First principles calculation of intermetallic compounds in FeTiCoNiVCrMnCuAl system high entropy alloy

The structural, electronic and elastic properties of common intermetallic compounds in FeTiCoNiVCrMnCuAI system high entropy alloy were investigated by the first principles calculation. The calculation results of formation enthalpy and cohesive energy show that FeTi, Fe2Ti, AlCrFe2, Co2Ti, AlMn2V and Mn2Ti phases may form in the formation process of the alloy. Further studies show that FeTi, FezTi, AlCrFe2, Co2Ti and AlMn2V phases with higher shear modulus and elastic modulus would be excellent strengthening phases in high entropy alloy and would improve the hardness of the alloy. In addition, the partial density of states was investigated for revealing the bonding mode, and the analyses on the strength of p-d hybridization also reveal the underlying mechanism for the elastic properties of these compounds.

First-principles Study on the Electronic Structure of Novel Titanium Yttrium Mixed-metal Nitride Clusterfullerene

We present a first-principles study on the geometric, vibrational and electronic properties of a novel Y-based non-scandium mixed-metal nitride clusterfullerene （TiY2N@C80）. Theoretical results indicate that the fundamental electronic properties of TiY2N@C80 are similar to that of TiSc2N@C80, but dramatically different from that of ScaN@C800 and YaN@C80 molecules. We find that the magnetism of TiY2N@C80 is quenched by carrier doping. The rotation energy barrier of the TiY2N cluster in C80 cage was obviously increased by exohedral chemical modification with pyrrolidine monoadduct.

First Principles Investigation of Electronic Property and High Pressure Phase Stability of SrnN

An investigation of electronic property and high pressure phase stability of SmN has been conducted using first principles calculations based on density functional theory. The elec- tronic properties of Stun show a striking feature of a half metal, the majority-spin electrons are metallic and the minority-spin electrons are semiconducting. It was found that Stun undergoes a pressure-induced phase transition from NaCl-type （B1） to CsCl-type structure （B2） at 117 GPa. The elastic constants of Stun satisfy Born conditions at ambient pressure, indicating that B1 phase of SmN is mechanically stable at 0 GPa. The result of phonon spectra shows that B1 structure is dynamically stable at ambient pressure, which agrees with the conclusion derived from the elastic constants.

Structural,phonon,elastic,thermodynamic and electronic properties of Mg-X(X=La,Nd,Sm)intermetallics:The first principles study

We show the results of first-principles calculations of structural,phonon,elastic,thermal and electronic properties of the Mg-X inter-metallics in their respective ground state phase and meta-stable phases at equilibrium geometry and the studied pressure range.Phonon dispersion spectra for these compounds were investigated by using the linear response technique.The phonon spectra do not show any abnormality in their respective ground state phase.The respective ground states phases of the studied system remain stable within the studied pressure range.Electronic and thermodynamic properties were derived by analysis of the electronic structures and quasi-harmonic approximation.The mixed bonding character of the Mg-X intermetallics is revealed by Mg-X bonds,and it leads the metallic nature.Most of the contribution originated from X ions d like states at Fermi level compared to that of Mg ion in these intermetallics.In this work,we also predicted the melting temperature of these intermetallics and evaluated the Debye temperature by using elastic constants.

Electrocatalytic and photocatalytic performance of noble metal doped monolayer MoS2 in the hydrogen evolution reaction: A first principles study

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).

High-throughput identification of one-dimensional atomic wires and first principles calculations of their electronic states

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.

First-principles study on the mechanical properties and thermodynamic properties of Mo-Ta alloys

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.

Search for potential K ion battery cathodes by first principles

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.

First principles study of hafnium intercalation between graphene and Ir(111)substrate

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.

Band structure,Fermi surface,elastic,thermodynamic,and optical properties of AlZr3,AlCu3,and AlCu2Zr:First-principles study

The electronic properties（Fermi surface,band structure,and density of states（DOS）） of Al-based alloys AlM3（M=Zr and Cu） and AlCu2Zr are investigated using the first-principles pseudopotential plane wave method within the generalized gradient approximation（GGA）.The structural parameters and elastic constants are evaluated and compared with other available data.Also,the pressure dependences of mechanical properties of the compounds are studied.The temperature dependence of adiabatic bulk modulus,Debye temperature,specific heat,thermal expansion coefficient,entropy,and internal energy are all obtained for the first time through quasi-harmonic Debye model with phononic effects for T = 0 K-100 K.The parameters of optical properties（dielectric functions,refractive index,extinction coefficient,absorption spectrum,conductivity,energy-loss spectrum,and reflectivity） of the compounds are calculated and discussed for the first time.The reflectivities of the materials are quite high in the IR-visible-UV region up to ~ 15 eV,showing that they promise to be good coating materials to avoid solar heating.Some of the properties are also compared with those of the Al-based Ni3 Al compound.

First Principles Study of Atomic Adsorption on (111) and (100) Surfaces of Iridium

We have investigated the adsorption of nine different adatoms on the(111)and(100)surfaces of Iridium(Ir)using first principles density functional theory.The study explores surface functionalization of Ir which would provide important information for further study of its functionality in catalysis and other surface applications.The adsorption energy,stable geometry,density of states and magnetic moment are some of the physical quantities of our interest.The study reveals that the three-/four-fold hollow site is energetically the most favorable adsorption site on the(111)/(100)surface of Ir.The investigation on a wide range of coverages(from 0.04 to 1 monolayer)reveals the strong coverage dependence of adsorption energy of the adsorbate atoms.The adsorption energy is found to increase as the coverage increases,implying a repulsive interaction between the adsorbates.Strong hybridization between the adsorbates and the substrate electronic states is revealed to impact the adsorption,while the magnetic moment of the adsorbates is found to be suppressed.The Bader analysis reveals significant amount of charge transfers between the adsorbate atoms and the substrate.The binding of adsorbate atoms on the(100)surface is observed to be moderately stronger as compared to that on the(111)surface.

Adsorption of Ag on M-doped graphene:First principle calculations

Graphene is an ideal reinforcing phase for a high-performance composite filler,which is of great theoretical and practical significance for improving the wettability and reliability of the filler.However,the poor adsorption characteristics between graphene and the silver base filler significantly affect the application of graphene filler in the brazing field.It is a great challenge to improve the adsorption characteristics between a graphene and silver base filler.To solve this issue,the adsorption characteristic between graphene and silver was studied with first principle calculation.The effects of Ga,Mo,and W on the adsorption properties of graphene were explored.There are three possible adsorbed sites,the hollow site(H),the bridge site(B),and the top site(T).Based on this research,the top site is the most preferentially adsorbed site for Ag atoms,and there is a strong interaction between graphene and Ag atoms.Metal element doping enhances local hybridization between C or metal atoms and Ag.Furthermore,compared with other doped structures(Ga and Mo),W atom doping is the most stable adsorption structure and can also improve effective adsorption characteristic performance between graphene and Ag.

First principle study of LiXS_2(X=Ga, In) as cathode materials for Li ion batteries

From first principle calculations, we demonstrate that LiXS_2（X = Ga, In） compounds have potential applications as cathode materials for Li ion batteries. It is shown that Li can be extracted from the LiXS_2 lattice with relatively small volume change and the XS_4 tetrahedron structure framework remains stable upon delithiation. The theoretical capacity and average intercalation potential of the LiGaS_2（LiInS_2） cathode are 190.4（144._2） m Ah/g and 3.50 V（3.53 V）. The electronic structures of the LiXS_2 are insulating with band gaps of _2.88 eV and 1.99 eV for X = Ga and In, respectively.However, Li vacancies, which are formed through delithiation, change the electronic structure substantially from insulating to metallic structure, indicating that the electrical conductivities of the LiXS_2 compounds should be good during cycling.Li ion migration energy barriers are also calculated, and the results show that Li ion diffusions in the LiXS_2 compounds can be as good as those in the currently widely used electrode materials.

Effects of Doping on Magnetic Properties of YCo_(5-x)Fe_x and YCo_(5-x) Ag_x——First Principles Calculation

One way of improving the magnetic properties of RECo5(RE = rare earth) compounds, especially the magnetic anisotropy energy (MAE), is to dope them with some additives such as Fe, Ni, Cu. Those dopants bring changes in both lattice geometry and magnetic properties of the compounds. In this paper, the effects of doping on YCo5-x,Fex and YCo5-x Agx were studied in two simple but effective ways: first, the geometric effect induced by doping and then, the pure doping role namely without any geometric changes. The calculated results indicate that the magnetic moments of Co show a transition from a high spin state to a low one with the change of the volume of the cell in all YCo5, YCo3Fe2 and YCo3Ag2 alloys. The change of c/a ratio with constant lattice parameter a also influences drastically the magnetic moments and the MAE. As the geometric structure is not changed, it is found that the doping effects of magnetic element Fe and non-magnetic element Ag are quite different.

Band structure of silicon and germanium thin films based on first principles

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.

First-principles investigation on structural and electrochemical properties of NaCoO_2 for rechargeable Na-ion batteries

NaxCoO2 is a commonly used cathode material for sodium ion batteries because of its easy synthesis, high reversible capacity and good cyclability. The structural and electrochemical properties of NaxCoO2 during sodium ion insertion/extraction process are studied based on first principles calculations. The calculation results of crystal structure parameters and average intercalation voltage are in good agreement with experiment data. Through calculation of the geometric structure and charge transfer in charging and discharging processes of NaxCoO2, it is found that the oxygen atom surrounding Co of the CoO6 octahedral screens the coulomb potential produced by sodium vacancy in NaxCoO2, and the charge is removed from the entire Co-O layer instead of the Co atom adjacent to sodium vacancy when sodium ions are extracted from the Na CoO2 lattice. Thus, during the insertion/extraction of sodium ion from Na CoO2, the CoO6 octahedral structure undergoes small lattice distortion, which makes the local structure quite stable and is beneficial to the cycling stability of the material for the application of sodium ion batteries.

First principles calculation on electronic structure,chemical bonding,elastic and optical properties of novel tungsten triboride

The electronic structures,chemical bonding,elastic and optical properties of the novel hP24 phase WB3 were investigated by using density-functional theory(DFT) within generalized gradient approximation(GGA).The calculated energy band structures show that the hP24 phase WB3 is metallic material.The density of state(DOS) and the partial density of state(PDOS) calculations show that the DOS near the Fermi level is mainly from the W 5d and B 2p states.Population analysis suggests that the chemical bonding in hP24-WB3 has predominantly covalent characteristics with mixed covalent-ionic characteristics.Basic physical properties,such as lattice constant,bulk modulus,shear modulus and elastic constants Cij were calculated.The elastic modulus E and Poisson ratio υ were also predicted.The results show that hP24-WB3 phase is mechanically stable and behaves in a brittle manner.Detailed analysis of all optical functions reveals that WB3 is a better dielectric material,and reflectivity spectra show that WB3 can be promised as good coating material in the energy regions of 8.5-11.4 eV and 14.5-15.5 eV.

First principles study of behavior of helium at Fe(110)-graphene interface

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.

First-principles study of magnetism of 3d transition metals and nitrogen co-doped monolayer MoS2

The electronic structures and magnetic properties of diverse transition metal (TM=Fe, Co, and Ni) and nitrogen (N) co-doped monolayer MoS2 are investigated by using density functional theory. The results show that the intrinsic MoS2 does not have magnetism initially, but doped with TM (TM=Fe, Co, and Ni) the MoS2 possesses an obvious magnetism distinctly. The magnetic moment mainly comes from unpaired Mo:4d orbitals and the d orbitals of the dopants, as well as the S:3p states. However, the doping system exhibits certain half-metallic properties, so we select N atoms in the V family as a dopant to adjust its half-metal characteristics. The results show that the (Fe, N) co-doped MoS2 can be a satisfactory material for applications in spintronic devices. On this basis, the most stable geometry of the (2Fe-N) co-doped MoS2 system is determined by considering the different configurations of the positions of the two Fe atoms. It is found that the ferromagnetic mechanism of the (2Fe-N) co-doped MoS2 system is caused by the bond spin polarization mechanism of the Fe-Mo-Fe coupling chain. Our results verify that the (Fe, N) co-doped single-layer MoS2 has the conditions required to become a dilute magnetic semiconductor.

Anisotropic elastic properties and ideal uniaxial compressive strength of TiB_2 from first principles calculations

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.