Low dimensional materials are suitable candidates applying in next-generation high-performance electronic,optoelectronic,and energy storage devices because of their uniquely physical and chemical properties.In particu...Low dimensional materials are suitable candidates applying in next-generation high-performance electronic,optoelectronic,and energy storage devices because of their uniquely physical and chemical properties.In particular,one-dimensional(1D)atomic wires(AWs)exfoliating from 1D van der Waals(vdW)bulks are more promising in next generation nanometer(nm)even sub-nm device applications owing to their width of few-atoms scale and free dandling bonds states.Although several 1D AWs have been experimentally prepared,few 1D AW candidates could be practically applied in devices owing to lack of enough suitable 1D AWs.Herein,367 kinds of 1D AWs have been screened and the corresponding computational database including structures,electronic structures,magnetic states,and stabilities of these 1D AWs has been organized and established.Among these systems,unary and binary 1D AWs with relatively small exfoliation energy are thermodynamically stable and theoretically feasible to be exfoliated.More significantly,rich quantum states emerge,such as 1D semiconductors,1D metals,1D semimetals,and 1D magnetism.This database will offer an ideal platform to further explore exotic quantum states and exploit practical device applications using 1D materials.The database are openly available at http://www.dx.doi.org/10.11922/sciencedb.j00113.00004.展开更多
The structural, anisotropic elastic properties and the ideal compressive and tensile strengths of titanium diboride （TiB2） were investigated using first-principles calculations based on density functional theory. Th...The structural, anisotropic elastic properties and the ideal compressive and tensile strengths of titanium diboride （TiB2） were investigated using first-principles calculations based on density functional theory. The stress-strain relationships of TiB2 under 〈10i0〉, 〈12i0〉, and 〈0001〉 compressive loads were calculated. Our results showed that the ideal uniaxial compressive strengths are ｜σ〈02i0〉）｜ = 142.96 GPa, ｜σ〈0001〉 ] = 188.75 GPa, and ｜σ〈10i0〉｜ = 245.33 GPa, at strains -0.16, -0.32, and -0.24, respectively. The variational trend is just the opposite to that of the ideal tensile strength with σ〈10i0〉 = 44.13 GPa, σ〈0001〉 = 47.03 GPa, and σ〈i2i0〉 = 56.09 GPa, at strains 0.14, 0.28, and 0.22, respectively. Furthermore, it was found that TiB2 is much stronger under compression than in tension. The ratios of the ideal compressive to tensile strengths are 5.56, 2.55, and 4.01 for crystallographic directions （10i0）, 〈12i0〉, and 〈0001〉, respectively. The present results are in excellent agreement with the most recent experimental data and should be helpful to the understanding of the compressive property of TiB2.展开更多
The global greenhouse effect makes it urgent to deal with the increasing greenhouse gases. In this paper the performance of MgO-decorated carbon nanotubes for CO2 adsorption is investigated through first principles ca...The global greenhouse effect makes it urgent to deal with the increasing greenhouse gases. In this paper the performance of MgO-decorated carbon nanotubes for CO2 adsorption is investigated through first principles calculations. The results show that the MgO-decorated carbon nanotubes can adsorb CO2 well and are relatively insensitive to O2 and N2 at the same time. The binding energy arrives at 1.18 eV for the single-MgO-decorated carbon nanotube adsorbing one CO2 molecule, while the corresponding values for O2 and N2 are 0.55 eV and 0.06 eV, respectively. In addition, multi-molecule adsorption is also proved to be very satisfactory. These results indicate that MgO-decorated carbon nanotubes have great potential applications in industrial and environmental processes.展开更多
Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been ...Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been successfully synthesized.Herein,we study the TE properties of this bulk Au2S by first-principles calculations and semiclassical Boltzmann transport theory,which provides the basis for its further experimental studies.Our results indicate that the highly twofold degeneracy of the bands appears at theΓpoint in the Brillouin zone,resulting in a high Seebeck coefficient.Besides,Au2S exhibits an ultra-low lattice thermal conductivity(~0.88 W·m^-1·K^-1 at 700 K).At 700 K,the thermoelectric figure of merit of the optimal p-type doping is close to 1.76,which is higher than 0.8 of ZrSb at 700 K and 1.4 of PtTe at 750 K.Our work clearly demonstrates the advantages of Au2S as a TE material and would greatly inspire further experimental studies and verifications.展开更多
In this study the pseudo-potential method is used to investigate the structural, electronic, and thermodynamic proper- ties of ZnOl_xSx semiconductor materials. The results show that the electronic properties are foun...In this study the pseudo-potential method is used to investigate the structural, electronic, and thermodynamic proper- ties of ZnOl_xSx semiconductor materials. The results show that the electronic properties are found to be improved when calculated by using LDA ~ U functional as compared with local density approximation （LDA）. At various concentrations the ground-state properties are determined for bulk materials ZnO, ZnS, and their tertiary alloys in cubic zinc-blende phase. From the results, a minor difference is observed between the lattice parameters from Vegard＇s law and other calculated results, which may be due to the large mismatch between lattice parameters of binary compounds ZnO and ZnS. A small deviation in the bulk modulus from linear concentration dependence is also observed for each of these alloys. The ther- modynamic properties, including the phonon contribution to Helmholtz free energy △F, phonon contribution to internal energy △E, and specific iheat at constant-volume Cv, are calculated within quasi-harmonic approximation based on the calculated phonon dispersion relations.展开更多
The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of Cd Se_（1-x）Te_x in the zinc blende phase. It is observed that the electronic properties are improv...The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of Cd Se_（1-x）Te_x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA ＋ U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure Cd Se and Cd Te binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature.展开更多
To maximize the catalytic performance of MoS_(2) in the hydrogen evolution reaction,we investigate the electrocatalytic and photocatalytic performance of monolayer MoS_(2) doped with noble metal(Ag,Au,Cu,Pd,and Pt)usi...To maximize the catalytic performance of MoS_(2) in the hydrogen evolution reaction,we investigate the electrocatalytic and photocatalytic performance of monolayer MoS_(2) doped with noble metal(Ag,Au,Cu,Pd,and Pt)using first principles calculation combined with the climbing image nudged elastic band method.We find the band gap of the monolayer MoS_(2) is reduced significantly by the noble metal doping,which is unfavorable to improving its photocatalytic performance.The optical absorption coefficient shows that the doping does not increase the ability of the monolayer MoS_(2) to absorb visible light.The monolayer MoS_(2) doped with the noble metal is not a potential photocatalyst for the hydrogen evolution reaction because the band edge position of the conduction band minimum is lower than-4.44 eV,the reduction potential of H^(+)/H_(2).Fortunately,the band gap reduction increases the electron transport performance of the monolayer MoS_(2),and the activation energy of water splitting is greatly reduced by the noble metal doping,especially the Pt doping.On the whole,noble metal doping can enhance the electrocatalytic performance of the monolayer MoS_(2).展开更多
The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta al...The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta alloys was analysed by the projected density of states(PDOS).The low temperature heat capacity was estimated by Fermi energy and Debye temperature.It is shown that the formation enthalpy will decrease with the increase of Ta content,and the cohesive energy will increase with the increase of the Ta content.On the other hand,the addition of Ta atoms will reduce the strength and improve the ductility of Mo-Ta alloys,the Debye temperature will decrease and the low temperature heat capacity will be improved with the increase of the Ta content.All these results will be useful for the research of new plasma grid(PG)materials,which is mainly used in neutral beam injection(NBI)systems to produce negative hydrogen ions.展开更多
An important challenge facing K-ion batteries lies in exploring earth-abundant and safe cathode materials that can provide high capacity with high migration rate of K ions.Here,we propose a simple and efficient method...An important challenge facing K-ion batteries lies in exploring earth-abundant and safe cathode materials that can provide high capacity with high migration rate of K ions.Here,we propose a simple and efficient method for searching potential K cathode materials with first principles calculations.Our screening is based on combinations of weight capacity,K ion occupation ratio,volume change per K,and valence limit.With this screening method we predicted a series of potential K ions cathodes with favorable electrochemical performance,such as K_(2)VPO_(4)CO_(3)-like structures with 1 D diffusion channels,3 D channel structures K_(2)CoSiO_(4),layered materials KCoO_(2),KCrO_(2),KVF_(4) and K_(5)V_(3)F_(14),and others.These potential cathodes have small volume changes,suitable voltage,and high capacity,with small diffusion barriers.They may be useful in K-ion batteries with high energy density and rate performance.展开更多
In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties, in which directional optical properties can be exploited to enhance the performance of optoelectronic...In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties, in which directional optical properties can be exploited to enhance the performance of optoelectronic devices. First principles calculation based on density functional theory （DFT） with the generalized gradient approximation （GGA） are carried out to investigate the energy band gap structure on silicon （Si） and germanium （Ge） nanofilms. Simulation results show that the band gaps in Si （100） and Ge （111） nanofilms become the direct-gap structure in the thickness range less than 7.64 nm and 7.25 nm respectively, but the band gaps of Si （111） and Ge （110） nanofilms still keep in an indirect-gap structure and are independent on film thickness, and the band gaps of Si （110） and Ge （100） nanofilms could be transferred into the direct-gap structure in nanofilms with smaller thickness. It is amazing that the band gaps of Si（1-x）/ZGexSi（1-x）/2 sandwich structure become the direct-gap structure in a certain area whether （111） or （100） surface. The band structure change of Si and Ge thin films in three orientations is not the same and the physical mechanism is very interesting, where the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects.展开更多
The intercalation of heteroatoms between graphene and metal substrates is a promising method for integrating epitaxial graphene with functional materials.Various elements and their oxides have been successfully interc...The intercalation of heteroatoms between graphene and metal substrates is a promising method for integrating epitaxial graphene with functional materials.Various elements and their oxides have been successfully intercalated into graphene/metal interfaces to form graphene-based heterostructures,showing potential applications in electronic devices.Here we theoretically investigate the hafnium intercalation between graphene and Ir(111).It is found that the penetration barrier of Hf atom is significantly large due to its large atomic radius,which suggests that hafnium intercalation should be carried out with low deposition doses of Hf atoms and high annealing temperatures.Our results show the different intercalation behaviors of a large-size atom and provide guidance for the integration of graphene and hafnium oxide in device applications.展开更多
Recently,metal-graphene nanocomposite system has aroused much interest due to its radiation tolerance behavior.However,the related atomic mechanism for the metal-graphene interface is still unknown.Further,stainless s...Recently,metal-graphene nanocomposite system has aroused much interest due to its radiation tolerance behavior.However,the related atomic mechanism for the metal-graphene interface is still unknown.Further,stainless steels with Fe as main matrix are widely used in nuclear systems.Therefore,in this study,the atomic behaviors of point defects and helium(He) atoms at the Fe(110)-graphene interface are investigated systematically by first principles calculations.The results indicate that graphene interacts strongly with the Fe(110) substrate.In comparison with those of the original graphene and bulk Fe,the formation energy values of C vacancies and Fe point defects decrease significantly for Fe(110)-graphene.However,as He atoms have a high migration barrier and large binding energy at the interface,they are trapped at the interface once they enter into it.These theoretical results suggest that the Fe(110)-graphene interface acts as a strong sink that traps defects,suggesting the potential usage of steel-graphene with multiply interface structures for tolerating the radiation damage.展开更多
Double perovskite Bi2 FeCrO6 , related with multiferroic BiFeO3 , is very interesting because of its strong ferroelectricity and high magnetic Curie temperature beyond room temperature. We investigate its electronic s...Double perovskite Bi2 FeCrO6 , related with multiferroic BiFeO3 , is very interesting because of its strong ferroelectricity and high magnetic Curie temperature beyond room temperature. We investigate its electronic structure and magnetic and optical properties by using a full-potential density-functional method. Our optimization shows that it is a robust ferrimagnetic semiconductor. This nonmetallic phase is formed due to crystal field splitting and spin exchange splitting, in contrast to previous studies. Spin exchange constants and optical properties are calculated. Our Monte Carlo magnetic Curie temperature is 450 K, much higher than any previously calculated value and consistent with experimental results. Our study and analysis reveal that the main magnetic mechanism is an antiferromagnetic superexchange between Fe and Cr over the intermediate O atom. These results are useful in understanding such perovskite materials and exploring their potential applications.展开更多
Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coatin...Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials.In this paper,we present a first-principles calculations of the phonon transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers.Both materials possess low lattice thermal conductivity,at least two orders of magnitude lower than graphene and h-BN.The room temperature thermal conductivity of Pb_(2)SbAs(0.91 W/m K)is only a quarter of that of Pb_(2)PAs(3.88 W/m K).We analyze in depth the bonding,lattice dynamics,and phonon mode level information of these materials.Ultimately,it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures.Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb_(2)PAs and Pb_(2)SbAs,and the three-phonon scattering is sufficient to describe their anharmonicity.In this study,the thermal transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers are illuminated based on fundamental physical mechanisms,and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.展开更多
Titanium dioxide(TiO_(2))has attracted considerable research attentions for its promising applications in solar cells and photocatalytic devices.However,the intrinsic challenge lies in the relatively low energy conver...Titanium dioxide(TiO_(2))has attracted considerable research attentions for its promising applications in solar cells and photocatalytic devices.However,the intrinsic challenge lies in the relatively low energy conversion efficiency of TiO_(2),primarily attributed to the substantial band gaps(exceeding 3.0 eV)associated with its rutile and anatase phases.Leveraging multi-objective global optimization,we have identified two quasi-layered ternary Ti-O-S crystals,composed of titanium,oxygen,and sulfur.The calculations of formation energy,phonon dispersions,and thermal stability confirm the chemical,dynamical and thermal stability of these newly discovered phases.Employing the state-of-art hybrid density functional approach and many-body perturbation theory(quasiparticle GW approach and Bethe-Salpeter equation),we calculate the optical properties of both the TiOS phases.Significantly,both phases show favorable photocatalytic characteristics,featuring band gaps suitable for visible optical absorption and appropriate band alignments with water for effective charge carrier separation.Therefore,ternary compound TiOS holds the potential for achieving high-efficiency photochemical conversion,showing our multi-objective global optimization provides a new approach for novel environmental and energy materials design with multicomponent compounds.展开更多
To design the high-energy-density Li-ion batteries, the anode materials with high specific capacity haveattracted much attention. In this work, we adopt the first principles calculations to investigate the pos-sibilit...To design the high-energy-density Li-ion batteries, the anode materials with high specific capacity haveattracted much attention. In this work, we adopt the first principles calculations to investigate the pos-sibility of a new two dimensional boron material, named Be, as anode material for Li-ion batteries. Thecalculated results show that the maximum theoretical specific capacity of Bc is 1653mAh g-1 （LiBl.s）.Additionally, the energy barriers of Li ion and Li vacancy diffusion are 330 meV and 110 meV, respec-tively, which imply fast charge and discharge ability for B6 as an anode material. The theoretical findingsreported in this work suggest that BG is a potential candidate as anode material of high-energy-density Li-ion batteries.展开更多
The lattice dynamics,elastic properties and the origin of vanished magnetism in equiatomic quaternary Heusler compounds CoMnVZ(Z=Al,Ga)are investigated by first principle calculations in this work.Due to the similar c...The lattice dynamics,elastic properties and the origin of vanished magnetism in equiatomic quaternary Heusler compounds CoMnVZ(Z=Al,Ga)are investigated by first principle calculations in this work.Due to the similar constituent atoms in CoMnVAl and CoMnVGa compounds,they are both stable in LiMgPdSn-type structure with comparable lattice size,phonon dispersions and electronic structures.Comparatively,we find that CoMnVAl is more structurally stable than CoMnVGa.Meanwhile,the increased covalent bonding component in CoMnVAl enhances its mechanical strength and Vickers hardness,which leads to better comprehensive mechanical properties than those of CoMnVGa.Practically and importantly,structural and chemical compatibilities at the interface make non-magnetic semiconductor CoMnVAl and magnetic topological semimetals Co2MnAl/Ga more suitable to be grown in heterostructures.Owing to atomic preferential occupation in CoMnVAl/Ga,the localized atoms Mn occupy C(0.5,0.5,0.5)Wyckoff site rather than B(0.25,0.25,0.25)and D(0.75,0.75,0.75)Wyckoff sites in LiMgPdSn-type structure,which results in symmetric band filling and consequently drives them to be non-magnetic.Correspondingly,by tuning localized atoms Mn to occupy B(0.25,0.25,0.25)or/and D(0.75,0.75,0.75)Wyckoff sites in off-stoichiometric Co-Mn-V-Al/Ga compounds and keeping the total valence electrons as 24,newly compensated ferrimagnetic compounds are theoretically achieved.We hope that our work will provide more choices for spintronic applications.展开更多
Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） are experimentally and theoretically investigated, The biaxial compressive strained GaSb MOSFETs show ...Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） are experimentally and theoretically investigated, The biaxial compressive strained GaSb MOSFETs show a high peak mobility of 638 cm2/V.s, which is 3.86 times of the extracted mobility of the fabricated GaSb MOSFETs without strain. Meanwhile, first principles calculations show that the hole effective mass of GaSb depends on the biaxial compressive strain. The biaxiai compressive strain brings a remarkable enhancement of the hole mobility caused by a significant reduction in the hole effective mass due to the modulation of the valence bands.展开更多
The structural, electronic, and elastic properties of ZnSe1-xSx for the zinc blende structures have been studied by using the density functional theory. The calculations were performed using the plane wave pseudopoten...The structural, electronic, and elastic properties of ZnSe1-xSx for the zinc blende structures have been studied by using the density functional theory. The calculations were performed using the plane wave pseudopotential method, as implemented in Quantum ESPRESSO. The exchange-correlation potential is treated with the local density approximation pz-LDA for these properties. Moreover, LDA＋U approximation is employed to treat the ＂d＂ orbital electrons properly. A comparative study of the band gap calculated within both LDA and LDA＋U schemes is presented. The analysis of results show considerable improvement in the calculation of band gap. The inclusion of compositional disorder increases the values of all elastic constants. In this study, it is found that elastic constants C11, C12, and C44 are mainly influenced by the compositional disorder. The obtained results are in good agreement with literature.展开更多
In the paper, density of states, band structure and electron density difference of Zn1-xCdxO are calculated by first principles, here x varies from 0 to 0.75 at intervals of 0.125, and the band gap obtained from band ...In the paper, density of states, band structure and electron density difference of Zn1-xCdxO are calculated by first principles, here x varies from 0 to 0.75 at intervals of 0.125, and the band gap obtained from band structure changes from 0.968 eV to 0.043 eV. The lattice strain and p-d repulsion theory are used to investigate variation of the band gap, the results obtained show that the variation is mainly due to the lattice tensile strain. The p-d repulsion in Zn1-xCdxO cannot be neglected. In addition, electron density difference can be used to verify the results.展开更多
基金the National Key Research and Development Program of China(Grant No.2017YFE0129000)the National Natural Science Foundation of China(Grant Nos.51871121,11874223,and 11404172).
文摘Low dimensional materials are suitable candidates applying in next-generation high-performance electronic,optoelectronic,and energy storage devices because of their uniquely physical and chemical properties.In particular,one-dimensional(1D)atomic wires(AWs)exfoliating from 1D van der Waals(vdW)bulks are more promising in next generation nanometer(nm)even sub-nm device applications owing to their width of few-atoms scale and free dandling bonds states.Although several 1D AWs have been experimentally prepared,few 1D AW candidates could be practically applied in devices owing to lack of enough suitable 1D AWs.Herein,367 kinds of 1D AWs have been screened and the corresponding computational database including structures,electronic structures,magnetic states,and stabilities of these 1D AWs has been organized and established.Among these systems,unary and binary 1D AWs with relatively small exfoliation energy are thermodynamically stable and theoretically feasible to be exfoliated.More significantly,rich quantum states emerge,such as 1D semiconductors,1D metals,1D semimetals,and 1D magnetism.This database will offer an ideal platform to further explore exotic quantum states and exploit practical device applications using 1D materials.The database are openly available at http://www.dx.doi.org/10.11922/sciencedb.j00113.00004.
文摘The structural, anisotropic elastic properties and the ideal compressive and tensile strengths of titanium diboride （TiB2） were investigated using first-principles calculations based on density functional theory. The stress-strain relationships of TiB2 under 〈10i0〉, 〈12i0〉, and 〈0001〉 compressive loads were calculated. Our results showed that the ideal uniaxial compressive strengths are ｜σ〈02i0〉）｜ = 142.96 GPa, ｜σ〈0001〉 ] = 188.75 GPa, and ｜σ〈10i0〉｜ = 245.33 GPa, at strains -0.16, -0.32, and -0.24, respectively. The variational trend is just the opposite to that of the ideal tensile strength with σ〈10i0〉 = 44.13 GPa, σ〈0001〉 = 47.03 GPa, and σ〈i2i0〉 = 56.09 GPa, at strains 0.14, 0.28, and 0.22, respectively. Furthermore, it was found that TiB2 is much stronger under compression than in tension. The ratios of the ideal compressive to tensile strengths are 5.56, 2.55, and 4.01 for crystallographic directions （10i0）, 〈12i0〉, and 〈0001〉, respectively. The present results are in excellent agreement with the most recent experimental data and should be helpful to the understanding of the compressive property of TiB2.
基金Project supported by the National Natural Science foundation of China (Grant No.60925016)
文摘The global greenhouse effect makes it urgent to deal with the increasing greenhouse gases. In this paper the performance of MgO-decorated carbon nanotubes for CO2 adsorption is investigated through first principles calculations. The results show that the MgO-decorated carbon nanotubes can adsorb CO2 well and are relatively insensitive to O2 and N2 at the same time. The binding energy arrives at 1.18 eV for the single-MgO-decorated carbon nanotube adsorbing one CO2 molecule, while the corresponding values for O2 and N2 are 0.55 eV and 0.06 eV, respectively. In addition, multi-molecule adsorption is also proved to be very satisfactory. These results indicate that MgO-decorated carbon nanotubes have great potential applications in industrial and environmental processes.
基金the National Natural Science Foundation of China(Grant Nos.11504312,11775102,and 11805088)the National Basic Research Program of China(Grant No.2015CB921103)+2 种基金China Postdoctoral Science Foundation(Grant No.2018M641477)Guangdong Provincial Department of Science and Technology,China(Grant No.2018A0303100013)the Fundamental Research Funds for the Central Universities,China(Lanzhou University,Grant No.lzujbky-2018-19).
文摘Sulfide nanocrystals and their composites have shown great potential in the thermoelectric(TE)field due to their extremely low thermal conductivity.Recently a solid and hollow metastable Au2S nanocrystalline has been successfully synthesized.Herein,we study the TE properties of this bulk Au2S by first-principles calculations and semiclassical Boltzmann transport theory,which provides the basis for its further experimental studies.Our results indicate that the highly twofold degeneracy of the bands appears at theΓpoint in the Brillouin zone,resulting in a high Seebeck coefficient.Besides,Au2S exhibits an ultra-low lattice thermal conductivity(~0.88 W·m^-1·K^-1 at 700 K).At 700 K,the thermoelectric figure of merit of the optimal p-type doping is close to 1.76,which is higher than 0.8 of ZrSb at 700 K and 1.4 of PtTe at 750 K.Our work clearly demonstrates the advantages of Au2S as a TE material and would greatly inspire further experimental studies and verifications.
基金the Higher Education Commission of Pakistan for partial funding.
文摘In this study the pseudo-potential method is used to investigate the structural, electronic, and thermodynamic proper- ties of ZnOl_xSx semiconductor materials. The results show that the electronic properties are found to be improved when calculated by using LDA ~ U functional as compared with local density approximation （LDA）. At various concentrations the ground-state properties are determined for bulk materials ZnO, ZnS, and their tertiary alloys in cubic zinc-blende phase. From the results, a minor difference is observed between the lattice parameters from Vegard＇s law and other calculated results, which may be due to the large mismatch between lattice parameters of binary compounds ZnO and ZnS. A small deviation in the bulk modulus from linear concentration dependence is also observed for each of these alloys. The ther- modynamic properties, including the phonon contribution to Helmholtz free energy △F, phonon contribution to internal energy △E, and specific iheat at constant-volume Cv, are calculated within quasi-harmonic approximation based on the calculated phonon dispersion relations.
文摘The plane wave pseudo-potential method was used to investigate the structural, electronic, and elastic properties of Cd Se_（1-x）Te_x in the zinc blende phase. It is observed that the electronic properties are improved considerably by using LDA ＋ U as compared to the LDA approach. The calculated lattice constants and bulk moduli are also comparable to the experimental results. The cohesive energies for pure Cd Se and Cd Te binary and their mixed alloys are calculated. The second-order elastic constants are also calculated by the Lagrangian theory of elasticity. The elastic properties show that the studied material has a ductile nature.
基金the Joint Funds of the National Natural Science Foundation of China(Grant No.U1967212)the National Science and Technology Major Project of China(Grant No.2019XS06004009)the Fundamental Research Funds for the Central Universities(Grant No.2018ZD10).
文摘To maximize the catalytic performance of MoS_(2) in the hydrogen evolution reaction,we investigate the electrocatalytic and photocatalytic performance of monolayer MoS_(2) doped with noble metal(Ag,Au,Cu,Pd,and Pt)using first principles calculation combined with the climbing image nudged elastic band method.We find the band gap of the monolayer MoS_(2) is reduced significantly by the noble metal doping,which is unfavorable to improving its photocatalytic performance.The optical absorption coefficient shows that the doping does not increase the ability of the monolayer MoS_(2) to absorb visible light.The monolayer MoS_(2) doped with the noble metal is not a potential photocatalyst for the hydrogen evolution reaction because the band edge position of the conduction band minimum is lower than-4.44 eV,the reduction potential of H^(+)/H_(2).Fortunately,the band gap reduction increases the electron transport performance of the monolayer MoS_(2),and the activation energy of water splitting is greatly reduced by the noble metal doping,especially the Pt doping.On the whole,noble metal doping can enhance the electrocatalytic performance of the monolayer MoS_(2).
基金supported by National Natural Science Foundation of China(No.11820101004)the National Key R&D Program of China(2017YFE0300100,2017YFE0301100)。
文摘The mechanical properties,thermodynamic properties and electronic structure of Mo1-xTax(Mo-Ta)alloys(x=0,0.0625,0.125,0.25,0.3125,0.5 and 1)were calculated by using firstprinciples.The electronic structure of Mo-Ta alloys was analysed by the projected density of states(PDOS).The low temperature heat capacity was estimated by Fermi energy and Debye temperature.It is shown that the formation enthalpy will decrease with the increase of Ta content,and the cohesive energy will increase with the increase of the Ta content.On the other hand,the addition of Ta atoms will reduce the strength and improve the ductility of Mo-Ta alloys,the Debye temperature will decrease and the low temperature heat capacity will be improved with the increase of the Ta content.All these results will be useful for the research of new plasma grid(PG)materials,which is mainly used in neutral beam injection(NBI)systems to produce negative hydrogen ions.
基金supported by the National Key R&D Program of China(Grant No.2016YFA0200400)the National Natural Science Foundation of China(Grant No.11504123 and No.51627805)。
文摘An important challenge facing K-ion batteries lies in exploring earth-abundant and safe cathode materials that can provide high capacity with high migration rate of K ions.Here,we propose a simple and efficient method for searching potential K cathode materials with first principles calculations.Our screening is based on combinations of weight capacity,K ion occupation ratio,volume change per K,and valence limit.With this screening method we predicted a series of potential K ions cathodes with favorable electrochemical performance,such as K_(2)VPO_(4)CO_(3)-like structures with 1 D diffusion channels,3 D channel structures K_(2)CoSiO_(4),layered materials KCoO_(2),KCrO_(2),KVF_(4) and K_(5)V_(3)F_(14),and others.These potential cathodes have small volume changes,suitable voltage,and high capacity,with small diffusion barriers.They may be useful in K-ion batteries with high energy density and rate performance.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11264007 and 61465003)
文摘In nanomaterials, optical anisotropies reveal a fundamental relationship between structural and optical properties, in which directional optical properties can be exploited to enhance the performance of optoelectronic devices. First principles calculation based on density functional theory （DFT） with the generalized gradient approximation （GGA） are carried out to investigate the energy band gap structure on silicon （Si） and germanium （Ge） nanofilms. Simulation results show that the band gaps in Si （100） and Ge （111） nanofilms become the direct-gap structure in the thickness range less than 7.64 nm and 7.25 nm respectively, but the band gaps of Si （111） and Ge （110） nanofilms still keep in an indirect-gap structure and are independent on film thickness, and the band gaps of Si （110） and Ge （100） nanofilms could be transferred into the direct-gap structure in nanofilms with smaller thickness. It is amazing that the band gaps of Si（1-x）/ZGexSi（1-x）/2 sandwich structure become the direct-gap structure in a certain area whether （111） or （100） surface. The band structure change of Si and Ge thin films in three orientations is not the same and the physical mechanism is very interesting, where the changes of the band gaps on the Si and Ge nanofilms follow the quantum confinement effects.
基金Project supported by the National Natural Science Foundation of China(Grant No.61888102)the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB30000000)the Fundamental Research Funds for the Central Universities,China。
文摘The intercalation of heteroatoms between graphene and metal substrates is a promising method for integrating epitaxial graphene with functional materials.Various elements and their oxides have been successfully intercalated into graphene/metal interfaces to form graphene-based heterostructures,showing potential applications in electronic devices.Here we theoretically investigate the hafnium intercalation between graphene and Ir(111).It is found that the penetration barrier of Hf atom is significantly large due to its large atomic radius,which suggests that hafnium intercalation should be carried out with low deposition doses of Hf atoms and high annealing temperatures.Our results show the different intercalation behaviors of a large-size atom and provide guidance for the integration of graphene and hafnium oxide in device applications.
基金Project supported by the Nuclear Power Technology Innovation Center ProgramNational Defense Science&Technology Industry,China(Grant No.HDLCXZX-2019-ZH-028)。
文摘Recently,metal-graphene nanocomposite system has aroused much interest due to its radiation tolerance behavior.However,the related atomic mechanism for the metal-graphene interface is still unknown.Further,stainless steels with Fe as main matrix are widely used in nuclear systems.Therefore,in this study,the atomic behaviors of point defects and helium(He) atoms at the Fe(110)-graphene interface are investigated systematically by first principles calculations.The results indicate that graphene interacts strongly with the Fe(110) substrate.In comparison with those of the original graphene and bulk Fe,the formation energy values of C vacancies and Fe point defects decrease significantly for Fe(110)-graphene.However,as He atoms have a high migration barrier and large binding energy at the interface,they are trapped at the interface once they enter into it.These theoretical results suggest that the Fe(110)-graphene interface acts as a strong sink that traps defects,suggesting the potential usage of steel-graphene with multiply interface structures for tolerating the radiation damage.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 11174359 and 10874232)by the National Basic Research Program of China (Grant No. 2012CB932302)
文摘Double perovskite Bi2 FeCrO6 , related with multiferroic BiFeO3 , is very interesting because of its strong ferroelectricity and high magnetic Curie temperature beyond room temperature. We investigate its electronic structure and magnetic and optical properties by using a full-potential density-functional method. Our optimization shows that it is a robust ferrimagnetic semiconductor. This nonmetallic phase is formed due to crystal field splitting and spin exchange splitting, in contrast to previous studies. Spin exchange constants and optical properties are calculated. Our Monte Carlo magnetic Curie temperature is 450 K, much higher than any previously calculated value and consistent with experimental results. Our study and analysis reveal that the main magnetic mechanism is an antiferromagnetic superexchange between Fe and Cr over the intermediate O atom. These results are useful in understanding such perovskite materials and exploring their potential applications.
基金Project supported by the Youth Science and Technology Talent Project of Hunan Province of China (Grant No.2022RC1197)the National Natural Science Foundation of China (Grant No.52372260)。
文摘Grasping the underlying mechanisms behind the low lattice thermal conductivity of materials is essential for the efficient design and development of high-performance thermoelectric materials and thermal barrier coating materials.In this paper,we present a first-principles calculations of the phonon transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers.Both materials possess low lattice thermal conductivity,at least two orders of magnitude lower than graphene and h-BN.The room temperature thermal conductivity of Pb_(2)SbAs(0.91 W/m K)is only a quarter of that of Pb_(2)PAs(3.88 W/m K).We analyze in depth the bonding,lattice dynamics,and phonon mode level information of these materials.Ultimately,it is determined that the synergistic effect of low group velocity due to weak bonding and strong phonon anharmonicity is the fundamental cause of the intrinsic low thermal conductivity in these Janus structures.Relative regular residual analysis further indicates that the four-phonon processes are limited in Pb_(2)PAs and Pb_(2)SbAs,and the three-phonon scattering is sufficient to describe their anharmonicity.In this study,the thermal transport properties of Janus Pb_(2)PAs and Pb_(2)SbAs monolayers are illuminated based on fundamental physical mechanisms,and the low lattice thermal conductivity endows them with the potential applications in the field of thermal barriers and thermoelectrics.
基金Project supported by the Natural Science Foundation of WIUCAS (Grant Nos.WIUCASQD2023004 and WIUCASQD2022025)the National Natural Science Foundation of China (Grant Nos.12304006,12104452,12022508,12074394,and 12374061)+1 种基金the Shanghai Science and Technology Innovation Action Plan (Grant No.23JC1401400)the Natural Science Foundation of Wenzhou (Grant No.L2023005)。
文摘Titanium dioxide(TiO_(2))has attracted considerable research attentions for its promising applications in solar cells and photocatalytic devices.However,the intrinsic challenge lies in the relatively low energy conversion efficiency of TiO_(2),primarily attributed to the substantial band gaps(exceeding 3.0 eV)associated with its rutile and anatase phases.Leveraging multi-objective global optimization,we have identified two quasi-layered ternary Ti-O-S crystals,composed of titanium,oxygen,and sulfur.The calculations of formation energy,phonon dispersions,and thermal stability confirm the chemical,dynamical and thermal stability of these newly discovered phases.Employing the state-of-art hybrid density functional approach and many-body perturbation theory(quasiparticle GW approach and Bethe-Salpeter equation),we calculate the optical properties of both the TiOS phases.Significantly,both phases show favorable photocatalytic characteristics,featuring band gaps suitable for visible optical absorption and appropriate band alignments with water for effective charge carrier separation.Therefore,ternary compound TiOS holds the potential for achieving high-efficiency photochemical conversion,showing our multi-objective global optimization provides a new approach for novel environmental and energy materials design with multicomponent compounds.
基金financially supported by the New Energy Project for Electric Vehicle of National Key Research and Development Program (2016YFB0100200)the National Natural Science Foundation of China (51671004,U1764255)+1 种基金National Postdoctoral Program for Innovative Talents (BX201700001)supported by High-performance Computing Platform of Peking University
文摘To design the high-energy-density Li-ion batteries, the anode materials with high specific capacity haveattracted much attention. In this work, we adopt the first principles calculations to investigate the pos-sibility of a new two dimensional boron material, named Be, as anode material for Li-ion batteries. Thecalculated results show that the maximum theoretical specific capacity of Bc is 1653mAh g-1 （LiBl.s）.Additionally, the energy barriers of Li ion and Li vacancy diffusion are 330 meV and 110 meV, respec-tively, which imply fast charge and discharge ability for B6 as an anode material. The theoretical findingsreported in this work suggest that BG is a potential candidate as anode material of high-energy-density Li-ion batteries.
基金Project supported by Special Fund for Introduced Talent to Initiate Scientific Research in Nanjing Tech Universitythe National Natural Science Foundation of China (Grant Nos. 51831003 and 51771225)
文摘The lattice dynamics,elastic properties and the origin of vanished magnetism in equiatomic quaternary Heusler compounds CoMnVZ(Z=Al,Ga)are investigated by first principle calculations in this work.Due to the similar constituent atoms in CoMnVAl and CoMnVGa compounds,they are both stable in LiMgPdSn-type structure with comparable lattice size,phonon dispersions and electronic structures.Comparatively,we find that CoMnVAl is more structurally stable than CoMnVGa.Meanwhile,the increased covalent bonding component in CoMnVAl enhances its mechanical strength and Vickers hardness,which leads to better comprehensive mechanical properties than those of CoMnVGa.Practically and importantly,structural and chemical compatibilities at the interface make non-magnetic semiconductor CoMnVAl and magnetic topological semimetals Co2MnAl/Ga more suitable to be grown in heterostructures.Owing to atomic preferential occupation in CoMnVAl/Ga,the localized atoms Mn occupy C(0.5,0.5,0.5)Wyckoff site rather than B(0.25,0.25,0.25)and D(0.75,0.75,0.75)Wyckoff sites in LiMgPdSn-type structure,which results in symmetric band filling and consequently drives them to be non-magnetic.Correspondingly,by tuning localized atoms Mn to occupy B(0.25,0.25,0.25)or/and D(0.75,0.75,0.75)Wyckoff sites in off-stoichiometric Co-Mn-V-Al/Ga compounds and keeping the total valence electrons as 24,newly compensated ferrimagnetic compounds are theoretically achieved.We hope that our work will provide more choices for spintronic applications.
基金Project supported by the National Basic Research Program of China(Grant No.2011CBA00602)the National Science and Technology Major Project of the Ministry of Science and Technology of China(Grant No.2011ZX02708-002)
文摘Various biaxial compressive strained GaSb p-channel metal-oxide-semiconductor field-effect transistors （MOSFETs） are experimentally and theoretically investigated, The biaxial compressive strained GaSb MOSFETs show a high peak mobility of 638 cm2/V.s, which is 3.86 times of the extracted mobility of the fabricated GaSb MOSFETs without strain. Meanwhile, first principles calculations show that the hole effective mass of GaSb depends on the biaxial compressive strain. The biaxiai compressive strain brings a remarkable enhancement of the hole mobility caused by a significant reduction in the hole effective mass due to the modulation of the valence bands.
文摘The structural, electronic, and elastic properties of ZnSe1-xSx for the zinc blende structures have been studied by using the density functional theory. The calculations were performed using the plane wave pseudopotential method, as implemented in Quantum ESPRESSO. The exchange-correlation potential is treated with the local density approximation pz-LDA for these properties. Moreover, LDA＋U approximation is employed to treat the ＂d＂ orbital electrons properly. A comparative study of the band gap calculated within both LDA and LDA＋U schemes is presented. The analysis of results show considerable improvement in the calculation of band gap. The inclusion of compositional disorder increases the values of all elastic constants. In this study, it is found that elastic constants C11, C12, and C44 are mainly influenced by the compositional disorder. The obtained results are in good agreement with literature.
文摘In the paper, density of states, band structure and electron density difference of Zn1-xCdxO are calculated by first principles, here x varies from 0 to 0.75 at intervals of 0.125, and the band gap obtained from band structure changes from 0.968 eV to 0.043 eV. The lattice strain and p-d repulsion theory are used to investigate variation of the band gap, the results obtained show that the variation is mainly due to the lattice tensile strain. The p-d repulsion in Zn1-xCdxO cannot be neglected. In addition, electron density difference can be used to verify the results.
