This paper deals with the electronic structure and stability of a series of carbides Mo2-xCrxC based on the pseudopotential plane-waves approach of density functional theory and using the generalized gradient approxim...This paper deals with the electronic structure and stability of a series of carbides Mo2-xCrxC based on the pseudopotential plane-waves approach of density functional theory and using the generalized gradient approximation(GGA) for the exchange and correlation potential.The calculation results of formation energies demonstrate that the structure Mo2-xCrxC in range of 0≤x≤1.75 is stable under ambient conditions.The formation energies/stabilities of the structures Mo2-xCrxC increase /reduce with enhancing the content of Cr in the structure.Calculated density of state(DOS) show that an increase in the content of Cr dissolving in Mo2-xCrxC crystal cell can lead to the crystal cell volume slightly to shrinkage,TDOS to be elevated at the Fermi level and the peak value of DOS to decrease at the lower energy region from-13.78 to-10.16 eV.Mulliken population analysis explains that the Mo2-xCrxC phase possess the metallic,covalent and ionic bonds.展开更多
The structural, elastic and electronic properties of Cu-X compounds in the Cu-X(X =Al, Be, Mg, Sn, Zn and Zr) systems were predicted systematically by first-principles calculations. The ground state properties such as...The structural, elastic and electronic properties of Cu-X compounds in the Cu-X(X =Al, Be, Mg, Sn, Zn and Zr) systems were predicted systematically by first-principles calculations. The ground state properties such as lattice constant, bulk modulus(B)and it's pressure derivative(B') were predicted by fitting a four-parameter Birch–Murnaghan equation and the elastic constants(cij′s)are determined by an efficient strain-stress method. The calculated lattice parameters and cij′s of these binary compounds agree well with the available experimental data in the literature. In addition, elastic properties of polycrystalline aggregates including bulk modulus(B), shear modulus(G), elastic modulus(E), B/G(bulk/shear) ratio, and anisotropy ratio(AU) are calculated and compared with the experimental and theoretical results available in the literature. Based on electronic density of states(DOS) analysis, it can be revealed that all the compounds in the present work are metallic in nature.展开更多
First-principles calculations were used to study the energetics and electronic structures of Ni and Sc co-doped MgH<sub>2</sub> system. The preferential positions for dopants were determined by the minimal...First-principles calculations were used to study the energetics and electronic structures of Ni and Sc co-doped MgH<sub>2</sub> system. The preferential positions for dopants were determined by the minimal total electronic energy. The results of formation enthalpy indicate that Ni and Sc co-doped MgH<sub>2</sub> system is more stable than Ni single-doped system. The hydrogen desorption enthalpies of these two hydrides are investigated. Ni and Sc co-doping can improve the dehydrogenation properties of MgH<sub>2</sub>. The lowest hydrogen desorption enthalpy of 0.30 eV appears in co-doped system, which is significantly lower than that of Ni doping. The electronic structure analysis illustrates that the hybridization of dopants with Mg and H atom together weakens the Mg-H interaction. And the Mg-H bonds are more susceptible to dissociate by Ni and Sc co-doping because of the reduced magnitude of Mg-H hybridization peaks. These behaviors effectively improve the dehydrogenation properties of Ni and Sc co-doped cases.展开更多
First-principles have been calculated to investigate the phase stabilities of the intermetallic phase of MgAl2 compounds by electronic structures and the charge distribution maps. The first-prin- ciples employed the n...First-principles have been calculated to investigate the phase stabilities of the intermetallic phase of MgAl2 compounds by electronic structures and the charge distribution maps. The first-prin- ciples employed the norm-conserving pseudo potential density functional method. They were calcu- lated both with the Ceperley and Alder data as parameterized by Perdew and Zunger(CA-PZ) of local-density approximation (LDA) and with the Perdew Burke Eruzerh (PBE) form of gradient-corrected approximation (GGA). A better method was found by comparing results from these two ultrasoft pseudo potentials. The present calculations indicate that LDA is better than GGA compared with references. This work also compared the lattice parameters, cohesive energy, formation enthalpy and electronic structure between theoretical results and experimental measurements (where available ). The calculations indicate that the unit cell volume get smaller after optimized and cohesive energy and formation enthalpy of C14 structure is the highest. The calculated structures are stable and the stability is aligned as C36 〈 C15 〈 C14.展开更多
Abstract" Ab initio density functional theory (DFT) was employed to study geometric and electronic structure of MgF2 (110) surface. Three different clean surface models have been considered. The results show that...Abstract" Ab initio density functional theory (DFT) was employed to study geometric and electronic structure of MgF2 (110) surface. Three different clean surface models have been considered. The results show that the surface terminated with one-layer F has the smallest relaxation and the lowest surface energy, which indicates this model is the most energetically favorable structure of MgF2(110) surface. Furthermore, the electronic properties are also discussed from the point of density of states and charge density. Analysis of electronic structure shows that the band gap of the surface is significantly narrowed with respect to the bulk. The electrons of the surface exhibit strong locality and larger effective mass.展开更多
We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon-clathrate compound(Na8Si46) under pressure using first-principles methods. The obtained dependencies of ...We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon-clathrate compound(Na8Si46) under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na8Si46 is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus,Young's modulus, Debye temperature,sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na8Si46 indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na8Si46.展开更多
By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice i...By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice is verified through phononmode analysis and room temperature molecular dynamics simulations. The carbon star lattice is found to be metallic due to the large states across the Fermi-level contributed by Pz orbital. Furthermore, the nanoribbons are also found to be metallic and no spin polarization occurs, except for the narrowest nanoribbon with one C12 ring, which has a ferromagnetic ground state. Our results show that carbon star lattice monolayer and nanoribbons have rich electronic properties with great potential in future electronic nanodevices.展开更多
The M-doping (M = Zr, Hf) effects on the electronic structures and thermoelectric performance of TiCoSb were studied by first-principles calculations. The band structure analysis shows that substituting Ti with M does...The M-doping (M = Zr, Hf) effects on the electronic structures and thermoelectric performance of TiCoSb were studied by first-principles calculations. The band structure analysis shows that substituting Ti with M does not change the band structures of these systems significantly. Most of the M-doped systems have a lower band gap value than that of TiCoSb;especially Ti0.5Zr0.5CoSb has the lowest energy band gap value of 0.971 eV. Besides, the amplitudes of the density of states in the region of the valence bands for M-doped systems show a similar but slightly higher value than TiCoSb. Those suggest that these compounds could have better thermoelectric performance than TiCoSb. The phonon dispersion relations show that the larger mass of Zr/Hf with respect to Ti lowers the optical modes and induces mixing with the acoustic branches. Our calculations offer a valuable insight on how to characterize complicated crystal structures of thermoelectric materials and optimize the material composition.展开更多
The energetic, electronic structure and elastic property of β-type Ti1-xXx (X=Nb and Mo, x=0.041 7, 0.062 5, 0.125 0, 0.187 5, 0.250 0, 0.312 5 and 0.375) binary alloys were calculated by the method of supercell and ...The energetic, electronic structure and elastic property of β-type Ti1-xXx (X=Nb and Mo, x=0.041 7, 0.062 5, 0.125 0, 0.187 5, 0.250 0, 0.312 5 and 0.375) binary alloys were calculated by the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. The elastic moduli of the polycrystals for these Ti1-xXx alloys were calculated from the elastic constants of the single crystal by the Voigt-Reuss-Hill averaging method. Based on the calculated results, the influence of X content on the phase stability and elastic property of β-type Ti1-xXx alloys was investigated. The results show that the phase stability, tetragonal shear constant C′, bulk modulus, elastic modulus and shear modulus of β-type Ti1-xXx alloys increase with an increase of X content monotonously. When the valence electron number of β-type Ti1-xXx alloys is around 4.10, i.e. the content of Nb is 9.87% (molar fraction) in the Ti-Nb alloy and Mo is 4.77% (molar fraction) in Ti-Mo alloy, the tetragonal shear constant is nearly zero. The Ti1-xXx alloys achieve low phase stability and low elastic modulus when the tetragonal shear constant reaches nearly zero. In addition, the phase stability of β-type Ti1-xXx alloys was discussed together with the calculated electronic structure.展开更多
The site occupancies and thermoelectric properties of tin-based clathrates Cs8M4Sn44□2 (M = Zn, Cd, Hg) and CssSn44□2 were studied by the first principle calculations. We had provided an efficient way to probe the...The site occupancies and thermoelectric properties of tin-based clathrates Cs8M4Sn44□2 (M = Zn, Cd, Hg) and CssSn44□2 were studied by the first principle calculations. We had provided an efficient way to probe the relationship between the crystalline structure and power factor. Detailed analyses indicated the p states of Sn at 16i and 24k sites together with the p states of M substitute contributed significantly to the maximum power factor, yet Cs atoms nearly did not. The dangling bonds of vacancies in Cs8Snn44□2 are also discussed. The power factors of p- and n-type CssMaSn42 and Cs8Sn44□2 at optimal temperature and carder concentration are predicted. Our results suggest that Cs8ZnaSn44□2 is a promising candidate at the 5.25 ×10^19 cm-3 hole carrier concentration as a high temperature thermoelectric material that is competitive to the state-of-art Ge-based clathrate thermoelectric materials.展开更多
The energetic and electronic structures of precipitates on the Cu-rich side of Cu-Ni-Si alloys were investigated by using the first-principle calculations based on plane-wave pseudopotential method.The negative format...The energetic and electronic structures of precipitates on the Cu-rich side of Cu-Ni-Si alloys were investigated by using the first-principle calculations based on plane-wave pseudopotential method.The negative formation heats and the cohesive energies of these precipitates were estimated with electronic structure calculations, and their structural stability was also analyzed.The results show thatδ-Ni2Si,γ-Ni5Si2 andβ-Ni3Si precipitates all have great alloying ability and structural stability,which,after comparing their density of states (DOS),is found attributed to the pseudogap effect near the Fermi level(Ef)and strong hybridization between the Ni-3d and Si-3p states.Compared with the other two precipitates,theδ-Ni2Si precipitate has the greatest structural stability,which is resulted from its lower DOS at Ef and the main bonding peaks slightly moving to the low energy region.展开更多
通过密度泛函理论(DFT)计算预测了三种具有五元环特征构型的二维硼化物结构,即penta-B_(4)X_(2)(X=S,Se,Te)。计算结果表明,三种penta-B_(4)X_(2)结构均表现出了良好的热力学、动力学、热学和力学稳定性。从结构上来看,penta-B_(4)X_(2...通过密度泛函理论(DFT)计算预测了三种具有五元环特征构型的二维硼化物结构,即penta-B_(4)X_(2)(X=S,Se,Te)。计算结果表明,三种penta-B_(4)X_(2)结构均表现出了良好的热力学、动力学、热学和力学稳定性。从结构上来看,penta-B_(4)X_(2)结构中的B—X共价键以及B—B共价键的共存有助于五边形框架的结构稳定性。此外,三种单层结构都具有较高的面内杨氏模量(最低为90.67 Nm^(-1)),其中二维penta-B_(4)Se_(2)单层在特定面内角方向上具有负泊松比(NPR)。电子能带结构表明所有单层结构都具有适中带隙(1.04、1.17、1.28 e V)的半导体材料。三种二维pentaB_(4)X_(2)对于不同波段的光波均具有较强的吸收系数,可见光区最高可达3.5×10~5 cm^(-1)的数量级,紫外光区域则表现出更强的光吸收能力。优异的光吸收性能使得二维penta-B_(4)X_(2)结构成为潜在的光致水解材料。展开更多
文摘This paper deals with the electronic structure and stability of a series of carbides Mo2-xCrxC based on the pseudopotential plane-waves approach of density functional theory and using the generalized gradient approximation(GGA) for the exchange and correlation potential.The calculation results of formation energies demonstrate that the structure Mo2-xCrxC in range of 0≤x≤1.75 is stable under ambient conditions.The formation energies/stabilities of the structures Mo2-xCrxC increase /reduce with enhancing the content of Cr in the structure.Calculated density of state(DOS) show that an increase in the content of Cr dissolving in Mo2-xCrxC crystal cell can lead to the crystal cell volume slightly to shrinkage,TDOS to be elevated at the Fermi level and the peak value of DOS to decrease at the lower energy region from-13.78 to-10.16 eV.Mulliken population analysis explains that the Mo2-xCrxC phase possess the metallic,covalent and ionic bonds.
基金Project(51021063)supported by Creative Research Group of National Natural Science Foundation of ChinaProject(2011CB610401)supported by National Basic Research Program of ChinaProject(2014M552150)supported by Postdoctoral Science Foundation of China
文摘The structural, elastic and electronic properties of Cu-X compounds in the Cu-X(X =Al, Be, Mg, Sn, Zn and Zr) systems were predicted systematically by first-principles calculations. The ground state properties such as lattice constant, bulk modulus(B)and it's pressure derivative(B') were predicted by fitting a four-parameter Birch–Murnaghan equation and the elastic constants(cij′s)are determined by an efficient strain-stress method. The calculated lattice parameters and cij′s of these binary compounds agree well with the available experimental data in the literature. In addition, elastic properties of polycrystalline aggregates including bulk modulus(B), shear modulus(G), elastic modulus(E), B/G(bulk/shear) ratio, and anisotropy ratio(AU) are calculated and compared with the experimental and theoretical results available in the literature. Based on electronic density of states(DOS) analysis, it can be revealed that all the compounds in the present work are metallic in nature.
文摘First-principles calculations were used to study the energetics and electronic structures of Ni and Sc co-doped MgH<sub>2</sub> system. The preferential positions for dopants were determined by the minimal total electronic energy. The results of formation enthalpy indicate that Ni and Sc co-doped MgH<sub>2</sub> system is more stable than Ni single-doped system. The hydrogen desorption enthalpies of these two hydrides are investigated. Ni and Sc co-doping can improve the dehydrogenation properties of MgH<sub>2</sub>. The lowest hydrogen desorption enthalpy of 0.30 eV appears in co-doped system, which is significantly lower than that of Ni doping. The electronic structure analysis illustrates that the hybridization of dopants with Mg and H atom together weakens the Mg-H interaction. And the Mg-H bonds are more susceptible to dissociate by Ni and Sc co-doping because of the reduced magnitude of Mg-H hybridization peaks. These behaviors effectively improve the dehydrogenation properties of Ni and Sc co-doped cases.
基金Supported by the Natural Science Foundation of China(50874054)the Natural Science Joint Foundation of China(u0837601)the Natural Science Foundation of Yunnan Province of China(2009CD134)
文摘First-principles have been calculated to investigate the phase stabilities of the intermetallic phase of MgAl2 compounds by electronic structures and the charge distribution maps. The first-prin- ciples employed the norm-conserving pseudo potential density functional method. They were calcu- lated both with the Ceperley and Alder data as parameterized by Perdew and Zunger(CA-PZ) of local-density approximation (LDA) and with the Perdew Burke Eruzerh (PBE) form of gradient-corrected approximation (GGA). A better method was found by comparing results from these two ultrasoft pseudo potentials. The present calculations indicate that LDA is better than GGA compared with references. This work also compared the lattice parameters, cohesive energy, formation enthalpy and electronic structure between theoretical results and experimental measurements (where available ). The calculations indicate that the unit cell volume get smaller after optimized and cohesive energy and formation enthalpy of C14 structure is the highest. The calculated structures are stable and the stability is aligned as C36 〈 C15 〈 C14.
基金Founded by the National Natural Science Foundation of China (Nos.5087407, 960976018, 51002102)Youth Foundation of Taiyuan University of Technology (No.2012L037)
文摘Abstract" Ab initio density functional theory (DFT) was employed to study geometric and electronic structure of MgF2 (110) surface. Three different clean surface models have been considered. The results show that the surface terminated with one-layer F has the smallest relaxation and the lowest surface energy, which indicates this model is the most energetically favorable structure of MgF2(110) surface. Furthermore, the electronic properties are also discussed from the point of density of states and charge density. Analysis of electronic structure shows that the band gap of the surface is significantly narrowed with respect to the bulk. The electrons of the surface exhibit strong locality and larger effective mass.
基金Project supported by National Natural Science Foundation of China(Grant Nos.11347134 and 11304254)the Doctor Foundation of Southwest University of Science and Technology,China(Grant No.13zx7125)
文摘We calculated the structural, elastic, and electronic properties of alkali metal Na atoms doped type-I silicon-clathrate compound(Na8Si46) under pressure using first-principles methods. The obtained dependencies of bond lengths and bond angles on pressure show heterogeneous behaviors which may bring out a structural transition. By using the elastic stability criteria from the calculated elastic constants, we confirm that the Na8Si46 is elastically unstable under high pressure. Some of the mechanical and thermal quantities include bulk modulus, shear modulus,Young's modulus, Debye temperature,sound velocity, melting point, and hardness, which are also derived from the elastic constants. The calculated total and partial electron densities of states of Na8Si46 indicate a weak interaction between the encapsulated Na atoms and the silicon framework. Moreover, the effect of pressure on its electronic structure is also investigated, which suggests that pressure is not a good choice to enhance the thermoelectricity performance of Na8Si46.
基金supported by the National Natural Science Foundation of China(Grant No.11274356)the Ministry of Environmental Protection of China(Grant Nos.200909086 and 201109037)
文摘By means of the first-principles calculations, we have investigated the structural stability and electronic properties of carbon star lattice monolayer and nanoribbons. The phase stability of the carbon star lattice is verified through phononmode analysis and room temperature molecular dynamics simulations. The carbon star lattice is found to be metallic due to the large states across the Fermi-level contributed by Pz orbital. Furthermore, the nanoribbons are also found to be metallic and no spin polarization occurs, except for the narrowest nanoribbon with one C12 ring, which has a ferromagnetic ground state. Our results show that carbon star lattice monolayer and nanoribbons have rich electronic properties with great potential in future electronic nanodevices.
文摘The M-doping (M = Zr, Hf) effects on the electronic structures and thermoelectric performance of TiCoSb were studied by first-principles calculations. The band structure analysis shows that substituting Ti with M does not change the band structures of these systems significantly. Most of the M-doped systems have a lower band gap value than that of TiCoSb;especially Ti0.5Zr0.5CoSb has the lowest energy band gap value of 0.971 eV. Besides, the amplitudes of the density of states in the region of the valence bands for M-doped systems show a similar but slightly higher value than TiCoSb. Those suggest that these compounds could have better thermoelectric performance than TiCoSb. The phonon dispersion relations show that the larger mass of Zr/Hf with respect to Ti lowers the optical modes and induces mixing with the acoustic branches. Our calculations offer a valuable insight on how to characterize complicated crystal structures of thermoelectric materials and optimize the material composition.
基金Project(50571063) supported by the National Natural Science Foundation of ChinaProject(04JC14054) supported by the Science and Technology Committee of Shanghai, China
文摘The energetic, electronic structure and elastic property of β-type Ti1-xXx (X=Nb and Mo, x=0.041 7, 0.062 5, 0.125 0, 0.187 5, 0.250 0, 0.312 5 and 0.375) binary alloys were calculated by the method of supercell and augmented plane waves plus local orbitals within generalized gradient approximation. The elastic moduli of the polycrystals for these Ti1-xXx alloys were calculated from the elastic constants of the single crystal by the Voigt-Reuss-Hill averaging method. Based on the calculated results, the influence of X content on the phase stability and elastic property of β-type Ti1-xXx alloys was investigated. The results show that the phase stability, tetragonal shear constant C′, bulk modulus, elastic modulus and shear modulus of β-type Ti1-xXx alloys increase with an increase of X content monotonously. When the valence electron number of β-type Ti1-xXx alloys is around 4.10, i.e. the content of Nb is 9.87% (molar fraction) in the Ti-Nb alloy and Mo is 4.77% (molar fraction) in Ti-Mo alloy, the tetragonal shear constant is nearly zero. The Ti1-xXx alloys achieve low phase stability and low elastic modulus when the tetragonal shear constant reaches nearly zero. In addition, the phase stability of β-type Ti1-xXx alloys was discussed together with the calculated electronic structure.
基金Supported by the 973 program(No.2010CB933501)NNSFC(Nos.20973175,21233009,and 21103190)
文摘The site occupancies and thermoelectric properties of tin-based clathrates Cs8M4Sn44□2 (M = Zn, Cd, Hg) and CssSn44□2 were studied by the first principle calculations. We had provided an efficient way to probe the relationship between the crystalline structure and power factor. Detailed analyses indicated the p states of Sn at 16i and 24k sites together with the p states of M substitute contributed significantly to the maximum power factor, yet Cs atoms nearly did not. The dangling bonds of vacancies in Cs8Snn44□2 are also discussed. The power factors of p- and n-type CssMaSn42 and Cs8Sn44□2 at optimal temperature and carder concentration are predicted. Our results suggest that Cs8ZnaSn44□2 is a promising candidate at the 5.25 ×10^19 cm-3 hole carrier concentration as a high temperature thermoelectric material that is competitive to the state-of-art Ge-based clathrate thermoelectric materials.
基金the National Natural Science Foundation of China(No.50571035)the National High Technology Research and Development Project(863) of China(No.2006AA032528)
文摘The energetic and electronic structures of precipitates on the Cu-rich side of Cu-Ni-Si alloys were investigated by using the first-principle calculations based on plane-wave pseudopotential method.The negative formation heats and the cohesive energies of these precipitates were estimated with electronic structure calculations, and their structural stability was also analyzed.The results show thatδ-Ni2Si,γ-Ni5Si2 andβ-Ni3Si precipitates all have great alloying ability and structural stability,which,after comparing their density of states (DOS),is found attributed to the pseudogap effect near the Fermi level(Ef)and strong hybridization between the Ni-3d and Si-3p states.Compared with the other two precipitates,theδ-Ni2Si precipitate has the greatest structural stability,which is resulted from its lower DOS at Ef and the main bonding peaks slightly moving to the low energy region.
文摘通过密度泛函理论(DFT)计算预测了三种具有五元环特征构型的二维硼化物结构,即penta-B_(4)X_(2)(X=S,Se,Te)。计算结果表明,三种penta-B_(4)X_(2)结构均表现出了良好的热力学、动力学、热学和力学稳定性。从结构上来看,penta-B_(4)X_(2)结构中的B—X共价键以及B—B共价键的共存有助于五边形框架的结构稳定性。此外,三种单层结构都具有较高的面内杨氏模量(最低为90.67 Nm^(-1)),其中二维penta-B_(4)Se_(2)单层在特定面内角方向上具有负泊松比(NPR)。电子能带结构表明所有单层结构都具有适中带隙(1.04、1.17、1.28 e V)的半导体材料。三种二维pentaB_(4)X_(2)对于不同波段的光波均具有较强的吸收系数,可见光区最高可达3.5×10~5 cm^(-1)的数量级,紫外光区域则表现出更强的光吸收能力。优异的光吸收性能使得二维penta-B_(4)X_(2)结构成为潜在的光致水解材料。