The(continuous) finite element approximations of different orders for the computation of the solution to electronic structures were proposed in some papers and the performance of these approaches is becoming appreciab...The(continuous) finite element approximations of different orders for the computation of the solution to electronic structures were proposed in some papers and the performance of these approaches is becoming appreciable and is now well understood.In this publication,the author proposes to extend this discretization for full-potential electronic structure calculations by combining the refinement of the finite element mesh,where the solution is most singular with the increase of the degree of the polynomial approximations in the regions where the solution is mostly regular.This combination of increase of approximation properties,done in an a priori or a posteriori manner,is well-known to generally produce an optimal exponential type convergence rate with respect to the number of degrees of freedom even when the solution is singular.The analysis performed here sustains this property in the case of Hartree-Fock and Kohn-Sham problems.展开更多
The finite element method is a promising method for electronic structure calculations.In this paper,a new parallelmesh refinementmethod for electronic structure calculations is presented.Some properties of the method ...The finite element method is a promising method for electronic structure calculations.In this paper,a new parallelmesh refinementmethod for electronic structure calculations is presented.Some properties of the method are investigated to make itmore efficient andmore convenient for implementation.Several practical issues such as distributed memory parallel computation,less tetrahedra prototypes,and the assignment of the mesh elements carried out independently in each sub-domain will be discussed.The numerical experiments on the periodic system,cluster and nano-tube are presented to demonstrate the effectiveness of the proposed method.展开更多
The electronic structure and spectra of [Mo3O4-nSn]^(4+)(n=0-4) cations were calculated by means of INDO/CI quantum chemistry method to account for the experimental data of their spectra in water solutions.
We report a study of the electronic structure and optical properties of uranium dioxide （U02） based on the ab-initio density-functional theory and using the generalized gradient approximation. To correctly describe ...We report a study of the electronic structure and optical properties of uranium dioxide （U02） based on the ab-initio density-functional theory and using the generalized gradient approximation. To correctly describe the strong correlation between 5 f electrons of a uranium atom, we employ the on-site Hubbard U correction term and optimize the correlation parameter of the bulk uranium dioxide. Then we give the structural and electronic properties of the ground state of uranium dioxide. Based on the accurate electronic structure, we calculate the complex dielectric function of UO2 and the related optieM properties, such as reflectivity, refractive index, extinction index, energy loss spectra, and absorption coefficient.展开更多
Single crystal of Ba2SbGaSs has been synthesized by the high temperature solidstate reaction method. The compound crystallizes in the orthorhombic space group Pnma with a = 12.177（4）, b = 8.880（3）, c = 8.982（3） ...Single crystal of Ba2SbGaSs has been synthesized by the high temperature solidstate reaction method. The compound crystallizes in the orthorhombic space group Pnma with a = 12.177（4）, b = 8.880（3）, c = 8.982（3） A, V= 971.4（6） A3, Z = 4, De = 4.284 g/cm3,μ = 14.487 mm-1, F（000） - 1096, the final R = 0.0171 and wR = 0.0384 for all data. The structure comprises an infinite one-dimensional 1∞[SbGaS5]4- anionic chain constructed from the GaS4 tetrahedra and the SbS5 polyhedra via sharing edge alternately. The paralleled 1∞[SbGaS5]4anionic chains engage with each other and form the two-dimensional Sb-Ga-S layer perpendicular to a-axis with the isolated Ba2＋ cations arranged between layers. The IR spectrum and the UV-Vis spectrum have been investigated. Also, the first-principles band structure and density of states calculations indicate that the compound belongs to indirect semiconductor with the band gap of 2.1 eV, which is supported by the UV-Vis diffuse reflectance results.展开更多
We investigate the electronic structures of one and two monolayer iron phthalocyanine （FePc） molecules on Au（111） surfaces. The first monolayer FePc is lying flat on the Au（111） substrate, and the second monolay...We investigate the electronic structures of one and two monolayer iron phthalocyanine （FePc） molecules on Au（111） surfaces. The first monolayer FePc is lying flat on the Au（111） substrate, and the second monolayer FePc is tilted at -15° relative to the substrate plane along the nearest neighbour [101] direction with a lobe downward to the central hole of the unit cell in the first layer. The structural information obtained by first-principles calculations is in agreement with the experiment results. Furthermore, it is demonstrated that the electronic structures of FePc molecules in one-monolayer FePc/Au（111） system are perturbed significantly, while the electronic structures of FePc molecules in the second monolayer in two-monolayer FePc/Au（111） system remain almost unchanged due to the screening of the buffer layer on Au（111）.展开更多
The zincblende ternary alloys Tl_xGa_（1-x） As（0 〈 x 〈 1） are studied by numerical analysis based on the plane wave pseudopotential method within the density functional theory and the local density approximation....The zincblende ternary alloys Tl_xGa_（1-x） As（0 〈 x 〈 1） are studied by numerical analysis based on the plane wave pseudopotential method within the density functional theory and the local density approximation. To model the alloys,16-atom supercells with the 2 × 2 × 2 dimensions are used and the dependency of the lattice parameter, bulk modulus,electronic structure, energy band gap, and optical bowing on the concentration x are analyzed. The results indicate that the ternary Tl_xGa_（1-x） As alloys have an average band gap bowing parameter of 4.48 eV for semiconductor alloys and 2.412 eV for semimetals. It is found that the band gap bowing strongly depends on composition and alloying a small Tl content with GaAs produces important modifications in the band structures of the alloys.展开更多
A new zero-dimensional（0D） thioborate Ba_9B_3GaS_（15） has been discovered by conventional high-temperature solid-state reaction. The compound crystallizes in orthorhombic space group Pbca with a = 8.4759（8）,b = ...A new zero-dimensional（0D） thioborate Ba_9B_3GaS_（15） has been discovered by conventional high-temperature solid-state reaction. The compound crystallizes in orthorhombic space group Pbca with a = 8.4759（8）,b = 22.266（2）,c = 31.426（3） ？,V = 5931（2） ？~3,Z = 8,Mr = 1819.11,Dc = 4.075 g/cm3,μ = 13.684 mm^（-1）,F（000） = 6320,S = 1.034,（Δρ）max = 5.039,（Δρ）min = –5.409 e/？~3,the final R = 0.0362 and w R = 0.1053 for 19243 observed reflections with I 〉 2σ（I）. The structure is constructed by discrete [BS_3]^（3–） trigonal planes and isolated [GaS_4]^（5–） tetrahedra with Ba^（2＋） and isolated S^（2–） filled among them. The UV-Vis-near-IR spectrum reveals a wide band gap of 3.15 eV that agrees with the electronic structure calculation.展开更多
The structural, electronic, elastic and magnetic properties of cerium, praseodymium and their hydrides REH x（RE=Ce, Pr and x=2, 3） were investigated by the first principles calculations based on density functional t...The structural, electronic, elastic and magnetic properties of cerium, praseodymium and their hydrides REH x（RE=Ce, Pr and x=2, 3） were investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At zero pressure all the hydrides were stable in the ferromagnetic state. The calculated lattice parameters were in good agreement with the experimental results. The bulk modulus decreased with the increase in the hydrogen content for these hydrides. The electronic structure revealed that di-hydrides were metallic whereas trihydrides were half metallic at zero pressure. A pressure-induced structural phase transition from cubic to hexagonal phase was predicted in these hydrides. The computed elastic constants indicated that these hydrides were mechanically stable at zero pressure. The calculated Debye temperature values were in good agreement with experimental and other theoretical results. A half metallic to metallic transition was also observed in REH3 under high pressure. Ferromagnetism was quenched in these hydrides at high pressures.展开更多
Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of rubidium metal hydrides RbMH4（M = B, Al, Ga） for five different crystal structures, nam...Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of rubidium metal hydrides RbMH4（M = B, Al, Ga） for five different crystal structures, namely hexagonal（P63mc）, tetragonal（P42/nmc）, tetragonal（P421c）, orthorhombic（Pnma） and monoclinic（P21/c）. Among the considered structures, tetragonal（P421c） phase is found to be the most stable one for these metal hydrides at normal pressure. A pressure-induced structural phase transition from tetragonal（P421c） to monoclinic（P21/c） phase is observed in all the three metal hydrides. The electronic structure reveals that these hydrides are wide band gap semiconductors. The calculated elastic constants indicate that these alkali metal tetrahydrides are mechanically stable at normal pressure.展开更多
We exploited a hydrogen-passivated germanium atomic cluster（Ge10H16） as a model to study the mechanism of lithium alloying with germanium. Based on the density functional theory, the electronic and crystal structure...We exploited a hydrogen-passivated germanium atomic cluster（Ge10H16） as a model to study the mechanism of lithium alloying with germanium. Based on the density functional theory, the electronic and crystal structures of lithium-alloyed Ge10H16 were investigated. The theoretical results indicate that the alloying of lithium with Ge10H16 will weaken the germanium-hydrogen bond and repel the closest germanium atom away from the alloyed lithium atom. Based on the maps of the electron density distribution, the nature of the lithium-germanium chemical bond was analyzed. Moreover, the diffusion process of the lithium on the Ge10H16 cluster was detected, which suggested that there is a close relationship between the diffusion barriers and the coordination number around the lithium atom.展开更多
Kinetic investigations including quasi-classical trajectory and canonical unified statistical theory method calculations are carried out on a potential energy surface for the hydrogen-abstraction reaction from methane...Kinetic investigations including quasi-classical trajectory and canonical unified statistical theory method calculations are carried out on a potential energy surface for the hydrogen-abstraction reaction from methane by atom O(^3P).The surface is constructed using a modified Shepard interpolation method.The ab initio calculations are performed at the CCSD(T)level.Taking account of the contribution of inner core electrons to electronic correlation interaction in ab initio electronic structure calculations,modified optimized aug-cc-pCVQZ basis sets are applied to the all-electrons calculations.On this potential energy surface,the triplet oxygen atom attacks methane in a near-collinear H-CH3 direction to form a saddle point with barrier height of 13.55 kcal/mol,which plays a key role in the kinetics of the title reaction.For the temperature range of 298-2500 K,our calculated thermal rate constants for the O(^3P)+CH4→OH+CH3 reaction show good agreement with relevant experimental data.This work provides detailed mechanism of this gas-phase reaction and a theoretical guidance for methane combustion.展开更多
We present the local density approximate＋Gutzwiller results for the electronic structure of Cal-xSrxVOa. The substitution of Sr2＋ by Ca2＋ reduces the bandwidth, as the V-O-V bond angle decreases from 180° for ...We present the local density approximate＋Gutzwiller results for the electronic structure of Cal-xSrxVOa. The substitution of Sr2＋ by Ca2＋ reduces the bandwidth, as the V-O-V bond angle decreases from 180° for SrVO3 to about 160° for CaVO3. However, we find that the bandwidth decrease induced by the V-O-V bond angle decrease is smaller as compared to that induced by electron correlation. In correlated electron systems, such as Cal-=Sr=VOa, the correlation effect of 3d electrons plays a leading role in determining the bandwidth. The electron correlation effect and crystal field splitting collaboratively determine whether the compounds will be in a metal state or in a Mort-insulator phase.展开更多
We conduct a systematic investigation of the role of Hubbard U corrections in electronic structure calculations of two-dimensional(2D)materials containing 3d transition metals.Specifically,we use density functional th...We conduct a systematic investigation of the role of Hubbard U corrections in electronic structure calculations of two-dimensional(2D)materials containing 3d transition metals.Specifically,we use density functional theory(DFT)with the PBE and PBE+U approximations to calculate the crystal structure,band gaps,and magnetic parameters of 638 monolayers.Based on a comprehensive comparison to experiments we first establish that the inclusion of the U correction worsens the accuracy for the lattice constants.Consequently,PBE structures are used for subsequent property evaluations.The band gaps show a significant dependence on U.In particular,for 134(21%)of the materials the U parameter induces a metal-to-insulator transition.For the magnetic materials we calculate the magnetic moment,magnetic exchange coupling,and magnetic anisotropy parameters.In contrast to the band gaps,the size of the magnetic moments shows only weak dependence on U.Both the exchange energies and magnetic anisotropy parameters are systematically reduced by theU correction.On this basis we conclude that the Hubbard U correction will lead to lower predicted Curie temperatures in 2D materials.All the calculated properties are available in the Computational 2D Materials Database(C2DB).展开更多
Based on first-principles calculations, the electronic and magnetic properties of undoped and Li-doped rutile TiO2 have been studied. The results demonstrate that a cation vacancy can arouse ferromagnetism in TiO2 and...Based on first-principles calculations, the electronic and magnetic properties of undoped and Li-doped rutile TiO2 have been studied. The results demonstrate that a cation vacancy can arouse ferromagnetism in TiO2 and the magnetic moment mainly comes from p orbitals of O atoms around the Ti vacancy. However, the Ti vacancy under normal conditions is very difficult to form due to its high formation energy. Our calculations indicate that Li-doped TiO2 can reduce the formation energy while keeping the magnetism. The large magnetization energy indicates that Li-doped TiO2 is a promising room-temperature diluted magnetic semiconductor.展开更多
First principles calculations are carried out to investigate the structural stability of several non-equilibrium intermetallic phases in the cobalt（Co）–Mo system using spin polarized projected augmented-wave potent...First principles calculations are carried out to investigate the structural stability of several non-equilibrium intermetallic phases in the cobalt（Co）–Mo system using spin polarized projected augmented-wave potentials. It is revealed that the Co3Mo, CoMo, and CoMo3 alloys are energetically favored to be in D019, B11, and A15 structures, respectively,and that the magnetic moments of Co atoms would decrease rapidly with an increasing percentage of Mo content and would most probably disappear when the content of Mo is no less than 50 at%. Generally, the calculated results in the present work match well with the available experimental observations.展开更多
Electronic structure calculations in the time domain provide a deeper understanding of nonequilibrium dynamics in materials.The real-time Boltzmann equation(rt-BTE),used in conjunction with accurate interactions compu...Electronic structure calculations in the time domain provide a deeper understanding of nonequilibrium dynamics in materials.The real-time Boltzmann equation(rt-BTE),used in conjunction with accurate interactions computed from first principles,has enabled reliable predictions of coupled electron and lattice dynamics.However,the timescales and system sizes accessible with this approach are still limited,with two main challenges being the different timescales of electron and phonon interactions and the cost of computing collision integrals.As a result,only a few examples of these calculations exist,mainly for two-dimensional(2D)materials.Here we leverage adaptive and multirate time integration methods to achieve a major step forward in solving the coupled rt-BTEs for electrons and phonons.Relative to conventional(non-adaptive)time-stepping,our approach achieves a 10x speedup for a target accuracy,or greater accuracy by 3–6 orders of magnitude for the same computational cost,enabling efficient calculations in both 2D and bulk materials.This efficiency is showcased by computing the coupled electron and lattice dynamics in graphene up to~100 ps,as well as modeling ultrafast lattice dynamics and thermal diffuse scattering maps in bulk materials(silicon and gallium arsenide).In addition to improved efficiency,our adaptive method can resolve the characteristic rates of different physical processes,thus naturally bridging different timescales.This enables simulations of longer timescales and provides a framework for modeling multiscale dynamics of coupled degrees of freedomin matter.Our work opens new opportunities for quantitative studies of nonequilibrium physics in materials,including driven lattice dynamics with phonons coupled to electrons,spin,and other degrees of freedom.展开更多
Calculating the impact of point defects on the macroscopic properties of technologically relevantsemiconductors remains a considerable challenge. Semi-empirical approaches, such as the tightbindingmethod, are very eff...Calculating the impact of point defects on the macroscopic properties of technologically relevantsemiconductors remains a considerable challenge. Semi-empirical approaches, such as the tightbindingmethod, are very efficient in calculating the electronic structure of large supercells containingone or several defects. However, the accuracy of these calculations depends on the quality of theparameters. Obtaining reliable parameters by fitting to the large number of entangled bands indefective supercells is a demanding task.We therefore present an alternative way by fitting to the atomand orbital projected densities of states. Starting with a tight-binding fit of the pristine material,we onlyneed a few physically motivated parameters for the fitting of defects. The training is done on data setsgenerated purely with parameter variations of tight-binding Hamiltonians. We demonstrate theefficiency of our approach for the calculation of the carbon monomer and the carbon dimersubstitutions in hexagonal boron nitride. The method opens a path towards understandingcomplicated defect landscapes using a computationally affordable semi-empirical approach withoutsacrificing accuracy.展开更多
We develop a generalization of Nesterov’s accelerated gradient descent method which is designed to deal with orthogonality constraints.To demonstrate the effectiveness of our method,we perform numerical experiments w...We develop a generalization of Nesterov’s accelerated gradient descent method which is designed to deal with orthogonality constraints.To demonstrate the effectiveness of our method,we perform numerical experiments which demonstrate that the number of iterations scales with the square root of the condition number,and also compare with existing state-of-the-art quasi-Newton methods on the Stiefel manifold.Our experiments show that our method outperforms existing state-of-the-art quasi-Newton methods on some large,ill-conditioned problems.展开更多
Ionization and dissociation of nitrosyl chloride CINO were studied using femtosecond laser mass spectra technique. Strong fragmental ions NO^＋ and Cl^＋ were observed with the laser intensity varied from 3.2× 10...Ionization and dissociation of nitrosyl chloride CINO were studied using femtosecond laser mass spectra technique. Strong fragmental ions NO^＋ and Cl^＋ were observed with the laser intensity varied from 3.2× 10^14 to 2.5×10^15 W/cm^2. These fragmental ions were attributed to the direct dissociation of the parent ions. Electronic structure calculations were also carried out with Hartree-Fock, density functional and correlated levels of theory to understand the possible fragmentation pathways. The very low N-Cl bond energy in the parent ion of nitrosyl chloride is a clear reason for the absence of CINO^＋ and CIN^＋ ion peaks from the femtosecond laser mass spectrum.展开更多
文摘The(continuous) finite element approximations of different orders for the computation of the solution to electronic structures were proposed in some papers and the performance of these approaches is becoming appreciable and is now well understood.In this publication,the author proposes to extend this discretization for full-potential electronic structure calculations by combining the refinement of the finite element mesh,where the solution is most singular with the increase of the degree of the polynomial approximations in the regions where the solution is mostly regular.This combination of increase of approximation properties,done in an a priori or a posteriori manner,is well-known to generally produce an optimal exponential type convergence rate with respect to the number of degrees of freedom even when the solution is singular.The analysis performed here sustains this property in the case of Hartree-Fock and Kohn-Sham problems.
基金This work is partially supported by NSF of China,the National Basic Research Program of China,MOE and Shanghai basic research project.
文摘The finite element method is a promising method for electronic structure calculations.In this paper,a new parallelmesh refinementmethod for electronic structure calculations is presented.Some properties of the method are investigated to make itmore efficient andmore convenient for implementation.Several practical issues such as distributed memory parallel computation,less tetrahedra prototypes,and the assignment of the mesh elements carried out independently in each sub-domain will be discussed.The numerical experiments on the periodic system,cluster and nano-tube are presented to demonstrate the effectiveness of the proposed method.
文摘The electronic structure and spectra of [Mo3O4-nSn]^(4+)(n=0-4) cations were calculated by means of INDO/CI quantum chemistry method to account for the experimental data of their spectra in water solutions.
基金Supported by the New Century Excellent Talents in University in Ministry of Education of China under Grant No NCET-09-0867
文摘We report a study of the electronic structure and optical properties of uranium dioxide （U02） based on the ab-initio density-functional theory and using the generalized gradient approximation. To correctly describe the strong correlation between 5 f electrons of a uranium atom, we employ the on-site Hubbard U correction term and optimize the correlation parameter of the bulk uranium dioxide. Then we give the structural and electronic properties of the ground state of uranium dioxide. Based on the accurate electronic structure, we calculate the complex dielectric function of UO2 and the related optieM properties, such as reflectivity, refractive index, extinction index, energy loss spectra, and absorption coefficient.
文摘Single crystal of Ba2SbGaSs has been synthesized by the high temperature solidstate reaction method. The compound crystallizes in the orthorhombic space group Pnma with a = 12.177（4）, b = 8.880（3）, c = 8.982（3） A, V= 971.4（6） A3, Z = 4, De = 4.284 g/cm3,μ = 14.487 mm-1, F（000） - 1096, the final R = 0.0171 and wR = 0.0384 for all data. The structure comprises an infinite one-dimensional 1∞[SbGaS5]4- anionic chain constructed from the GaS4 tetrahedra and the SbS5 polyhedra via sharing edge alternately. The paralleled 1∞[SbGaS5]4anionic chains engage with each other and form the two-dimensional Sb-Ga-S layer perpendicular to a-axis with the isolated Ba2＋ cations arranged between layers. The IR spectrum and the UV-Vis spectrum have been investigated. Also, the first-principles band structure and density of states calculations indicate that the compound belongs to indirect semiconductor with the band gap of 2.1 eV, which is supported by the UV-Vis diffuse reflectance results.
基金supported by the National Natural Science Foundation of China (Grant No.10774176)the National Basic Research Program of China (Grant Nos.2006CB806202 and 2006CB921305)the Shanghai Supercomputing Center,Chinese Academy of Sciences
文摘We investigate the electronic structures of one and two monolayer iron phthalocyanine （FePc） molecules on Au（111） surfaces. The first monolayer FePc is lying flat on the Au（111） substrate, and the second monolayer FePc is tilted at -15° relative to the substrate plane along the nearest neighbour [101] direction with a lobe downward to the central hole of the unit cell in the first layer. The structural information obtained by first-principles calculations is in agreement with the experiment results. Furthermore, it is demonstrated that the electronic structures of FePc molecules in one-monolayer FePc/Au（111） system are perturbed significantly, while the electronic structures of FePc molecules in the second monolayer in two-monolayer FePc/Au（111） system remain almost unchanged due to the screening of the buffer layer on Au（111）.
文摘The zincblende ternary alloys Tl_xGa_（1-x） As（0 〈 x 〈 1） are studied by numerical analysis based on the plane wave pseudopotential method within the density functional theory and the local density approximation. To model the alloys,16-atom supercells with the 2 × 2 × 2 dimensions are used and the dependency of the lattice parameter, bulk modulus,electronic structure, energy band gap, and optical bowing on the concentration x are analyzed. The results indicate that the ternary Tl_xGa_（1-x） As alloys have an average band gap bowing parameter of 4.48 eV for semiconductor alloys and 2.412 eV for semimetals. It is found that the band gap bowing strongly depends on composition and alloying a small Tl content with GaAs produces important modifications in the band structures of the alloys.
基金Supported by the National Natural Science Foundation of China(21233009,21225104,91422303,21301175 and 21171168)
文摘A new zero-dimensional（0D） thioborate Ba_9B_3GaS_（15） has been discovered by conventional high-temperature solid-state reaction. The compound crystallizes in orthorhombic space group Pbca with a = 8.4759（8）,b = 22.266（2）,c = 31.426（3） ？,V = 5931（2） ？~3,Z = 8,Mr = 1819.11,Dc = 4.075 g/cm3,μ = 13.684 mm^（-1）,F（000） = 6320,S = 1.034,（Δρ）max = 5.039,（Δρ）min = –5.409 e/？~3,the final R = 0.0362 and w R = 0.1053 for 19243 observed reflections with I 〉 2σ（I）. The structure is constructed by discrete [BS_3]^（3–） trigonal planes and isolated [GaS_4]^（5–） tetrahedra with Ba^（2＋） and isolated S^（2–） filled among them. The UV-Vis-near-IR spectrum reveals a wide band gap of 3.15 eV that agrees with the electronic structure calculation.
文摘The structural, electronic, elastic and magnetic properties of cerium, praseodymium and their hydrides REH x（RE=Ce, Pr and x=2, 3） were investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At zero pressure all the hydrides were stable in the ferromagnetic state. The calculated lattice parameters were in good agreement with the experimental results. The bulk modulus decreased with the increase in the hydrogen content for these hydrides. The electronic structure revealed that di-hydrides were metallic whereas trihydrides were half metallic at zero pressure. A pressure-induced structural phase transition from cubic to hexagonal phase was predicted in these hydrides. The computed elastic constants indicated that these hydrides were mechanically stable at zero pressure. The calculated Debye temperature values were in good agreement with experimental and other theoretical results. A half metallic to metallic transition was also observed in REH3 under high pressure. Ferromagnetism was quenched in these hydrides at high pressures.
文摘Ab initio calculations are performed to investigate the structural stability, electronic structure and mechanical properties of rubidium metal hydrides RbMH4（M = B, Al, Ga） for five different crystal structures, namely hexagonal（P63mc）, tetragonal（P42/nmc）, tetragonal（P421c）, orthorhombic（Pnma） and monoclinic（P21/c）. Among the considered structures, tetragonal（P421c） phase is found to be the most stable one for these metal hydrides at normal pressure. A pressure-induced structural phase transition from tetragonal（P421c） to monoclinic（P21/c） phase is observed in all the three metal hydrides. The electronic structure reveals that these hydrides are wide band gap semiconductors. The calculated elastic constants indicate that these alkali metal tetrahydrides are mechanically stable at normal pressure.
基金financially supported by the Projects of Undergraduate Innovation&entrepreneurship Training Plans of Quanzhou Normal University(No.201310399008)Quanzhou‘‘Tong-Jiang Scholar"program,Fujian‘‘MinJiang Scholar"program,program for New Century Excellent Talents in University(No.NCET-13-0879)the Education and Scientific Research Foundation(Class A)for Young Teachers of Education Bureau of Fujian Province,China(No.JA13263)
文摘We exploited a hydrogen-passivated germanium atomic cluster（Ge10H16） as a model to study the mechanism of lithium alloying with germanium. Based on the density functional theory, the electronic and crystal structures of lithium-alloyed Ge10H16 were investigated. The theoretical results indicate that the alloying of lithium with Ge10H16 will weaken the germanium-hydrogen bond and repel the closest germanium atom away from the alloyed lithium atom. Based on the maps of the electron density distribution, the nature of the lithium-germanium chemical bond was analyzed. Moreover, the diffusion process of the lithium on the Ge10H16 cluster was detected, which suggested that there is a close relationship between the diffusion barriers and the coordination number around the lithium atom.
基金Project supported by the National Natural Science Foundation of China(Grant No.51574016)and completed while the author was in residence at UNSW,Australia supported by the International Cooperation Training Program for Innovative Talents of USTB.
文摘Kinetic investigations including quasi-classical trajectory and canonical unified statistical theory method calculations are carried out on a potential energy surface for the hydrogen-abstraction reaction from methane by atom O(^3P).The surface is constructed using a modified Shepard interpolation method.The ab initio calculations are performed at the CCSD(T)level.Taking account of the contribution of inner core electrons to electronic correlation interaction in ab initio electronic structure calculations,modified optimized aug-cc-pCVQZ basis sets are applied to the all-electrons calculations.On this potential energy surface,the triplet oxygen atom attacks methane in a near-collinear H-CH3 direction to form a saddle point with barrier height of 13.55 kcal/mol,which plays a key role in the kinetics of the title reaction.For the temperature range of 298-2500 K,our calculated thermal rate constants for the O(^3P)+CH4→OH+CH3 reaction show good agreement with relevant experimental data.This work provides detailed mechanism of this gas-phase reaction and a theoretical guidance for methane combustion.
基金Project supported by the National Natural Science Foundation of China (Grant No.10947001)
文摘We present the local density approximate＋Gutzwiller results for the electronic structure of Cal-xSrxVOa. The substitution of Sr2＋ by Ca2＋ reduces the bandwidth, as the V-O-V bond angle decreases from 180° for SrVO3 to about 160° for CaVO3. However, we find that the bandwidth decrease induced by the V-O-V bond angle decrease is smaller as compared to that induced by electron correlation. In correlated electron systems, such as Cal-=Sr=VOa, the correlation effect of 3d electrons plays a leading role in determining the bandwidth. The electron correlation effect and crystal field splitting collaboratively determine whether the compounds will be in a metal state or in a Mort-insulator phase.
基金the European Research Council(ERC)under the European Union’s Horizon 2020 research and innovation programme Grant No.773122(LIMA)and Grant agreement No.951786(NOMAD CoE)A high-performance computing infrastructure for data-driven research on sustainable energy materials,Grant no.NNF22OC0078009.K.S.T.is a Villum Investigator supported by VILLUM FONDEN(grant no.37789).
文摘We conduct a systematic investigation of the role of Hubbard U corrections in electronic structure calculations of two-dimensional(2D)materials containing 3d transition metals.Specifically,we use density functional theory(DFT)with the PBE and PBE+U approximations to calculate the crystal structure,band gaps,and magnetic parameters of 638 monolayers.Based on a comprehensive comparison to experiments we first establish that the inclusion of the U correction worsens the accuracy for the lattice constants.Consequently,PBE structures are used for subsequent property evaluations.The band gaps show a significant dependence on U.In particular,for 134(21%)of the materials the U parameter induces a metal-to-insulator transition.For the magnetic materials we calculate the magnetic moment,magnetic exchange coupling,and magnetic anisotropy parameters.In contrast to the band gaps,the size of the magnetic moments shows only weak dependence on U.Both the exchange energies and magnetic anisotropy parameters are systematically reduced by theU correction.On this basis we conclude that the Hubbard U correction will lead to lower predicted Curie temperatures in 2D materials.All the calculated properties are available in the Computational 2D Materials Database(C2DB).
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11005049 and 61006051)
文摘Based on first-principles calculations, the electronic and magnetic properties of undoped and Li-doped rutile TiO2 have been studied. The results demonstrate that a cation vacancy can arouse ferromagnetism in TiO2 and the magnetic moment mainly comes from p orbitals of O atoms around the Ti vacancy. However, the Ti vacancy under normal conditions is very difficult to form due to its high formation energy. Our calculations indicate that Li-doped TiO2 can reduce the formation energy while keeping the magnetism. The large magnetization energy indicates that Li-doped TiO2 is a promising room-temperature diluted magnetic semiconductor.
基金financially supported by the National Natural Science Foundation of China (Nos. 50971072 and 51131003)the National Basic Research Program of China (Nos. 2011CB606301 and 2012CB825700)the administration of Key Laboratory of Advanced Materials in Tsinghua University
文摘First principles calculations are carried out to investigate the structural stability of several non-equilibrium intermetallic phases in the cobalt（Co）–Mo system using spin polarized projected augmented-wave potentials. It is revealed that the Co3Mo, CoMo, and CoMo3 alloys are energetically favored to be in D019, B11, and A15 structures, respectively,and that the magnetic moments of Co atoms would decrease rapidly with an increasing percentage of Mo content and would most probably disappear when the content of Mo is no less than 50 at%. Generally, the calculated results in the present work match well with the available experimental observations.
基金supported by the U.S.Department of Energy,Office of Science,under the Office of Advanced Scientific Computing Research and Office of Basic Energy Sciences,through the Scientific Discovery through Advanced Computing(SciDAC)program,including support from the Frameworks,Algorithms and Software Technologies for Mathematics(FASTMath)Institute,the Next-Generation Scientific Software Technologies Program,and the SciDAC Partnership“Traversing the death valley between short and long times in non-equilibrium quantum dynamics”under the Award Numbers DE-SC0022088(Caltech)DE-AC52-07NA27344(LLNL)+2 种基金J.Y.,I.M.and M.B.acknowledge additional support by the Liquid Sunlight Alliance,which is supported by the U.S.Department of Energy,Office of Science,Office of Basic Energy Sciences,Fuels from Sunlight Hub under Award Number DE-SC0021266For the development of the interface between PERTURBO and SUNDIALS,J.Y.and M.B.were supported by the National Science Foundation under Grant No.OAC-2209262.This work was performed in part under the auspices of the U.S.Department of Energy by Lawrence Livermore National Laboratory under contract DE-AC52-07NA27344.LLNL-JRNL-2001089This research used resources of the National Energy Research Scientific Computing Center(NERSC),a U.S.Department of Energy Office of Science User Facility located at Lawrence Berkeley National Laboratory,operated under Contract No.DE-AC02-05CH11231.
文摘Electronic structure calculations in the time domain provide a deeper understanding of nonequilibrium dynamics in materials.The real-time Boltzmann equation(rt-BTE),used in conjunction with accurate interactions computed from first principles,has enabled reliable predictions of coupled electron and lattice dynamics.However,the timescales and system sizes accessible with this approach are still limited,with two main challenges being the different timescales of electron and phonon interactions and the cost of computing collision integrals.As a result,only a few examples of these calculations exist,mainly for two-dimensional(2D)materials.Here we leverage adaptive and multirate time integration methods to achieve a major step forward in solving the coupled rt-BTEs for electrons and phonons.Relative to conventional(non-adaptive)time-stepping,our approach achieves a 10x speedup for a target accuracy,or greater accuracy by 3–6 orders of magnitude for the same computational cost,enabling efficient calculations in both 2D and bulk materials.This efficiency is showcased by computing the coupled electron and lattice dynamics in graphene up to~100 ps,as well as modeling ultrafast lattice dynamics and thermal diffuse scattering maps in bulk materials(silicon and gallium arsenide).In addition to improved efficiency,our adaptive method can resolve the characteristic rates of different physical processes,thus naturally bridging different timescales.This enables simulations of longer timescales and provides a framework for modeling multiscale dynamics of coupled degrees of freedomin matter.Our work opens new opportunities for quantitative studies of nonequilibrium physics in materials,including driven lattice dynamics with phonons coupled to electrons,spin,and other degrees of freedom.
基金funded by the Luxembourg National Research Fund(FNR),grant reference PRIDE17/12246511/PACEin part by the Austrian Science Fund(FWF)10.55776/COE5.We would like to acknowledge Christoph Schattauer and Mohamed Ali Abdulmalik for fruitful discussions.
文摘Calculating the impact of point defects on the macroscopic properties of technologically relevantsemiconductors remains a considerable challenge. Semi-empirical approaches, such as the tightbindingmethod, are very efficient in calculating the electronic structure of large supercells containingone or several defects. However, the accuracy of these calculations depends on the quality of theparameters. Obtaining reliable parameters by fitting to the large number of entangled bands indefective supercells is a demanding task.We therefore present an alternative way by fitting to the atomand orbital projected densities of states. Starting with a tight-binding fit of the pristine material,we onlyneed a few physically motivated parameters for the fitting of defects. The training is done on data setsgenerated purely with parameter variations of tight-binding Hamiltonians. We demonstrate theefficiency of our approach for the calculation of the carbon monomer and the carbon dimersubstitutions in hexagonal boron nitride. The method opens a path towards understandingcomplicated defect landscapes using a computationally affordable semi-empirical approach withoutsacrificing accuracy.
文摘We develop a generalization of Nesterov’s accelerated gradient descent method which is designed to deal with orthogonality constraints.To demonstrate the effectiveness of our method,we perform numerical experiments which demonstrate that the number of iterations scales with the square root of the condition number,and also compare with existing state-of-the-art quasi-Newton methods on the Stiefel manifold.Our experiments show that our method outperforms existing state-of-the-art quasi-Newton methods on some large,ill-conditioned problems.
基金Project supported by the Hundred Talent Fund of Chinese Academy of Sciences and the National Natural Science Foundation of China （Nos. 20477047, 20473094）.
文摘Ionization and dissociation of nitrosyl chloride CINO were studied using femtosecond laser mass spectra technique. Strong fragmental ions NO^＋ and Cl^＋ were observed with the laser intensity varied from 3.2× 10^14 to 2.5×10^15 W/cm^2. These fragmental ions were attributed to the direct dissociation of the parent ions. Electronic structure calculations were also carried out with Hartree-Fock, density functional and correlated levels of theory to understand the possible fragmentation pathways. The very low N-Cl bond energy in the parent ion of nitrosyl chloride is a clear reason for the absence of CINO^＋ and CIN^＋ ion peaks from the femtosecond laser mass spectrum.
