Papers by Keyword: First Principle

Abstract: The development of next generation Li ion battery has attracted many attentions of researchers due to the rapidly increasing demands to portable energy storage devices. General Li metal/alloy anodes are confronted with challenges of dendritic crystal formation and slow charge/discharge rate. Recently, the prosperity of two-dimensional materials opens a new window for the design of battery anode. In the present study, MoS₂/graphene heterostructure is investigate for the anode application of Li ion battery using first-principles calculations. The Li binding energy, open-circuit voltage, and electronic band structures are acquired for various Li concentrations. We found the open-circuit voltage decreases from ~2.28 to ~0.4 V for concentration from 0 to 1. Density of states show the electrical conductivity of the intercalated heterostructures can be significantly enhanced. The charge density differences are used to explain the variations of voltage and density of states. Last, ~0.43 eV diffusion energy barrier of Li implies the possible fast charge/discharge rate. Our study indicate MoS₂/graphene heterostructure is promising material as Li ion battery anode.

Abstract: The first-principles calculations by CASTEP program based on the density functional theory is applied to calculate the cohesive energy, enthalpy of formation, elastic constant, density of states and Mulliken population of Ag₃Sn、AgZn₃ and Ag₅Zn₈. Furthermore, the elastic properties, bonding characteristics, and intrinsic connections of different phases are investigated. The results show that Ag₃Sn、AgZn₃ and Ag₅Zn₈ have stability structural, plasticity characteristics and different degrees of elastic anisotropy; Ag₃Sn is the most stable structural, has the strongest alloying ability and the best plasticity. AgZn₃ is the most unstable structure, has the worst plasticity; The strength of Ag₅Zn₈ is strongest, AgZn₃ has the weakest strength, the largest shear resistance, and the highest hardness. Ag₅Zn₈ has the maximum Anisotropy index and Ag₃Sn has the minimum Anisotropy index. Ag₃Sn、AgZn₃ and Ag₅Zn₈ are all have covalent bonds and ionic bonds, the ionic bonds decrease in the order Ag₃Sn>Ag₅Zn₈>AgZn₃ and covalent bonds decreases in the order Ag₅Zn₈>Ag₃Sn>AgZn₃.

Abstract: In this work, we use first principles DFT calculations, anharmonic phonon scatter theory and Boltzmann transport method, to predict a comprehensive study on the thermoelectric properties as electronic and phonon transport of layered LaSe₂ crystal. The flat-and-dispersive type band structure of LaSe₂ crystal offers a high power factor. In the other hand, low lattice thermal conductivity is revealed in LaSe₂ semiconductor, combined with its high power factor, the LaSe₂ crystal is considered a promising thermoelectric material. It is demonstrated that p-type LaSe₂ could be optimized to exhibit outstanding thermoelectric performance with a maximum ZT value of 1.41 at 1100K. Explored by density functional theory calculations, the high ZT value is due to its high Seebeck coefficient S, high electrical conductivity, and low lattice thermal conductivity .

Abstract: The structural, mechanical, and thermodynamic properties of refractory metals Rh, Ir, W, Ta, Nb, Mo, Re, and Os have been systematically investigated by first-principles calculations based on density functional theory. Comparative studies reveal that Young's modulus (E = 636.42 GPa), shear modulus (G = 256.81 GPa), bulk modulus (B = 406.55 GPa), and microhardness (H = 44.69 GPa) of hexagonal Os are the highest, which reveals Os has the best overall mechanical properties. The body-centered cubic Nb has the smallest Young's modulus (E = 94.76 GPa), shear modulus (G = 33.62 GPa), bulk modulus (B = 174.50 GPa), and hardness (H = 2.04 GPa). Based on the ratio of bulk to shear modulus, it is judged that Rh, Ir, and Os are brittle materials (B/G < 1.75), and Nb, Ta, Mo, W, and Re exhibit ductile (B/G > 1.75). The elastic anisotropy has also been discussed by plotting both the 3D contours and the 2D planar projections of Young's modulus. For the face-centered cubic metals Rh and Ir and hexagonal close-packed metals Re and Os, the 3D contours of the Young's modulus are very similar, whereas body-centered cubic metals Ta, W, Nb, and Mo exhibit significant difference in elastic anisotropy. The thermodynamic calculations show that Debye temperature and minimum thermal conductivity decreases along Rh, Os, Mo, Ir, Re, W, Ta, Nb sequence. Furthermore, the results can be used as a general guidance for the design and development of high temperature refractory alloy system.

Abstract: Germanene, which has the same structure as graphene, is an exciting novel 2D functionalized material that controls its band gap using functionalization. The effects of the Ga atom and hydrogen atoms on the structure of Ga-doped H-passivated germanene were investigated with a density functional theory (DFT) calculation. H-passivated germanene has a direct gap of 2.10 eV. Opening the band gap in the H-passivated germanene is due to transition from sp² to sp³ orbital. Adsorption of the Ga adatom on H-site decrease the band gap to 1.38 eV. No interaction between Ga atoms and Hydrogen atoms was observed. Hence, their effects on the band structure of hydrogenated graphene were independent of each other. Our results suggest that hydrogen passivation combined with adsorption of the Ga adatoms could effectively control the band gap of germanene.

Abstract: The structural, mechanical, and thermodynamic properties of platinum group metals (Pt, Pd, and Ru) were systematically investigated by first-principles calculations based on density functional theory. Comparative studies show that Ru has the best comprehensive mechanical properties. Based on the Pugh’s rule and Poisson’s ratio, it is judged that Pt and Pd are ductility materials, and Ru exhibits obvious brittleness. Furthermore, the elastic anisotropy is also discussed by plotting both the 3D contours and the 2D planar projections of Young's modulus and shear modulus. The predicted elastic anisotropy factors indicate that the degree of elastic anisotropy of Pd is significant, while Ru has the smallest elastic anisotropy. By using the Clarke’s model, the minimum thermal conductivities of these metals have also been analyzed, and the results indicate that the low minimum thermal conductivity is proportional to the Debye temperature Θ_D. The above results can provide a valuable reference for revealing the microscopic deformation mechanism and designing new materials.

Abstract: In this paper, the electronic structure in armchair graphene nanoribbons (AGNRs) and graphene nanoribbons doped B at the edge (B-AGNRs) are obtained based on the first principle theory. It shows that the band gap has the oscillation characteristic whose period is 3. The band gap oscillating characteristic gradually vanishes and tends to be stable after doping B at graphene nanoribbons edge. This provides a theoretical guidance for developing the stable graphene nanodevices.

Abstract: The electronic structure and optical properties of GaP were calculated using generalized gradients in density functional theory. The Bonn effective charge, optical frequency dielectric constant and the LO-TO splitting value were calculated by density functional theory perturbation method.

Abstract: According to first-principle based on the density functional theory, the magnetic and optical properties of single layer CrSi₂ are calculated and analyzed by plane wave pseudo potential method. The band structure, density of state, optical absorption spectra, reflectivity and energy loss function of single layer CrSi₂ are obtained. The results show that single layer CrSi₂ has the properties of metal and magnetism. The calculations of optical properties of single layer CrSi₂ material deduce that it can absorb photons which belong to visible to ultraviolet region, even in far-infrared and far-ultraviolet regions. Single layer CrSi₂ has a good optical permeability to photon (with energy from 13 to 40eV), which shows that single layer CrSi₂ is suitable for optoelectronic devices, especially in infrared and vacuum ultraviolet detection applications.

Abstract: To investigate the deformation behavior of Mg-X(X=Zn, Y) binary solid solution, the strain-stress curve of crystal cell along [0001] for Mg-1.85at.%X(X=Zn, Y) alloy were simulated using first-principles calculations in this study. The simulation presents directly the critical resolved shear stress for pyramidal plane slip systems for Mg-1.85at.%X(X=Zn, Y) alloy. The results show that the minimum critical resolved shear stress (CRSS) of Mg, Mg-1.85at. %Zn and Mg-1.85at. %Y for pyramidal plane slip systems is 2.24, 2.72, 2.96 GPa respectively.