I had the privilege and the pleasure to work closely with Stephen J. Pennycook for about twenty years, having a group of post-docs and Vanderbilt-University graduate students embedded in his electron microscopy group ...I had the privilege and the pleasure to work closely with Stephen J. Pennycook for about twenty years, having a group of post-docs and Vanderbilt-University graduate students embedded in his electron microscopy group at Oak Ridge National Laboratory, spending on average a day per week there. We combined atomic-resolution imaging of materials,electron-energy-loss spectroscopy, and density-functional-theory calculations to explore and elucidate diverse materials phenomena, often resolving long-standing issues. This paper is a personal perspective of that journey, highlighting a few examples to illustrate the power of combining theory and microscopy and closing with an assessment of future prospects.展开更多
Effectively separating bastnaesite from calcium-bearing gangue minerals(particularly calcite)presents a formidable challenge,making the development of efficient collectors crucial.To achieve this,we have designed and ...Effectively separating bastnaesite from calcium-bearing gangue minerals(particularly calcite)presents a formidable challenge,making the development of efficient collectors crucial.To achieve this,we have designed and synthesized a novel,highly efficient,water-soluble cationic collector,N-dodecylisopropanolamine(NDIA),for use in the bastnaesite-calcite flotation process.Density functional theory(DFT)calculations identified the amine nitrogen atom in NDIA as the site most susceptible to electrophilic attack and electron loss.By introducing an OH group into the traditional collector dodecylamine(DDA)structure,NDIA provided additional adsorption sites,enabling synergistic adsorption on the surface of bastnaesite,thereby significantly enhancing both the floatability and selectivity of these minerals.The recovery of bastnaesite was 76.02%,while the calcite was 1.26%.The NDIA markedly affected the zeta potential of bastnaesite,while its impact on calcite was relatively minor.Detailed Fourier-transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)results elucidated that the―NH―and―OH groups in NDIA anchored onto the bastnaesite surface through robust electrostatic and hydrogen bonding interactions,thereby enhancing bastnaesite's affinity for NDIA.Furthermore,in situ atomic force microscopy(AFM)provided conclusive evidence of NDIA aggregation on the bastnaesite surface,improving contact angle and hydrophobicity,and significantly boosting the flotation recovery of bastnaesite.展开更多
Using high-throughput first-principles calculations, we systematically studied the synergistic effect of alloying two elements （AI and 28 kinds of 3d, 4d, and 5d transition metals） on the elastic constants and elast...Using high-throughput first-principles calculations, we systematically studied the synergistic effect of alloying two elements （AI and 28 kinds of 3d, 4d, and 5d transition metals） on the elastic constants and elastic moduli of γ-Ni. We used machine learning to theoretically predict the relationship between alloying concentration and mechanical properties, giving the binding energy between the two elements. We found that the ternary alloying elements strengthened the 7 phase in the order of Re 〉 Ir 〉 W 〉 Ru 〉 Cr 〉 Mo 〉 Pt 〉 Ta 〉 Co. There is a quadratic parabolic relationship between the number of d shell electrons in the alloying element and the bulk modulus, and the maximum bulk modulus appears when the d shell is half full. We found a linear relationship between bulk modulus and alloying concentration over a certain alloying range. Using linear regression, we found the linear fit concentration coefficient of 29 elements. Using machine learning to theoretically predict the bulk modulus and lattice constants of Ni32XY, we predicted values close to the calculated results, with a regression parameter of R2 = 0.99626. Compared with pure Ni, the alloyed Ni has higher bulk modulus B, G, E, Cll, and C44, but equal Cl2. The alloying strengthening in some of these systems is closely tied to the binding of elements, indicating that the binding energy of the alloy is a way to assess its elastic properties.展开更多
The paper presents analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV(particle image velocimetry)and pressure probe traverses.PIV measurements have alread...The paper presents analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV(particle image velocimetry)and pressure probe traverses.PIV measurements have already been performed at middle height inside one diffuser channel passage for a given speed of rotation and various mass flow rates.These results have been already presented in several previous communications.New experiments have been performed using a three-hole pressure probe traverses from hub to shroud diffuser width at different radial locations between the two diffuser geometrical throats.Numerical simulations are also realized with the commercial codes Star CCM+7.02.011 and CFX.Frozen rotor and fully unsteady calculations of the whole pump have been performed.Comparisons between numerical results,previous experimental PIV results and new probe traverses one's are presented and discussed for one mass flow rate.In this respect,a first attempt to take into account fluid leakages between the rotating and fixed part of the pump has been checked since it may affects the real flow structure inside the diffuser.展开更多
The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal struc...The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states （DOS） is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters （e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function） are calculated for the first time. The study of dielectric constant （ε1） indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values （DOS, Debye temperature, atomic mass, etc.） suggests that the compound is less likely to be superconductor.展开更多
Nuclear data are the cornerstones of reactor physics and shielding calculations.Recently,China released CENDL-3.2 in 2020,and the US released ENDF/B-VIII.0 in 2018.Therefore,it is necessary to comprehensively evaluate...Nuclear data are the cornerstones of reactor physics and shielding calculations.Recently,China released CENDL-3.2 in 2020,and the US released ENDF/B-VIII.0 in 2018.Therefore,it is necessary to comprehensively evaluate the criticality computing performance of these newly released evaluated nuclear libraries.In this study,we used the NJOY2016 code to generate ACE format libraries based on the latest neutron data libraries(including CENDL-3.2,JEFF3.3,ENDF/B-VIII.0,and JENDL4.0).The MCNP code was used to conduct a detailed analysis of fission nuclides,including^(235)U,^(233)U,and^(239)Pu,in different evaluated nuclear data libraries based on 100 benchmarks.The criticality calculation performance of each library was evaluated using three statistical parameters:δk/σ,χ^(2),and<|Δ|>.Analysis of theδk/σparameter showed that CENDL-3.1 and JENDL-4.0 both had>10 benchmarks that exceeded 3r,whereas CENDL3.2,ENDFB-VIII.0,and JEFF-3.3 had,7,5,and 4 benchmarks,respectively,exceeding 3r.The ENDF/B-VII.1 library performed best,with only two benchmarks exceeding 3r.Compared to CENDL-3.1,CENDL-3.2 offers an improvement in criticality calculations.Compared to the JEFF-3.3 and ENDF/B-VIII.0 libraries,CENDL3.2 performs better in the calculation of the^(233)U assemblies,but it performs poorly in the pusl11 series case calculation of the^(239)Pu assemblies,and thus further improvement is needed.展开更多
Mechanical, electronic, and thermodynamic properties of zirconium carbide have been systematically studied using the ab initio calculations. The calculated equilibrium lattice parameter, bulk modulus, and elastic cons...Mechanical, electronic, and thermodynamic properties of zirconium carbide have been systematically studied using the ab initio calculations. The calculated equilibrium lattice parameter, bulk modulus, and elastic constants are all well consistent with the experimental data. The electronic band structure indicates that the mixture of C 2p and Zr 4d and 4p orbitals around the Fermi level makes a large covalent contribution to the chemical bonds between the C and Zr atoms. The Bader charge analysis suggests that there are about 1.71 electrons transferred from each Zr atom to its nearest C atom. Therefore, the Zr-C bond displays a mixed ionic/covalent character. The calculated phonon dispersions of ZrC are stable, coinciding with the experimental measurement. A drastic expansion in the volume of ZrC is seen with increasing temperature, while the bulk modulus decreases linearly. Based on the calculated phonon dispersion curves and within the quasi-harmonic approximation, the temperature dependence of the heat capacities is obtained, which gives a good description compared with the available experimental data.展开更多
The geometry, electronic structure and magnetic property of the hexagonal AlN(h-AlN) sheet doped by 5d atoms(Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the den...The geometry, electronic structure and magnetic property of the hexagonal AlN(h-AlN) sheet doped by 5d atoms(Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C3v and D3h. The symmetry will deviate from exact C3v and D3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0μBfor Lu, Ta and Ir; 1μB for Hf, W, Pt and Hg; 2μB for Re and Au; and 3μB for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries.展开更多
Heterostructures(HSs)have attracted significant attention because of their interlayer van der Waals interactions.The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored...Heterostructures(HSs)have attracted significant attention because of their interlayer van der Waals interactions.The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored in this work using density functional theory.The results indicate that the direct band gap(1.95 e V)of the Ga N-MoS2 HS is lower than the individual band gaps of both the GaN layer(3.48 e V)and the MoS2 layer(2.03 eV)based on HSE06 hybrid functional calculations.Specifically,the GaN-MoS2 HS is a typical type-II band HS semiconductor that provides an effective approach to enhance the charge separation efficiency for improved photocatalytic degradation activity and water splitting efficiency.Under tensile or compressive strain,the direct band gap of the GaN-MoS2 HS undergoes redshifts.Additionally,the GaN-MoS2 HS maintains its direct band gap semiconductor behavior even when the tensile or compressive strain reaches 5%or-5%.Therefore,the results reported above can be used to expand the application of Ga N-MoS2 HSs to photovoltaic cells and photocatalysts.展开更多
We study the negative thermal expansion(NTE) properties and effect of Na insertion on the NTE of the framework material GaFe(CN)_6 by first-principles calculations based on density functional theory within the quasi-h...We study the negative thermal expansion(NTE) properties and effect of Na insertion on the NTE of the framework material GaFe(CN)_6 by first-principles calculations based on density functional theory within the quasi-harmonic approximation. The calculated results show that the material exhibits NTE due to the low transverse vibrational modes of the CN groups. The modes demonstrate larger negative values of the mode Grüneisen parameters. Once Na is introduced in the framework of the material, it prefers to locate at the center of the quadrates of the framework material and binds to the four N anions nearby. As a consequence, the transverse vibrational mode of the CN group is clearly hindered and the NTE of the material is weakened. Our theoretical calculations have clarified the mechanisms of NTE and the effect of the guest Na on the NTE of the framework material.展开更多
The elastic, magnetoelastic, and phonon properties of Ni2FeGa were investigated through first-principles calculations. The obtained elastic and phonon dispersion curves for the austenite and martensite phases agree we...The elastic, magnetoelastic, and phonon properties of Ni2FeGa were investigated through first-principles calculations. The obtained elastic and phonon dispersion curves for the austenite and martensite phases agree well with available the- oretical and experimental results. The isotropic elastic moduli are also predicted along with the polycrystalline aggregate properties including the bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio. The Pugh ratio indicates that Ni2FeGa shows ductility, especially the austenite phase, which is consistent with the experimental results. The Debye tem- peratures of the Ni2FeGa in the austenite and martensite phases are 344 K and 392 K, respectively. It is predicted that the magnetoelastic coefficient is -5.3 x 10^6 J/m3 and magnetostriction coefficient is between 135 and 55 ppm in the Ni2FeGa austenite phase.展开更多
The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory.Silicane ...The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory.Silicane is staler against the metal adatoms than silicene.Hydrogenation makes the adsorption energies of various metal atoms considered in our calculations on silicane significantly lower than those on silicene.Similar diffusion energy barriers of alkali metal atoms on silicane and silicene could be observed.However,the diffusion energy barriers of alkali-earth metal atoms on silicane are essentially lower than those on silicene due to the small structural distortion and weak interaction between metal atoms and silicane substrate.Combining the adsorption energy with the diffusion energy barriers,it is found that the clustering would occur when depositing metal atoms on perfect hydrogenated silicene with relative high coverage.In order to avoid forming a metal cluster,we need to remove the hydrogen atoms from the silicane substrate to achieve the defective silicane.Our results are helpful for understanding the interaction between metal atoms and silicene-based two-dimensional materials.展开更多
The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approach...The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approaches are used to explore effective methods to predict dielectric constants of a series of 12 energetic materials(EMs)for which experimental data needed to experimentally determine the dielectric constant(refractive indices)are available.These include military grades energetic materials,nitro and peroxide compounds,and the widely used nitroglycerin.Ab-initio and DFT calculations are conducted.In order to calculate dielectric constant values of materials,potential DFT functional combined with basis sets are considered for testing.Accuracy of the calculations are compared to experimental data listed in the scientific literature,and time required for calculations are both evaluated and discussed.The best functional/basis set combinations among those tested are CAM-B3LYP and AUG-ccpVDZm,which provide great results,with accuracy deviations below 5%when calculated results are compared to experimental data.展开更多
The recently discovered tetragonal, monoclinie and orthorhombic polymorphs of M3N4 （M=C, Si, Sn） are in- vestigated by using first-principles calculations. A set of anisotropic elastic quantities, i.e., the bulk and...The recently discovered tetragonal, monoclinie and orthorhombic polymorphs of M3N4 （M=C, Si, Sn） are in- vestigated by using first-principles calculations. A set of anisotropic elastic quantities, i.e., the bulk and shear moduli, Young＇s modulus, Poisson ratio, H/G ratio and rickets hardness of M3N4 （M=C, Si, Sn） are predicted. The quasi-harmonic Debye model, assuming that the solids are isotopic, may lead to large errors for the non-cubic crystals. The thermal effects are obtained by the traditional quasi-harmonic approach. The dependences of heat capacity, thermal expansion coefficient and Debye temperature on temperature and pressure are systematically discussed in the pressure range of 0 IOGPa and in the temperature range of 0-1100 K. More importantly, o- C3N4 is a negative thermal expansion material. Our results may have important consequences in shaping the understanding of the fundamental properties of these binary nitrides.展开更多
Several rocksalt Sr4X3N （X = O, S, Se, and Te） are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their ma...Several rocksalt Sr4X3N （X = O, S, Se, and Te） are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr4X3N possibly have higher Curie temperatures and have more stable half metallicity than the Sr4X3C. Their crystal-cell magnetic moments are all 1.00 μB. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp2 hybridized orbitals in the Sr4X3N. Then two Sr-5s and three N-2p electrons enter into three sp2 hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp2 hybridized orbitals.展开更多
We employed ab-initio calculations to investigate the structural and thermodynamic properties of Massicot or orthorhombic phase of PbO named β-PbO using the projector augmented-wave（PAW） method within the generaliz...We employed ab-initio calculations to investigate the structural and thermodynamic properties of Massicot or orthorhombic phase of PbO named β-PbO using the projector augmented-wave（PAW） method within the generalized gradient approximation（GGA）. The temperature and pressure dependence of bulk modulus, heat capacity at constant pressure and constant volume, entropy, thermal expansion coefficient and Grüneisen parameter were discussed. Accuracy of two different models, the Debye and Debye-Grüneisen which are based on the quasi-harmonic approximation（QHA） for producing thermodynamic properties of material were compared. According to calculation results, these two models can be used to designate thermodynamic properties for β-PbO with sensible accuracy over a wide range of temperatures and pressures, and our work on the properties of this structure will be useful for more deeply understanding various properties of this structure.展开更多
The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom prob...The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom probe tomography.The Re distribution of single,nearest neighbor(NN),next-nearest neighbor(NNN),and cluster configurations are respectively designed in the models withγandγphases.The results show that the Re atoms tend to enteringγphase and the Re atoms prefer to occupy the Al sites inγphase.The Re cluster with a combination of NN and NNN Re-Re pair configuration is not preferred than the isolated Re atom in the Ni-based superalloys,and the configuration with isolated Re atom is more preferred in the system.Especially,the electronic states are analyzed and the energetic parameters are calculated.The electronic structure analyses show there exists strong Ni-Re electronic interaction and it is mainly contributed by the d-d hybridization.The characteristic features of the electronic states of the Re doping effects are also given.It is also found that Re atoms prefer the Al sites inγside at the interface.The density of states at or near the Fermi level and the d-d hybridizations of NN Ni-Re are found to be important in the systems.展开更多
The mechanical properties of formamidinium halide perovskites FABX_3(FA=CH(NH_2)_2; B=Pb, Sn; X=Br, I)are systematically investigated using first-principles calculations. Our results reveal that FABX_3 perovskites pos...The mechanical properties of formamidinium halide perovskites FABX_3(FA=CH(NH_2)_2; B=Pb, Sn; X=Br, I)are systematically investigated using first-principles calculations. Our results reveal that FABX_3 perovskites possess excellent mechanical flexibility, ductility and strong anisotropy. We shows that the planar organic cation FA+ has an important effect on the mechanical properties of FABX3 perovskites. In addition, our results indicate that (i) the moduli(bulk modulus B, Young's modulus E, and shear modulus G) of FABBr_3 are larger than those of FABI_3 for the same B atom, and (ii) the moduli of FAPbX_3 are larger than those of FASnX_3 for the same halide atom. The reason for the two trends is demonstrated by carefully analyzing the bond strength between B and X atoms based on the projected crystal orbital Hamilton population method.展开更多
sing first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX（X = S, Se, Te） bulk and nanowires（NWs） under unia...sing first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX（X = S, Se, Te） bulk and nanowires（NWs） under uniaxial [0001] strain. Due to the intrinsic shrinking strain induced by surface contraction, large NWs with {10ˉ10} facets have heavy hole（HH）-like valence band maximum（VBM） states, while NWs with {11ˉ20} facets have crystal hole（CH）-like VBM states. The external uniaxial strain induces an HH–CH band crossing at a critical strain for both bulk and NWs, resulting in nonlinear variations in band gap and hole effective mass at VBM. Unlike the bulk phase, the critical strain of NWs highly depends on the character of the VBM state in the unstrained case, which is closely related to the size and facet of NWs. The critical strain of bulk is at compressive range, while the critical strain of NWs with HH-like and CH-like VBM appears at compressive and tensile strain, respectively. Due to the HH–CH band crossing, the charge distribution of the VBM state in NWs can also be tuned by the external uniaxial strain. Despite the complication of the VBM state, the electron effective mass at conduction band minimum（CBM） of NWs shows a linear relation with the CBM–HH energy difference, the same as the bulk material.展开更多
Electronic and magnetic properties of CeN are investigated using first-principles calculations based on density func- tional theory （DFT） with the LDA ＋ U method. Our results show that CeN is a half-metal. The majo...Electronic and magnetic properties of CeN are investigated using first-principles calculations based on density func- tional theory （DFT） with the LDA ＋ U method. Our results show that CeN is a half-metal. The majority-spin electron band structure has metallic intersections, whereas the minority-spin electron band structure has a semiconducting gap straddling the Fermi level. A small indirect energy gap occurs between X and W. The calculated magnetic moment is 0.99 μb per unit cell.展开更多
文摘I had the privilege and the pleasure to work closely with Stephen J. Pennycook for about twenty years, having a group of post-docs and Vanderbilt-University graduate students embedded in his electron microscopy group at Oak Ridge National Laboratory, spending on average a day per week there. We combined atomic-resolution imaging of materials,electron-energy-loss spectroscopy, and density-functional-theory calculations to explore and elucidate diverse materials phenomena, often resolving long-standing issues. This paper is a personal perspective of that journey, highlighting a few examples to illustrate the power of combining theory and microscopy and closing with an assessment of future prospects.
基金supported by the the National Key R&D Program of China(No.2021YFC2900800)National Natural Science Foundation of China(Nos.52425406,51874247,51922091,and 52204285)+4 种基金the Open Research Fund of State Key Laboratory of Complex Nonferrous Metal Resources Clean Utilization(No.CNMRCUKF2001)Science and Technology Major Project of Ordos City-Iconic Innovation Team and “Rejuvenating Inner Mongolia through Science and Technology”(No.202204/2023)Yueqi Outstanding Scholar Award of CUMTB(No.202022)Funded by Open Foundation of State Key Laboratory of Mineral Processing(No.BGRIMM-KJSKL-2023-05)Fundamental Research Funds for the Central Universities(Ph.D.Top Innovative Talents Fund of CUMT BBJ2024048)。
文摘Effectively separating bastnaesite from calcium-bearing gangue minerals(particularly calcite)presents a formidable challenge,making the development of efficient collectors crucial.To achieve this,we have designed and synthesized a novel,highly efficient,water-soluble cationic collector,N-dodecylisopropanolamine(NDIA),for use in the bastnaesite-calcite flotation process.Density functional theory(DFT)calculations identified the amine nitrogen atom in NDIA as the site most susceptible to electrophilic attack and electron loss.By introducing an OH group into the traditional collector dodecylamine(DDA)structure,NDIA provided additional adsorption sites,enabling synergistic adsorption on the surface of bastnaesite,thereby significantly enhancing both the floatability and selectivity of these minerals.The recovery of bastnaesite was 76.02%,while the calcite was 1.26%.The NDIA markedly affected the zeta potential of bastnaesite,while its impact on calcite was relatively minor.Detailed Fourier-transform infrared spectroscopy(FTIR)and X-ray photoelectron spectroscopy(XPS)results elucidated that the―NH―and―OH groups in NDIA anchored onto the bastnaesite surface through robust electrostatic and hydrogen bonding interactions,thereby enhancing bastnaesite's affinity for NDIA.Furthermore,in situ atomic force microscopy(AFM)provided conclusive evidence of NDIA aggregation on the bastnaesite surface,improving contact angle and hydrophobicity,and significantly boosting the flotation recovery of bastnaesite.
基金Project support by the National Key R&D Program of China(Grant Nos.2017YFB0701501,2017YFB0701502,and 2017YFB0701503)
文摘Using high-throughput first-principles calculations, we systematically studied the synergistic effect of alloying two elements （AI and 28 kinds of 3d, 4d, and 5d transition metals） on the elastic constants and elastic moduli of γ-Ni. We used machine learning to theoretically predict the relationship between alloying concentration and mechanical properties, giving the binding energy between the two elements. We found that the ternary alloying elements strengthened the 7 phase in the order of Re 〉 Ir 〉 W 〉 Ru 〉 Cr 〉 Mo 〉 Pt 〉 Ta 〉 Co. There is a quadratic parabolic relationship between the number of d shell electrons in the alloying element and the bulk modulus, and the maximum bulk modulus appears when the d shell is half full. We found a linear relationship between bulk modulus and alloying concentration over a certain alloying range. Using linear regression, we found the linear fit concentration coefficient of 29 elements. Using machine learning to theoretically predict the bulk modulus and lattice constants of Ni32XY, we predicted values close to the calculated results, with a regression parameter of R2 = 0.99626. Compared with pure Ni, the alloyed Ni has higher bulk modulus B, G, E, Cll, and C44, but equal Cl2. The alloying strengthening in some of these systems is closely tied to the binding of elements, indicating that the binding energy of the alloy is a way to assess its elastic properties.
文摘The paper presents analysis of the performance and the internal flow behaviour in the vaned diffuser of a radial flow pump using PIV(particle image velocimetry)and pressure probe traverses.PIV measurements have already been performed at middle height inside one diffuser channel passage for a given speed of rotation and various mass flow rates.These results have been already presented in several previous communications.New experiments have been performed using a three-hole pressure probe traverses from hub to shroud diffuser width at different radial locations between the two diffuser geometrical throats.Numerical simulations are also realized with the commercial codes Star CCM+7.02.011 and CFX.Frozen rotor and fully unsteady calculations of the whole pump have been performed.Comparisons between numerical results,previous experimental PIV results and new probe traverses one's are presented and discussed for one mass flow rate.In this respect,a first attempt to take into account fluid leakages between the rotating and fixed part of the pump has been checked since it may affects the real flow structure inside the diffuser.
文摘The structural, electronic, optical and thermodynamic properties of Mo2Ga2C are investigated using density func- tional theory （DFT） within the generalized gradient approximation （GGA）. The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states （DOS） is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per eV. Technologically important optical parameters （e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function） are calculated for the first time. The study of dielectric constant （ε1） indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic. The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo2Ga2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of Tc expression using available parameter values （DOS, Debye temperature, atomic mass, etc.） suggests that the compound is less likely to be superconductor.
基金supported by the National Natural Science Foundation of China(No.11875128).
文摘Nuclear data are the cornerstones of reactor physics and shielding calculations.Recently,China released CENDL-3.2 in 2020,and the US released ENDF/B-VIII.0 in 2018.Therefore,it is necessary to comprehensively evaluate the criticality computing performance of these newly released evaluated nuclear libraries.In this study,we used the NJOY2016 code to generate ACE format libraries based on the latest neutron data libraries(including CENDL-3.2,JEFF3.3,ENDF/B-VIII.0,and JENDL4.0).The MCNP code was used to conduct a detailed analysis of fission nuclides,including^(235)U,^(233)U,and^(239)Pu,in different evaluated nuclear data libraries based on 100 benchmarks.The criticality calculation performance of each library was evaluated using three statistical parameters:δk/σ,χ^(2),and<|Δ|>.Analysis of theδk/σparameter showed that CENDL-3.1 and JENDL-4.0 both had>10 benchmarks that exceeded 3r,whereas CENDL3.2,ENDFB-VIII.0,and JEFF-3.3 had,7,5,and 4 benchmarks,respectively,exceeding 3r.The ENDF/B-VII.1 library performed best,with only two benchmarks exceeding 3r.Compared to CENDL-3.1,CENDL-3.2 offers an improvement in criticality calculations.Compared to the JEFF-3.3 and ENDF/B-VIII.0 libraries,CENDL3.2 performs better in the calculation of the^(233)U assemblies,but it performs poorly in the pusl11 series case calculation of the^(239)Pu assemblies,and thus further improvement is needed.
基金supported by the National Natural Science Foundation of China(Grant No.51071032)
文摘Mechanical, electronic, and thermodynamic properties of zirconium carbide have been systematically studied using the ab initio calculations. The calculated equilibrium lattice parameter, bulk modulus, and elastic constants are all well consistent with the experimental data. The electronic band structure indicates that the mixture of C 2p and Zr 4d and 4p orbitals around the Fermi level makes a large covalent contribution to the chemical bonds between the C and Zr atoms. The Bader charge analysis suggests that there are about 1.71 electrons transferred from each Zr atom to its nearest C atom. Therefore, the Zr-C bond displays a mixed ionic/covalent character. The calculated phonon dispersions of ZrC are stable, coinciding with the experimental measurement. A drastic expansion in the volume of ZrC is seen with increasing temperature, while the bulk modulus decreases linearly. Based on the calculated phonon dispersion curves and within the quasi-harmonic approximation, the temperature dependence of the heat capacities is obtained, which gives a good description compared with the available experimental data.
基金Project supported by Tianjin Natural Science Fund, China （Grant No. 13JCQNJC00500）, the Fundamental Research Funds for the Central Universities, China （Grant No. 65012031）, and Tianjin Key Technology R＆D Program, China （Grant No. 11ZCKFGX01300）.
文摘The geometry, electronic structure and magnetic property of the hexagonal AlN(h-AlN) sheet doped by 5d atoms(Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) are investigated by first-principles calculations based on the density functional theory. The influence of symmetry and symmetry-breaking is also studied. There are two types of local symmetries of the doped systems: C3v and D3h. The symmetry will deviate from exact C3v and D3h for some particular dopants after optimization. The total magnetic moments of the doped systems are 0μBfor Lu, Ta and Ir; 1μB for Hf, W, Pt and Hg; 2μB for Re and Au; and 3μB for Os and Al-vacancy. The total densities of state are presented, where impurity energy levels exist. The impurity energy levels and total magnetic moments can be explained by the splitting of 5d orbitals or molecular orbitals under different symmetries.
基金Project supported by the National Natural Science Foundation of China(Grant No.11864011)the Hubei Provincial Natural Science Foundation of China(Grant No.2018CFB390)the Doctoral Fund Project of Hubei Minzu University,China(Grant No.MY2017B015)
文摘Heterostructures(HSs)have attracted significant attention because of their interlayer van der Waals interactions.The electronic structures and optical properties of stacked GaN-MoS2 HSs under strain have been explored in this work using density functional theory.The results indicate that the direct band gap(1.95 e V)of the Ga N-MoS2 HS is lower than the individual band gaps of both the GaN layer(3.48 e V)and the MoS2 layer(2.03 eV)based on HSE06 hybrid functional calculations.Specifically,the GaN-MoS2 HS is a typical type-II band HS semiconductor that provides an effective approach to enhance the charge separation efficiency for improved photocatalytic degradation activity and water splitting efficiency.Under tensile or compressive strain,the direct band gap of the GaN-MoS2 HS undergoes redshifts.Additionally,the GaN-MoS2 HS maintains its direct band gap semiconductor behavior even when the tensile or compressive strain reaches 5%or-5%.Therefore,the results reported above can be used to expand the application of Ga N-MoS2 HSs to photovoltaic cells and photocatalysts.
基金Supported by the National Natural Science Foundation of China under Grant Nos 11874328 and 11372283
文摘We study the negative thermal expansion(NTE) properties and effect of Na insertion on the NTE of the framework material GaFe(CN)_6 by first-principles calculations based on density functional theory within the quasi-harmonic approximation. The calculated results show that the material exhibits NTE due to the low transverse vibrational modes of the CN groups. The modes demonstrate larger negative values of the mode Grüneisen parameters. Once Na is introduced in the framework of the material, it prefers to locate at the center of the quadrates of the framework material and binds to the four N anions nearby. As a consequence, the transverse vibrational mode of the CN group is clearly hindered and the NTE of the material is weakened. Our theoretical calculations have clarified the mechanisms of NTE and the effect of the guest Na on the NTE of the framework material.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174030 and 11504020)the Fundamental Research Funds for the Central Universities of China(Grant No.FRF-TP-16-064A1,06500031)
文摘The elastic, magnetoelastic, and phonon properties of Ni2FeGa were investigated through first-principles calculations. The obtained elastic and phonon dispersion curves for the austenite and martensite phases agree well with available the- oretical and experimental results. The isotropic elastic moduli are also predicted along with the polycrystalline aggregate properties including the bulk modulus, shear modulus, Young＇s modulus, and Poisson＇s ratio. The Pugh ratio indicates that Ni2FeGa shows ductility, especially the austenite phase, which is consistent with the experimental results. The Debye tem- peratures of the Ni2FeGa in the austenite and martensite phases are 344 K and 392 K, respectively. It is predicted that the magnetoelastic coefficient is -5.3 x 10^6 J/m3 and magnetostriction coefficient is between 135 and 55 ppm in the Ni2FeGa austenite phase.
基金Project supported by the Natural Science Foundation of Jiangxi Province,China(Grant Nos.20152ACB21014,20151BAB202006,and 20142BAB212002)the Fund from the Jiangxi Provincial Educational Committee,China(Grant No.GJJ14254)supported by the Oversea Returned Project from the Ministry of Education,China
文摘The adsorption and diffusion behaviors of alkali and alkaline-earth metal atoms on silicane and silicene are both investigated by using a first-principles method within the frame of density functional theory.Silicane is staler against the metal adatoms than silicene.Hydrogenation makes the adsorption energies of various metal atoms considered in our calculations on silicane significantly lower than those on silicene.Similar diffusion energy barriers of alkali metal atoms on silicane and silicene could be observed.However,the diffusion energy barriers of alkali-earth metal atoms on silicane are essentially lower than those on silicene due to the small structural distortion and weak interaction between metal atoms and silicane substrate.Combining the adsorption energy with the diffusion energy barriers,it is found that the clustering would occur when depositing metal atoms on perfect hydrogenated silicene with relative high coverage.In order to avoid forming a metal cluster,we need to remove the hydrogen atoms from the silicane substrate to achieve the defective silicane.Our results are helpful for understanding the interaction between metal atoms and silicene-based two-dimensional materials.
文摘The dielectric constant(DC)is one of the key properties for detection of threat materials such as Improvised Explosive Devices(IEDs).In the present paper,the density functional theory(DFT)as well as ab-initio approaches are used to explore effective methods to predict dielectric constants of a series of 12 energetic materials(EMs)for which experimental data needed to experimentally determine the dielectric constant(refractive indices)are available.These include military grades energetic materials,nitro and peroxide compounds,and the widely used nitroglycerin.Ab-initio and DFT calculations are conducted.In order to calculate dielectric constant values of materials,potential DFT functional combined with basis sets are considered for testing.Accuracy of the calculations are compared to experimental data listed in the scientific literature,and time required for calculations are both evaluated and discussed.The best functional/basis set combinations among those tested are CAM-B3LYP and AUG-ccpVDZm,which provide great results,with accuracy deviations below 5%when calculated results are compared to experimental data.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61475132 and 61501392
文摘The recently discovered tetragonal, monoclinie and orthorhombic polymorphs of M3N4 （M=C, Si, Sn） are in- vestigated by using first-principles calculations. A set of anisotropic elastic quantities, i.e., the bulk and shear moduli, Young＇s modulus, Poisson ratio, H/G ratio and rickets hardness of M3N4 （M=C, Si, Sn） are predicted. The quasi-harmonic Debye model, assuming that the solids are isotopic, may lead to large errors for the non-cubic crystals. The thermal effects are obtained by the traditional quasi-harmonic approach. The dependences of heat capacity, thermal expansion coefficient and Debye temperature on temperature and pressure are systematically discussed in the pressure range of 0 IOGPa and in the temperature range of 0-1100 K. More importantly, o- C3N4 is a negative thermal expansion material. Our results may have important consequences in shaping the understanding of the fundamental properties of these binary nitrides.
基金Project supported by Chongqing Natural Science Foundation,China (Grant Nos.CSCT2010BB4405 and CSTC2008BB4083)the Doctoral Foundation of Chongqing University of Posts and Telecommunications,China(Grant No.A2008-63)
文摘Several rocksalt Sr4X3N （X = O, S, Se, and Te） are predicted to be potential half-metallic ferromagnets free of transition-metal and rare-earth elements by performing the first-principles calculations. Then their magnetic properties, such as the half metallicity and the crystal-cell magnetic moments are investigated. The Sr4X3N possibly have higher Curie temperatures and have more stable half metallicity than the Sr4X3C. Their crystal-cell magnetic moments are all 1.00 μB. The crystal-cell magnetic moments and the half metallicity arise mainly from the N ions. The main mechanism is the strong covalent interaction leading to the sp2 hybridized orbitals in the Sr4X3N. Then two Sr-5s and three N-2p electrons enter into three sp2 hybridized orbitals. Among these five electrons, four electrons are paired and one is unpaired, so there are three spin-up electrons and two spin-down electrons in these sp2 hybridized orbitals.
基金Project supported by the Research Project of Islamic Azad University,Urmia Branch
文摘We employed ab-initio calculations to investigate the structural and thermodynamic properties of Massicot or orthorhombic phase of PbO named β-PbO using the projector augmented-wave（PAW） method within the generalized gradient approximation（GGA）. The temperature and pressure dependence of bulk modulus, heat capacity at constant pressure and constant volume, entropy, thermal expansion coefficient and Grüneisen parameter were discussed. Accuracy of two different models, the Debye and Debye-Grüneisen which are based on the quasi-harmonic approximation（QHA） for producing thermodynamic properties of material were compared. According to calculation results, these two models can be used to designate thermodynamic properties for β-PbO with sensible accuracy over a wide range of temperatures and pressures, and our work on the properties of this structure will be useful for more deeply understanding various properties of this structure.
基金Project supported by the National Key Research and Development Program of China(Grant No.2017YFB0701503)。
文摘The phase partition and site preference of Re atoms in a ternary Ni-Al-Re model alloy,including the electronic structure of different Re configurations,are investigated with first-principles calculations and atom probe tomography.The Re distribution of single,nearest neighbor(NN),next-nearest neighbor(NNN),and cluster configurations are respectively designed in the models withγandγphases.The results show that the Re atoms tend to enteringγphase and the Re atoms prefer to occupy the Al sites inγphase.The Re cluster with a combination of NN and NNN Re-Re pair configuration is not preferred than the isolated Re atom in the Ni-based superalloys,and the configuration with isolated Re atom is more preferred in the system.Especially,the electronic states are analyzed and the energetic parameters are calculated.The electronic structure analyses show there exists strong Ni-Re electronic interaction and it is mainly contributed by the d-d hybridization.The characteristic features of the electronic states of the Re doping effects are also given.It is also found that Re atoms prefer the Al sites inγside at the interface.The density of states at or near the Fermi level and the d-d hybridizations of NN Ni-Re are found to be important in the systems.
基金Supported by the National Natural Science Foundation of China under Grant No 11572040the Thousand Young Talents Program of Chinathe Special Program for Applied Research on Super Computation of the NSFC-Guangdong Joint Fund(second phase)under Grant No U1501501
文摘The mechanical properties of formamidinium halide perovskites FABX_3(FA=CH(NH_2)_2; B=Pb, Sn; X=Br, I)are systematically investigated using first-principles calculations. Our results reveal that FABX_3 perovskites possess excellent mechanical flexibility, ductility and strong anisotropy. We shows that the planar organic cation FA+ has an important effect on the mechanical properties of FABX3 perovskites. In addition, our results indicate that (i) the moduli(bulk modulus B, Young's modulus E, and shear modulus G) of FABBr_3 are larger than those of FABI_3 for the same B atom, and (ii) the moduli of FAPbX_3 are larger than those of FASnX_3 for the same halide atom. The reason for the two trends is demonstrated by carefully analyzing the bond strength between B and X atoms based on the projected crystal orbital Hamilton population method.
基金supported by the National Natural Science Foundation of China(Grant Nos.11204296 and 61427901)the National Basic Research Program of China(Grant Nos.2014CB643902 and 2013CB933304)
文摘sing first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX（X = S, Se, Te） bulk and nanowires（NWs） under uniaxial [0001] strain. Due to the intrinsic shrinking strain induced by surface contraction, large NWs with {10ˉ10} facets have heavy hole（HH）-like valence band maximum（VBM） states, while NWs with {11ˉ20} facets have crystal hole（CH）-like VBM states. The external uniaxial strain induces an HH–CH band crossing at a critical strain for both bulk and NWs, resulting in nonlinear variations in band gap and hole effective mass at VBM. Unlike the bulk phase, the critical strain of NWs highly depends on the character of the VBM state in the unstrained case, which is closely related to the size and facet of NWs. The critical strain of bulk is at compressive range, while the critical strain of NWs with HH-like and CH-like VBM appears at compressive and tensile strain, respectively. Due to the HH–CH band crossing, the charge distribution of the VBM state in NWs can also be tuned by the external uniaxial strain. Despite the complication of the VBM state, the electron effective mass at conduction band minimum（CBM） of NWs shows a linear relation with the CBM–HH energy difference, the same as the bulk material.
基金Project supported by the National Basic Research Program of China(Grant Nos.2010CB731600 and 2010CB731604-2)
文摘Electronic and magnetic properties of CeN are investigated using first-principles calculations based on density func- tional theory （DFT） with the LDA ＋ U method. Our results show that CeN is a half-metal. The majority-spin electron band structure has metallic intersections, whereas the minority-spin electron band structure has a semiconducting gap straddling the Fermi level. A small indirect energy gap occurs between X and W. The calculated magnetic moment is 0.99 μb per unit cell.
