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.

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.

Hydrogen Incorporation in Crystalline Jadeite: Insight from First Principles Calculations

Hydrogen incorporation is critical for explaining defect energies, structure parameters and other physical characteristics of minerals and understanding mantle dynamics. This work analyzed the hydrogen complex defects in jadeite by the plane-wave pseudo-potential method based on density functional theory, and optimized the atomic positions and lattice constants in all configurations （different defective systems）. Incorporation mechanisms considered for hydrogen （H） in jadeite include： （1） hydrogen incorporating with the 02 site oxygen and coexisting with M2 vacancy; （2） one H atom combined with an AI atom replacing Si in tetrahedron; （3） 4H atoms directly replacing Si in tetrahedron and （4） 3H atoms replacing Al on the M1 site. The four incorporation mechanisms mentioned above form the corresponding VNa-Hi, Alsi-Hi, Vsi-4Hi and VAr3Hi point defects. The molecular dynamics simulation to the ideal, VNa-Hi, Alsi-Hi, Vsi-4Hi and VAr3Hi point defects under the P-T conditions of 900 K, 2 GPa, the Vsa-Hi and Alsi-Hi point defects under different pressures at T = 900 K, and Alsj-Hj point defects under different temperatures at P = 3 GPa was performed to examine the preferential mode of hydrogen incorporation in jadeite by means of first-principles calculations. The calculations show that the averaged O-H bond-length in the hydrogen point defects system decreased in the order of Alsi-Hi, VNa-HI, Vsl-4Hf and VAI-3Hi. VNa-HI complex defects result in a contraction of the jadeite volume and the presence of Alsi-Hi, Vsi-4H~ and VAI-3Hi defects could increase the superceli volume, which is the most obvious in the VAt-3Hi defects. The energy of formation of Also-HI and VA[-3HI complex defects was much lower than that of other defect systems. The VAI-3Hi defects system has the lowest energy and the shortest O-H bond-length, suggesting that this system is the most favorable. The analytical results of vacancy formation energy, O-H bond- length, and the stability of the hydrogen defects in jadeite have suggested that the preferred hydration incorporation mode in jadeite is VAI-3Hi complex defect.

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.

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.

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.

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.

First-principles calculations of structural, electronic, and thermodynamic properties of ZnO_(1-x)S_x alloys

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.

MgO-decorated carbon nanotubes for CO_2 adsorption:first principles calculations

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.

Electronic Structure and Optical Properties in Uranium Dioxide:the First Principle Calculations

We report a study of the electronic structure and optical properties of uranium dioxide （U02） based on the ab-initio density-functional theory and using the generalized gradient approximation. To correctly describe the strong correlation between 5 f electrons of a uranium atom, we employ the on-site Hubbard U correction term and optimize the correlation parameter of the bulk uranium dioxide. Then we give the structural and electronic properties of the ground state of uranium dioxide. Based on the accurate electronic structure, we calculate the complex dielectric function of UO2 and the related optieM properties, such as reflectivity, refractive index, extinction index, energy loss spectra, and absorption coefficient.

First principles calculations on the thermoelectric properties of bulk Au2S with ultra-low lattice thermal conductivity

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.

Magnetic and Electronic Properties of Double Perovskite Ba2SmNbO6 without Octahedral Tilting by First Principle Calculations

The structural, magnetic and electronic properties of the double perovskite Ba2SmNbO6 （for the simple cubic structure where no octahedral tilting exists anymore） are studied using the density functional theory within the generalized gradient approximation as well as taking into account the on-site Coulomb repulsive interaction. The total energy, the spin magnetic moment, the band structure and the density of states are calculated. The optimization of the lattice constants is 8.5173 A, which is in good agreement with the experimental value 8.5180 A. The calculations reveal that Ba2SmNbO6 has a stable ferromagnetic ground state and the spin magnetic moment per molecule is 5.00μB/f.u. which comes mostly from the Sin3＋ ion only. By analysis of the band structure, the compound exhibits the direct band gap material and half-metallic ferromagnetic nature with 100% spin-up polarization, which implies potential applications of this new lanthanide compound in magneto-electronic and spintronic devices.

A Calorimetric Study Assisted with First Principle Calculations of Specific Heat for Si-Ge Alloys within a Broad Temperature Range

Calorimetric measurements are performed to determine the specific heat of Si-xat.% Ge(where x = 0, 10, 30,50, 70, 90 and 100) alloys within a broad temperature range from 123 to 823 K. The measured specific heat increases dramatically at low temperatures, and the composition dependence of specific heat is evaluated from the experimental results. Meanwhile, the specific heat at constant volume, the thermal expansion, and the bulk modulus of Si and Ge are investigated by the first principle calculations combined with the quasiharmonic approximation. The negative thermal expansion is observed for both Si and Ge. Furthermore, the isobaric specific heat of Si and Ge is calculated correspondingly from OK to their melting points, which is verified by the measured results and accounts for the temperature dependence in a still boarder range.

First Principles Calculation of Magnetic Resonance Properties of Cu_2-<i>δ</i>X (X = Se, S, Te)

In order to have a better understanding of the electronic structures and physical properties of Cu2-δX (X = Se, S, Te) copper chalcogenides. First principles were performed to calculate the chemical shift, band structure, and electron density of states of Cu2-δX (X = Se, S, Te). By comparing our calculation results with previous experimental works, we found that the predicted electronic structures of Cu2Se, Cu2Te and Cu2S transform from semimetal to semiconductor after adding on-site Coulomb U, which reflects the real properties of the materials. By using (Density Functional Theory) DFT + U method, the calculation result is close to the real electronic structure. The calculation result of chemical shift of adding U does not reach the ideal expectation, and the reason is not clear at present. In this paper, the theoretical electronic structures of Cu2Se, Cu2Te and Cu2S are better calculated by DFT + U method and compared with the actual properties. The effect of Cu-s electron on the chemical shift is understood, and a theoretical result of the chemical shift is calculated, which provides a powerful reference for the subsequent research and understanding of the electronic structure and physical properties of the compounds with S groups of Cu.

Theoretical calculations of structural, electronic, and elastic properties of CdSe_(1-x)Te_x:A first principles study

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.

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).

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.