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.

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.

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.

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.

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 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.

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.

Effects of external stress aging on morphology and precipitation behavior of θ'' phase in Al-Cu alloy

The exposure of Al-5Cu alloy to an external stress with normal aging was carried out. The effects of external stress-aging on the morphology and precipitation behavior of θ＂ phase were investigated by transmission electron microscopy （TEM）, differential scanning calorimetry （DSC） and first principle calculation. The size of the θ＂ phase precipitated plates in stress-aging （453 K, 6 h, 50 MPa） is 19.83 nm, which is smaller than that of those present （28.79 nm） in stress-flee aging （453 K, 6 h）. The precipitation process of θ＂ phase is accelerated by loading external stress aging according to the analysis of DSC results. The apparent activation energy for the external stress-aging is 10% lower than the stress-free one. The first principle calculation results show that the external stress makes a decrease of 6% in the interface energy. The effects of the stress on aging process of the alloy are discussed on the basis of the classical theory. The external stress changes the morphology and precipitation behavior of θ＂ phase because the critical nucleation energy is decreased by 19% under stress aging.

Extensive Computational Study on Conformations of Microsolvated Leucine Complexes

The conformations for leucine （Leu） hydrated with one to three water molecules, Leu-（H2O）n （n=1-3）, were carefully searched by considering the trial structures generated by all possible combinations of rotamers of Leu combined with all likely hydration modes. The structures were optimized at the BHandHLYP/6-31＋G^＊ level and the single point energies were calculated at the BHandHLYP/6-311＋＋G^＊＊ level. Good correspondence between the conformations of Leu-（H2O）n and bare Leu is found, showing that the conformations of Leu-（H2O）n may be efficiently and reliably determined by the hydration of Leu conformers. The simulated IR spectra of canonical and zwitterionic conformers of Leu-（H2O）n are compared with the experimental result of Leu in aqueous solution. The IR spectrum of zwitterionic Leu- （H2O）3 provides the best description of the experiment. The result demonstrates that the IR spectrum of solute in solution may be simulated by the solute hydrated with an adequate number of water molecules in the gas phase.

Approaching High-Performance Lithium Storage Materials by Constructing Hierarchical CoNiO_(2)@CeO_(2)Nanosheets

In this work,the hierarchical CoNiO_(2)@CeO_(2)nanosheet composites were successfully prepared by a one-step hydrothermal process with a subsequent annealing process for the first time.The CeO_(2)nanoparticles successfully deposit on the surface of CoNiO_(2)nanosheet,and benefit the improvement of electrical contact between CoNiO_(2)and CeO_(2).CeO_(2)modification improve the reversibility of insertion/extraction of Li-ions and electrochemical reaction activity,and promotes the transport of Li-ions.Benefited of the unique architecture and component,the CoNiO_(2)@CeO_(2)nanosheet composites show high-reversible capacities,excellent cycling stability and good rate capability.The CoNiO_(2)@CeO_(2)(5.0 wt%)shows a charge/discharge capacity of 867.1/843.2 m Ah g^(-1)after 600 cycles at 1 A g^(-1),but the pristine CoNiO_(2)@CeO_(2)nanosheet only delivers a charge/discharge capacity of 516.9/517.6 m Ah g^(-1)after 500 cycles.The first-principles calculation reveals that valid interfaces between CeO_(2)and NiCoO_(2)can be formed,and the formation process of the interfaces is exothermic.The strong interfacial interaction resulting in an excellent structure stability and thus a cycling stability of the CoNiO_(2)@CeO_(2)material.This work provides an effective strategy to develop highperformance anode materials for advanced a lithium-ion battery,and the CoNiO_(2)@CeO_(2)nanosheet shows a sizeable potential as an anode material for next generation of high-energy Li-ion batteries.

High CO_(2) absorption capacity of metal-based ionic liquids: A molecular dynamics study

The absorption of CO_(2)is of importance in carbon capture,utilization,and storage technology for greenhouse gas control.In the present work,we clarified the mechanism of how metal-based ionic liquids (MBILs),Bmim[XCl_(n)]_(m)(X is the metal atom),enhance the CO_(2)absorption capacity of ILs via performing molecular dynamics simulations.The sparse hydrogen bond interaction network constructed by CO_(2)and MBILs was identified through the radial distribution function and interaction energy of CO_(2)-ion pairs,which increase the absorption capacity of CO_(2)in MBILs.Then,the dynamical properties including residence time and self-diffusion coefficient confirmed that MBILs could also promote the diffusion process of CO_(2)in ILs.That's to say,the MBILs can enhance the CO_(2)absorption capacity and the diffusive ability simultaneously.Based on the analysis of structural,energetic and dynamical properties,the CO_(2)absorption capacity of MBILs increases in the order Cl^-→[ZnCl_(4)]^(2-)→[CuCl_(4)]^(2-)→[CrCl_(4)]^-→[FeCl_(4)]^-,revealing the fact that the short metal–Cl bond length and small anion volume could facilitate the performance of CO_(2)absorbing process.These findings show that the metal–Cl bond length and effective volume of the anion can be the effective factors to regulate the CO_(2)absorption process,which can also shed light on the rational molecular design of MBILs for CO_(2)capture and other key chemical engineering processes,such as IL-based gas sensors,nano-electrical devices and so on.

Surface,Size and Thermal Effects in Alkali Metal with Core-Electron Binding-Energy Shifts

Consistency between density functional theory calculations and X-ray photoelectron spectroscopy measurements confirms our predications on the undercoordination-induced local bond relaxation and core level shift of alkali metal,which determine the surface,size and thermal properties of materials.Zone-resolved photoelectron spectroscopyanalysis method and bond order-length-strength theory can be utilized to quantify the physical parameters regarding bonding identities and electronic property of metal surfaces,which allows for the study of the core-electron binding-energy shifts in alkali metals.By employing these methods and first principle calculation in this work,we can obtain the information of bond and atomic cohesive energy of under-coordinated atoms at the alkali metal surface.In addition,the effect of size and temperature towards the binding-energy in the surface region can be seen from the view point of Hamiltonian perturbation by atomic relaxation with atomic bonding.

Strain and interfacial engineering to accelerate hydrogen evolution reaction of two-dimensional phosphorus carbide

Hydrogen,regarded as a promising energy carrier to alleviate the current energy crisis,can be generated from hydrogen evolution reaction(HER),whereas its efficiency is impeded by the activity of catalysts.Herein,effective strategies,such as strain and interfacial engineering,are imposed to tune the catalysis performance of novel two-dimensional(2D)phosphorus carbide(PC)layers using first-principle calculations.The findings show that P site in pristine monolayer PC(ML-PC)exhibits higher HER performance than C site.Intriguingly,constructing bilayer PC sheet(BL-PC)can change the coordinate configuration of P atom to form 3-coordination-P atom(3-co-P)and 4-coordination-P atom(4-co-P),and the original activity of 3-co-P site is higher than the 4-co-P site.When an external compressive strain is applied,the activity of the 4-co-P site is enhanced whereas the external strain can barely affect that of 3-co-P site.Interestingly,the graphene substrate enhances the overall activity of the BL-PC because the graphene substrate optimizes the?GH*value of 4-co-P site,although it can barely affect the HER activity of 3-co-P site and ML-PC.The desirable properties render 2 D PC-based material promising candidates for HER catalysts and shed light on the wide utilization in electrocatalysis.

Theoretical investigation on radiation tolerance of M(n＋1)AXn phases

Ternary Mn＋1AXn phases with layered hexagonal structures, as candidate materials used for next-generation nuclear reactors, have shown great potential in tolerating radiation damage due to their unique combination of ceramic and metallic properties. However, Mn＋1AXn materials behave differently in amorphization when exposed to energetic neutron and ion irradiations in experiment. We first analyze the irradiation tolerances of different Mn＋1AXn（MAX） phases in terms of electronic structure, including the density of states（DOS） and charge density map. Then a new method based on the Bader analysis with the first-principle calculation is used to estimate the stabilities of MAX phases under irradiation. Our calculations show that the substitution of Cr/V/Ta/Nb by Ti and Si/Ge/Ga by Al can increase the ionicities of the bonds,thus strengthening the radiation tolerance. It is also shown that there is no obvious difference in radiation tolerance between Mn＋1ACn and Mn＋1ANn due to the similar charge transfer values of C and N atoms. In addition, the improved radiation tolerance from Ti3AlC2 to Ti2AlC （Ti3AlC2 and Ti2AlC have the same chemical elements）, can be understood in terms of the increased Al/TiC layer ratio. Criteria based on the quantified charge transfer can be further used to explore other Mn＋1AXn phases with respect to their radiation tolerance, playing a critical role in choosing appropriate MAX phases before they are subjected to irradiation in experimental test for future nuclear reactors.

Hollow sphere of heterojunction(NiCu)S/NC as advanced anode for sodium-ion battery

Metal sulfide is considered as a potential anode for sodium-ion batteries(SIBs),due to the high theoretical capacity,strong thermodynamic stability and low-cost.However,their cycle capacity and rate performance are limited by the excessive expansion rate and low intrinsic conductivity.Herein,heterogeneous hollow sphere NiS-Cu_(9)S_(5)/NC(labeled as(NiCu)S/NC)based on Oswald ripening mechanism was prepared through a simple and feasible methodology.From a structural perspective,the hollow structure provides an expansion buffer and raises the electrochemical active area.In terms of electron/ion during the cycles,Na^(+)storage mechanism is optimized by NiS/Cu_(9)S_(5)heterogeneous interface,which increases the storage sites and shortens the migration path of Na^(+).The formation of built-in electric field strengthens the electron/ion mobility.Based on the first principle calculations,it is further proved the formation of heterogeneous interfaces and the direction of electron flow.As the anode for SIBs,the synthesized(NiCu)S/NC delivers high reverse capacity(559.2 mA h g^(-1)at 0.5 A g^(-1)),outstanding rate performance(185.3 mA h g^(-1)at 15 A g^(-1)),long-durable stability(342.6 mA h g^(-1)at 4 A g^(-1)after 1500cycles,150.0 m A h g^(-1)at 10 A g^(-1)after 20,000 cycles with 0.0025%average attenuation rate).The matching cathode electrode Na_(3)V_(2)(PO_(4))_(3)/C is assembled with(NiCu)S/NC for the full-battery that achieves high energy density(253.7 W h kg^(-1))and reverse capacity(288.7 mA h g^(-1)).The present work provides a distinctive strategy for constructing electrodes with excellent capacity and stability for SIBs.

Stability and optoelectronic property of low-dimensional organic tin bromide perovskites

The toxicity and degradation of hybrid lead-halide perovskites hinder their extensive applications.It is thus of great importance to explore non-toxic alternative materials with excellent stability and optoelectronic property.We investigate the atomic structures and optoelectronic properties of non-toxic organic tin bromide perovskites(OTBP)with one/zerodimensional(1D/0D)structures by first-principles calculations.The calculated atomic structures show that the 1D/0D OTBPs are stable and the structure of inorganic octahedra in 0D is higher order than that in 1D.Moreover,the origination of exceptional purity emitting light in experiments is explained based on the calculated electronic structure.

Vibrational properties of cagelike diamondoid nitrogen at high pressure

Under high pressure, a cagelike diamondoid nitrogen structure was lately discovered by first-principles structure researches. This newly proposed structure is very unique and has not been observed in any other element. Using densityfunctional calculations, we study the pressure effect on its vibrational properties. The Born effective charges are calculated, and the resulting LO-TO splittings of certain infrared active modes are beyond 20 cm-1. We depict the F-point vibrational modes and find the breathing mode, rotational mode, and shearing mode. Frequencies of all the optical modes increase with pressure increasing. Moreover, the relation between the breathing mode frequency and the nitrogen cage diameter is discussed in detail. Our calculation results give a deeper insight into the vibrational properties of the cagelike diamondoid nitrogen.

Can HHe^(+)exist at high pressure:Exploration of high pressure induced HF–He compounds

HHe^(+)is considered as the strongest acid and most powerful proton donor known to human.Whether HHe^(+)exists at planetary high pressure environment is a quite important problem in physics,chemistry and planetary sciences.Here,using the ab initio evolutionary algorithm USPEX package,we searched HF–He system,which was reported as the most possible candidate to contain HHe^(+).The calculation proved HHe^(+)cannot form at pressure<1000 GPa,due to a conflict between the covalent component in symmetric hydrogen bond and ionic HHe^(+).Although He atoms have no chemical bonding with other elements,they can supply a chemical pressure,leading to two new phases He2(HF)4 and He(HF).With coplanar(HF)_(4)rings,He_(2)(HF)_(4)have an aromaticity-like electronic behavior while He(HF)has a new type of chiral HF chain.The formation of He_(2)(HF)_(4)and He(HF)prove that the chemical pressure from He,on par with external pressure,have ability to control the structural and electronic configuration and induce some new familiars of compounds include H and He elements which are fundamental planetary materials in giant planets.

Magnetic anisotropy in 5d transition metal-porphyrin molecules

Single molecule magnets(SMMs) with large magnetic anisotropy energy(MAE) have great potential applications in magnetic recording.Using the first-principles calculations,we investigate the MAE of 5 d transition metal-porphyrin-based SMMs by using the PBE and PBE+U with different U values,respectively.The results indicate that W-P,Re-P,Os-P,and Ir-P possess the considerably large MAE among 5 d TM-P SMMs.Furthermore,the MAE of 5 d TM-P can be facilely manipulated by tensile strain.The reduction of the absolute value of MAE for Ir-P molecule caused by tensile strain makes it easier to implement the writing operation.The decreasing of the occupation number of minority-spin channels of Ir-d_(x^(2)-y^(2)) orbital leads the MAE to decrease when the tensile strain increases.