构、电子结构和弹性性质.在计算中采用广义梯度近似结合Hubbard U项描述电子的局域强关联效应.首先通过计算能带带隙大小并与理论值比较的方法,得到了合理的有效库仑相关作用能(Ueff)的取值,同时通过态密度的计算,进一步验证了Ueff取值的合理性.计算得到UO2中U原子的Ueff值为3.30 e V(Ueff=U-J,U=3.70 e V,J=0.40 e V).应用此参数计算得到的UO2晶格常数为5.54,带隙宽度为2.17 e V.该结果优于目前现有的研究结果,同时在同样的Ueff值条件下计算所得到的弹性常数与实验值也符合得较好.相较于之前的基于实验测量并分析得到的Ueff值,我们所采用的方法在对UO2性质描述上更为准确.不同的有效库仑相关作用能取值下的态密度结果表明,有效库仑相关作用能的大小可以影响铀原子5f电子轨道的分布.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.51572219 and 11204239)the Project of the Natural Science Foundation of Shaanxi Province,China(Grant Nos.2015JM1018,2013JQ1018,and 15JK1714)+1 种基金the Project of Natural Science Foundation of Department of Education of Shaanxi Province,China(Grant No.15JK1759)the Science Foundation of Northwest University of China(Grant No.12NW06)
文摘The effects of Fe–C/N co-doping on the electronic and optical properties of NaTaO_3 are studied with density functional theory. Our calculations indicate that mono-doped and co-doped sodium tantalate are both thermodynamically stable.The co-doping sodium tantalate can reduce the energy band gap to a greater degree due to the synergistic effects of Fe and C(N) atoms than mono-doping sodium tantalate, and has a larger optical absorption of the whole visible spectrum. The band alignments for the doped NaTaO_3 are well positioned for the feasibility of hydrogen production by water splitting. The Fe–C co-doping can enhance the absorption of the visible light and its photocatalytic activity more than Fe–N co-doping due to the different locations of impurity energy levels originating from their p–d hybridization effect.
基金Supported by the National Natural Science Foundation of China(No.51474133)Inner Mongolia Natural Science Foundation(No.2016MS0513)
文摘Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy(V)migration energies of SmxCe1-xO2-δ(x=0.0625,0.125,0.25 andδ=0.0625,0.125)systems using a GGA+U method are studied.Calculated results show that advantage migration types change from V→O2-to O2-→as x andδincrease.For V→O2-migrations of the Sm0.0625Ce0.9375O1.9375 and Sm0.125Ce0.875O1.9375 systems,electrostatic attractions between Sm"and V,defect associations between Ce3 and V,and steric hindrances of Sm3+affect the migration energies.For O2→V migrations of the Sm0.125Ce0.875O1.875 and Sm0.25Ce0.75O1.875 systems,migration energies of O2-are affected by electrostatic repulsions between Sm3+and O2-and defect associations between Ce3+and V.Increases of the oxygen vacancy and Sm3+doping concentrations benefit the oxygen ion and vacancy migrations,respectively.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.21371160 and 21401173)
文摘Hybrid density functional theory is employed to systematically investigate the structural,magnetic,vibrational,thermodynamic properties of plutonium monocarbide(Pu C and Pu C_(0.75)).For comparison,the results obtained by DFT,DFT + U are also given.For Pu C and Pu C_(0.75),Fock-0.25 hybrid functional gives the best lattice constants and predicts the correct ground states of antiferromagnetic(AFM) structure.The calculated phonon spectra suggest that Pu C and Pu C_(0.75) are dynamically stable.Values of the Helmholtz free energy ?F,internal energy ?E,entropy S,and constant-volume specific heat C_v of Pu C and Pu C_(0.75) are given.The results are in good agreement with available experimental or theoretical data.As for the chemical bonding nature,the difference charge densities,the partial densities of states and the Bader charge analysis suggest that the Pu–C bonds of Pu C and Pu C_(0.75) have a mixture of covalent character and ionic character.The effect of carbon vacancy on the chemical bonding is also discussed in detail.We expect that our study can provide some useful reference for further experimental research on the phonon density of states,thermodynamic properties of the plutonium monocarbide.
基金Project supported by the National Nature Science Foundation of China(Grant Nos.51401237,11474358,and 51271198)
文摘First-principles calculations based on density functional theory corrected by Hubbard parameter U(DFT+U) are applied to the study on the co-adsorption of O2 and H_2O molecules to α-U(110) surface. The calculation results show that DFT+U method with Ueff= 1.5 e V can yield the experimental results of lattice constant and elastic modulus of α-uranium bulk well. Of all 7 low index surfaces of α-uranium, the(001) surface is the most stable with lowest surface energy while the(110) surface possesses the strongest activity with the highest surface energy. The adsorptions of O_2 and H_2O molecules are investigated separated. The O_2 dissociates spontaneously in all initial configurations. For the adsorption of H_2O molecule,both molecular and dissociative adsorptionsoccur. Through calculations of co-adsorption, it can be confirmed that the inhibition effect of O_2 on the corrosion of uranium by water vapor originates from the preferential adsorption mechanism,while the consumption of H atoms by O atoms exerted little influence on the corrosion of uranium.
文摘The density functional calculation is performed for centrosymmetric(La–Pm) GaO_3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA+U exchange correlation to treat highly correlated electrons due to the very localized 4f orbitals of rare earth elements, and explore the influence of U = 0.478 Ry on the magnetic phase stability and the densities of states. LSDA+U calculation shows that the ferromagnetic(FM) state of RGaO_3 is energetically more favorable than the anti-ferromagnetic(AFM) one, except for LaGaO_3 where the NM state is the lowest in energy. The energy band gaps of RGaO_3 are found to be in the range of 3.8–4.0 eV, indicating the semiconductor character with a large gap.
基金This work was supported by the National Natural Science Foundation of China （No.U1232118, No.21203099）, the National Basic Research Program （No.2014CB932403）, the Program of Introducing Talents of Disciplines to China Universities （No.B06006）, Research Program for Advanced and Applied Technology of Tianjin （No.13JCYBJC36800）, Doctoral Fund of Ministry of Education of China （No.20120031120033）, Fok Ying Tung Education Foundation （No.151008）, and Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund （the second phase）. We appreciate the supports from the National Super-Computing Center at Tianjin and Guangzhou.
基金supported by the National Natural Science Foundation of China (21431003)the National Program on Key Basic Research Project (2014CB932101)the Fundamental Research Funds for the Central Universities (buctrc201514)
基金supported by the National Basic Research Program of China(2011CB808505)the National Natural Science Foundation of China(21322307,21421004)+1 种基金the"Shu Guang"project of Shanghai Municipal Education CommissionShanghai Education Development Foundation(13SG30)for financial support
文摘Cl-containing cerium dioxide(Ce O2) catalysts have been found to exhibit unique catalytic activities. In the present work, using density functional theory calculations with the inclusion of on-site Coulomb correction, we systematically studied the effect of Cl on the physicochemical properties of Ce O2 surfaces by substituting one subsurface O with Cl. The calculated results show that substituting an O atom with a Cl atom results in structural distortion and the reduction of one surface Ce4+ cation to Ce3+. The protruding Ce3+ cation greatly improves the adsorption energy of O2 to produce an active O2- species, and maintains the catalytic oxidation cycle of CO on Ce O2(110). These results may help us obtain a better understanding of Cl-ceria interacting systems and provide some guidance for the design of effective Ce O2-based catalysts.
基金This work was supported by the National Natural Science Foundation of China （No. 11474004）, the National Science Foundation of Henan Province （No. 162300410001） and the Natural Science Foundation of Shaanxi University of Technology （No. SLGQD2017-13）.
文摘We have studied the electronic,magnetic and optical properties of neodymium chalcogenides by performing LSDA+U and full potential linearized augmented plane wave(FP-LAPW) method.The electronic structure calculation shows that the electronic states in Nd-chalcogenides were mainly contributed by Nd-4f electrons near Fermi energy and 3p,4p and 5p state electrons of X(S,Se and Te),respectively.We have also studied the absorption of light via the imaginary parts of the dielectric function of Nd-chalcogenides.
文摘本文采用第一性原理的方法系统研究了UO2的晶体结构、电子结构和弹性性质.在计算中采用广义梯度近似结合Hubbard U项描述电子的局域强关联效应.首先通过计算能带带隙大小并与理论值比较的方法,得到了合理的有效库仑相关作用能(Ueff)的取值,同时通过态密度的计算,进一步验证了Ueff取值的合理性.计算得到UO2中U原子的Ueff值为3.30 e V(Ueff=U-J,U=3.70 e V,J=0.40 e V).应用此参数计算得到的UO2晶格常数为5.54,带隙宽度为2.17 e V.该结果优于目前现有的研究结果,同时在同样的Ueff值条件下计算所得到的弹性常数与实验值也符合得较好.相较于之前的基于实验测量并分析得到的Ueff值,我们所采用的方法在对UO2性质描述上更为准确.不同的有效库仑相关作用能取值下的态密度结果表明,有效库仑相关作用能的大小可以影响铀原子5f电子轨道的分布.
