First-principles Calculation Method Research Articles

Predicting mechanical properties of high entropy alloys with face centered cubic structure from first principles calculations

High-entropy alloys (HEAs) are a class of solid-solution alloys with multiple equal or nearly-equal molar constituents and found to exhibit excellent mechanical properties. In this study, we have developed the first-principles density functional theory based computational methods to predict the elastic constants and yield strength of the HEAs with face centered cubic (fcc) crystal structure. Moreover, the developed computational methods were applied to four fcc HEAs including CoFeNi, CoCrFeNi, CoCrFeCuNi, and RhIrPdPtNiCu with equal molar composition. Specifically, we predicted the Young’s modulus to be 204 GPa for CoFeNi, 226 GPa for CoCrFeNi, 217 GPa for CoCrFeCuNi, and 213 GPa for RhIrPdPtNiCu, and the yield strength to be 232 MPa for CoFeNi, 268 MPa for CoCrFeNi, 212 MPa for CoCrFeCuNi, and 520 MPa for RhIrPdPtNiCu. These computational predicted values are found to agree well with available experimental data. Therefore, these first-principles calculation methods can be used for expedite optimization on the mechanical properties of HEAs across vast composition space.

Rational design of intrinsic and defective BGe monolayer as the anode material for Li-ion batteries

The rational design of high-performance anode materials is an effective strategy to expedite the development of next-generation lithium-ion rechargeable batteries (LIBs). In this work, the first-principles calculation method is applied to systematically investigate the adsorption and diffusion behaviors of Li ions on the intrinsic and defective BGe monolayer, as well as the application prospects of such materials acting as anode materials for LIBs. Our results show that intrinsic planar BGe monolayer has the advantages of high structural stability, distinct metallic feature and strong interaction with Li. In addition, Li migration on the BGe surface shows a low diffusion barrier (0.32 ​eV), which could guarantee a rapid charging/discharging capability. Interestingly, the presence of the single B vacancy defect weakens the adsorption strength of Li ion in the defective regions due to the charge redistribution. Correspondingly, the defect slightly impedes the diffusion performance, resulting in an increased energy barrier for Li ion (0.44 ​eV) to escape the defective regions. On the other hand, the intrinsic BGe monolayer could be lithiated into BGeLi3 with a theoretical specific capacity of 1927 ​mA ​h ​g−1. The moderate open-circuit voltage and the flexible structural stability with negligible volume change further enhance the reversibility of BGe anode materials. All these results provide a robust foundation for the rational design of BGe monolayer as an efficient anode material for LIBs.

The elasticity, anisotropy and thermodynamic properties of binary and ternary B–Sc compounds: First-principles calculations

In the past few years, binary and ternary transition metal borides have attracted extensive attentions. Herein, we employed the first-principles calculations method to predict the structural properties, electronic, hardness, elastic and thermodynamic properties of binary and ternary Sc–B and Sc-X-B compounds. The calculated lattice parameters result of Sc–B and Sc-X-B compounds accord well with the available experimental results. The phonon frequencies and formation enthalpies display that all B–Sc type compounds are thermodynamically stable. Based on the criterion of mechanical stability, it can be concluded that Sc–B and Sc-X-B compounds have the mechanical stability. The analysis of band structure and state density displayed the metallic properties. ScB2 and ScB12 have the larger Young's modulus and ScB2 and ScB12 have the higher hardness. According to Poisson's ratio and the ratio for shear modulus and bulk modulus (G/B), it is proved that all Sc–B and Sc-X-B compounds are the ductile materials. Finally, the Debye temperature of B–Sc type compounds at high temperatures obeys the sequence of ScB12> ScB2> Sc3SnB > Sc3PbB > Sc3TlB > Sc3InB.

Effects of Zn, Mg and Cu Doping on Oxidation Reaction of Al (111) Surface

Aiming at the performance degradation of lithium-ion batteries due to shell corrosion, the doping of alloy elements Zn, Mg and Cu on Al (111) surface and the effect on oxidation reaction of Al (111) surface were studied by the first-principles calculation method. The results show that Zn, Mg and Cu atoms stably combine with Al atoms, and the surface smoothness is slightly different due to their different radii and electronegativity. The dissociative adsorption of O2 molecules is related to the surface doping atoms and O2 coverage, while the electron tunneling of underlying metal promotes O2 adsorption on the surface. As O2 coverage increases, the O atoms adsorbed on the hcp site gradually migrate to the subsurface layer. Zn, Mg, Cu and vacancy defect hinder the migration of the surrounding O atoms to subsurface layer, resulting in different structures and thicknesses of the oxide film near the doped atoms. At the same time, Zn, Mg, and Cu atoms differ in their ability to gain or lose electrons compared with Al atoms, resulting in their different positions on the surface. In addition, the surface work function rises with the increase of O2 coverage, and Zn and Cu atoms make the work function increase faster. Finally, according to the research results, it can be inferred that Zn and Mg are the unfavorable factors for the oxidation reaction of Al surface.

The surface alloying of aluminum with Sn and Pb for enhancement mechanism under high current pulsed electron beam

The purpose of this study is to investigate the solid solution strengthening (SSS) of Sn, Pb in aluminum (Al) matrix under high current pulses electron beam (HCPEB) irradiation. First-principles calculations method was adopted to quantify the effect of SSS with various concentrations. The capacity to strengthen is correlated with a nearly linear concentration dependency. In experimental section, the microstructures of the Pb/ and Sn/Al systems were characterized by SEM and TEM analysis. The solubility limit of both systems under HCPEB irradiation were calculated by a simple thermodynamic model. It is found that the Sn/Al system has a higher solid solubility, compared to that of the Pb/Al. In addition, the values of SSS of the Pb/ and Sn/Al systems were estimated. The results show that the Sn/Al system has higher strengthening ability than that of the Pb/Al system under HCPEB irradiation due to the different solid solubility, which is consistent with theory.

Metallic Penta-BN2 monolayer: A novel platform for non-lithium-ion batteries with high capacity and splendid cyclicity

Investigating high-capacity anode materials for non-lithium-ion batteries (NLIBs) would further enhance the possibility of the human being free from fossil energy. By applying the first-principles calculation method based on density functional theory, in this work, the scientific feasibility of employing penta-BN2 monolayer as anode material for NLIBs (Na, K, Mg, and Ca-ion batteries) is systematically investigated. The results show that the penta-BN2 exhibits excellent thermodynamic stability and superior electrical conductivity, and its intrinsic metallic property is maintained after ionization. Remarkably, the calculated theoretical specific capacities of penta-BN2 monolayer are 690.23, 690.23, 1380.45, and 1380.45 mAh·g−1 for Na+, K+, Mg2+, and Ca2+, respectively, which are outstanding among most of the previously proposed candidate anode materials for NLIBs. In addition, the moderate open-circuit voltages of penta-BN2 make itself suitable for anode applications. More importantly, the splendid reversibility of penta-BN2 contributes to extremely low diffusion energy barriers for metal ions. These results suggest that the penta-BN2 monolayer has a promising application prospect as anode for NLIBs with high energy density and outstanding rate performance.

Adsorption of residual gas on the (001) surface of Cs/O co-sensitized In0.53Ga0.47As photocathode

For near-infrared low-light image intensifiers, the low quantum efficiency of the photocathode is often a critical cause limiting its widespread use. Of these, the damage caused by residual gas molecules attached to the cathode surface during the sensitization process is most likely to be blamed. Herein, using the first-principles calculation method, we inspected the behavior of different gas molecules adhering on the sensitized In0.53Ga0.47As photocathode surface. Particular emphasis is placed on changes in surface stability and electronic properties. The detailed calculation results show that the adhering of gas molecules significantly destroy the original atomic stability of the cathode surface. In addition, a new dipole named [Cs-Gas] is formed, which greatly damages the surface electronic properties, especially increasing the surface work function and electron affinity. Besides, we also compared the diverse performances of residual gas molecules adsorption on two different systems (only-Cs and Cs/O sensitized surface). Our investigations are dedicated to further revealing the effect of residual gas molecules adsorption on the photoelectric properties of Cs/O co-sensitized In0.53Ga0.47As (001) surface.

First-principle study on the effects of hydrogen in combination with alloy solutes on local mechanical properties of steels

The first-principle calculation method has been utilized to study the effects of hydrogen in combination with alloy elements on the mechanical properties of iron-based super-cells, with the aim to bring new insight in the design of hydrogen-resistant steels. It is found that hydrogen prefers the second and third tetrahedral interstitial sites of the alloy solutes. Nb/Zr/Mo/W/Al alloyed super-cells dropped the most in the bulk modulus by hydrogen addition. Ni/Nb/Cu/Co/Zr dropped the most in the shear modulus/Young's modulus/hardness. The underlying influencing mechanisms on the elastic mechanical properties are discussed in perspective of atomic parameters/density of states/charge density/difference charge density/Bader charge analysis.

Formation and Performance of Diamond (111)/Cu Interface from First-Principles Calculation

The interface formation and properties of composite materials are very important for the preparation of composite materials, and the bonding state and charge transfer between atoms in the interface have a particularly significant effect on the interface formation. In this work, the first-principles calculation method was used to study the adsorption behavior and molecular dynamics of copper atoms on the (111) surface of H-terminated diamond, and the adsorption energy and adhesion work of Cu atoms were calculated. The results show that the adsorption of copper atoms is not sensitive to the diamond (111) surface, the adsorption work is very small at the four high symmetry positions, and the adhesion work is the largest at the T4 position and is 0.6106 J/m2. Furthermore, according to the electron localization function (ELF) analysis, there is no compound formation between Cu and H atoms; only a small amount of charge transfer exists, which belongs to physical adsorption. The diamond–copper interface formed by the growth of adsorption sites is a metastable structure without energy stability. This work provides an important theoretical reference for understanding the formation mechanism of copper-based diamond composites.

Theoretical probing the anchoring properties of BNP2 monolayer for lithium-sulfur batteries

Lithium-sulfur (Li-S) battery is blocked to implement as a practical energy storage device ascribes to the shuttle effect during charging and discharging processes. To solve the shuttle effect problem, one feasible method is to design a suitable anchoring material on the electrode. In this study, we explore the potential application of the BNP2 monolayer as an anchoring material through the first-principles calculation method. The results show that BNP2 with adequate adsorption energies (from 0.71 eV to 3.60 eV) can inhibit the shuttle effect without causing lithium polysulfides (LiPSs) decomposition. Then, by analyzing the projected density of states, it can be found that the property of BNP2 has been changed from a semiconductor to metal after adsorbing LiPSs, which is conducive to improving the electrical conductivity of the system. Moreover, due to the low cleavage energy barrier for the conversion of Li2S2 into Li2S, it not only improves the conversion efficiency but also avoids the waste of active substances. Finally, the low energy barrier for the catalytic decomposition of Li2S and the fast diffusion of the Li atom on the substrate accelerates the entire electrochemical process, thereby promoting the cycle performance and coulombic efficiency of Li-S batteries. In view of these advantages, it could expect that the BNP2 monolayer is an excellent anchoring material for Li-S batteries.

Oriented external electric fields act as a “switch” of Pt-M/BC3N2 diatomic catalysts activate pristine ammonia borane dehydrogenation: A DFT study

In this paper, the Pt-M/BC3N2 (M= Ag, Al, Au, Co, Cr, Cu, Fe, Ir, Mn, Mo, Nb, Ni, Pd, Pt, Re, Rh, Ru, Se, Ta, Ti, V, W, Zn, La, Ce, Zr, Hf, Cd, Hg and Y) diatomic catalyst structure was constructed and used to activate Ammonia Borane (AB) under external axial electric field by the First-principles calculation method. By changing the size of applied electric field, we found that the activation of N-H bond in AB can be realized only on Pt-M/BC3N2 (M=Al, Zn, Hf, Y) diatomic catalyst, and the effective electric field range is different. Further calculation showed that Pt-Y/BC3N2 diatomic catalyst could not achieve the break of B-H bond. So, for Pt-M/BC3N2 (M=Al, Zn, Hf) diatomic catalyst, further, sequentially by applying an applied electric field, we achieve the break of the B-H bond in AB and the formation of 1 mol H2. This suggests that the electric field can act as a “switch” for activation of AB molecules.

Study on the mechanism of NOx reduction by NH3-SCR over Mn and M(M=V,Ti) co-doped CoCr2O4 catalyst

Being based on the first-principles calculation method of density functional theory, our work calculated the optimized configuration of CoCr2O4(100) before and after co-doping of Mn and V(Ti). The adsorption behaviors of NH3, NO, NO2 and other gas molecules on the catalyst before and after doping were simulated. The optimized structures and related energy distribution of NH3 dehydrogenation reaction and SCR reaction on Mn0.1Co0.9V0.1Cr1.9O4 and Mn0.1Co0.9Ti0.1Cr1.9O4 catalysts were also fully studied. Our results reveal that the co-doping of heteroatom towards CoCr2O4(100) may result in electron migration and lattice dislocations as well as improving the surface acid activity. Therefore, the co-doping of Mn and V or Mn and Ti are believed to improve the adsorption of NH3, NO, NO2 and other gas molecules on the CoCr2O4 catalyst and significantly reduce the activation energy barrier of the NH3 dehydrogenation reaction and the SCR reaction. Furthermore, we studied the adsorption of SO2 and H2O on the co-doped catalyst, which exhibited that the co-doping of Mn and Ti may effectively improve the water and sulfur resistance of the catalyst. Our research are expected to be full of important theoretical guiding significance for the development, preparation and modification of cobalt-chromium spinel catalysts.

Effects of Cl− substitution on the scintillation properties of Cs2LiLaBr6-xClx:Ce crystals

In this work, an anion-alloying strategy using chloride substitution is used to improve the gamma response performance of cutting-edge Cs2LiLaBr6:Ce single crystal scintillators. Single crystals of Cs2LiLa(Br,Cl)6:Ce (CLLBC:Ce) with a size of Ф12 mm × 50 mm were successfully grown by the Bridgman method. The effects of chloride substitution amount on crystal structure, band structure, luminescence properties and the scintillation properties were systematically investigated. The light yield and energy resolution of CLLB:Ce were enhanced as the increase of Cl− content. The highest light yield and optimal energy resolution were achieved on the Cs2LiLaBr4Cl2:Ce, about 86% of the commercial LaBr3:Ce single crystal and 4.1% at 662 keV. On a basis of the results of first-principle calculation and pure optical method, the band structures of Cs2LiLa(Br,Cl):Ce were constructed, indicating a tendency of band-gap to increase as the Cl− content increases. The origin of light yield improvement was also proposed.

Charge fluctuation of simple substances in 3-dimensional lattices

Using the first-principles calculation method, we calculated the net atomic Hirshfeld charges of 1772 allotropes for 90 elemental substances. 136 allotropes of 44 elemental substances were found charge inhomogeneity in them. There are three types of charge fluctuations in simple substances originated from different local lattice environments: the atomic charge ordering, the cluster charge ordering and atom-interstitial charge ordering. In the periodic table, most of the metal elements have allotropes with non-zero atomic charges. Most main group elements have allotropes with non-zero atomic charges. Fewer elements exhibit atomic charge changes in the subgroup fraction. The atomic charges of group zero and main group seven elements (except Br) are always zero. Self-ionization, polarization, and redox introduced non-zero charges of simple substances in the 3-dimensional lattices mean their non-zero valence or oxidation states. Our computational results further demonstrate the physical properties of the internal structures of fundamental condensed matter.

Influence of doping Sn direction and concentration on vanadium pentoxide based on density functional theory

Based on the first-principles calculation method of density functional theory, the influence of different directions and concentrations of Sn doping on V2O5 was discussed. The doping formation energy, electronic density of states, and isosurface charge density of different Sn doping directions and doping concentration structures are calculated. The calculation results of five different crystal orientation doping models show that the doped structure along the [111] crystal orientation has a smaller doping formation energy of 1.879 eV, which has the best electrical properties and the largest charge density. And the charge distribution is the most concentrated. It is most conducive to the formation of conductive filaments. In addition, as the doping concentration increases, the charge density gradually increases. When the doping concentration is 3.174%, the peak impurity energy level is the highest and the band gap is the smallest. At the same time, there is a tendency to form conductive filaments in the direction of charge extension [111], and the resistance change characteristics of vanadium pentoxide are best improved. The research results of this paper can provide certain theoretical guidance for improving the performance of resistive random access memory based on vanadium pentoxide.

Hydrogen Storage Performance of γ-Graphdiyne Doped Li Based on First Principles for Micro/Nano.

The rapid development of micro/nano systems promotes the progress of micro energy storage devices. As one of the most significant representatives of micro energy storage devices, micro hydrogen fuel cells were initially studied by many laboratories and companies. However, hydrogen storage problems have restricted its further commercialization. The γ-graphdiyne (γ-GDY) has broad application prospects in the fields of energy storage and gas adsorption due to its unique structure with rigid nano-network and numerous uniform pores. However, the existence of various defects in γ-GDY caused varying degrees of influence on gas adsorption performance. In this study, Lithium (Li) was added into the intrinsic γ-GDY and vacancy defect γ-GDY (γ-VGDY) to obtain the Li-GDY and Li-VGDY, respectively. The first-principles calculation method was applied and the hydrogen storage performances of them were analysed. The results indicated that the best adsorption point of intrinsic γ-GDY is H2 point, which located at the centre of a large triangular hole of an acetylene chain. With large capacity hydrogen storage, doping Li atom could improve the hydrogen adsorption property of intrinsic γ-GDY; meanwhile, vacancy defect inspires the hydrogen storage performance further of Li-VGDY. The mass hydrogen storage density for Li2H56-GDY and Li2H56-VGDY model were 13.02% and 14.66%, respectively. Moreover, the Li2H56-GDY and Li2H56-VGDY model had same volumetric storage density, with values that could achieve 5.22 × 104 kg/m3.

Study on the Adsorption Characteristics of Mo-Doped Graphene on the Decomposition Products of SF6 Substitute Gas Based on First-Principle Calculations

C4F7N, C5F10O, etc., as new environmental-friendly alternative gases decompose under partial discharge and produce a series of products such as CO, CF4, C2F6, C3F8, CF3CN, C2F5CN, and COF2. Based on the first-principles calculation method of density functional theory (DFT), the adsorption characteristics of intrinsic state graphene and Mo-doped graphene adsorbing SF6 and its substitute gas decomposition products are calculated and analyzed. By comparing the adsorption energy, adsorption distance, density of state, Mulliken charge population, charge transfer amount, and molecular orbital energy for adsorbing different decomposition gases, it can be seen that the system structure is the most stable when Mo is doped at the T site of the graphene surface. The adsorption of Mo-doped graphene on gas molecules is significantly stronger than that of intrinsic graphene, and the order of adsorption is: SO2F2 > H2S > SO2 > CF4. The adsorption of H2S gas molecules by intrinsic state and Mo-doped graphene is n-type adsorption, while the adsorption of SO2F2, CF4, and SO2 gas molecules is p-type adsorption. Mo-doped graphene can be used as a detection device for SO2F2 gas resistance sensors.

Effect of Mg–Ga alloy intermetallic compounds on the properties of soluble aluminum alloy

Numerous soluble aluminum alloys are the overriding applications in hydraulic fracturing technology applied in oil and gas field exploitation or biomaterial utilization. The solubility of aluminum alloy attributes to that of superficial hard and dense alumina film damage or broken, in such cases several representative low melting point metals addition will play a part, such as Ga, In, Sn, etc. Typically, aluminum alloys tends to be brittle due to Ga addition, while Mg element can be supposed to enhance its strength according to four representative Mg–Ga alloy intermetallic compounds, which is Mg2Ga, MgGa, Mg5Ga2 and MgGa2, respectively. In present article, the first-principles calculation method was introduced to theoretically investigate the mechanical properties of the four Mg–Ga phases. The thermodynamic properties, structural stability, electronic structure, elastic properties and performance under pressure of four Mg–Ga intermetallic compounds were also investigated. Obviously, from the perspective of electronic structure, Mg is the electronic provider and Ga is the electronic acceptor in these compounds. According to the ionization degree calculation, the interaction between Mg and Ga ions in Mg5Ga2 phase is the strongest. In MgGa phase, the s-state electron energy density of Ga atom is the highest, so the s-state electron of Ga atom contributes the most to the contact potential between the grain boundary phase and the Al matrix. Therefore, the driving force of MgGa anodic dissolution has a decisive advantage which is reflected that its corrosion rate and the hydrogen production rate is the maximum. Thus the analysis of four intermetallic compounds mechanical properties, the bulk modulus B of four Mg–Ga intermetallic compounds is basically similar, indicating that they have similar compressive deformation resistance and fracture resistance. At 0 GPa, the young's modulus E and shear modulus G of Mg5Ga2 is the highest. The results show that Mg5Ga2 has the largest stiffness and plastic deformation resistance.

Crystallographic Calculations and First-Principles Calculations of Heterogeneous Nucleation Potency of γ-Fe on La2O2S Particles.

Rare earth (RE) inclusions with high melting points as heterogeneous nucleation in liquid steel have stimulated many recent studies. Evaluating the potency of RE inclusions as heterogeneous nucleation sites of the primary phase is still a challenge. In this work, the edge-to-edge matching (E2EM) model was employed to calculate the atomic matching mismatch and predict the orientation relationship between La2O2S and γ-Fe from a crystallographic point of view. A rough orientation relationship (OR) was predicted with the minimum values of and as follows: ∥ and ∥. The interface energy and bonding characteristics between La2O2S and γ-Fe were calculated on the atomic scale based on a crystallographic study using the first-principles calculation method. The calculations of the interface energy showed that the S-terminated and La(S)-terminated interface structures were more stable. The results of difference charge density, electron localization function (ELF), the Bader charges and the partial density of states (PDOS) study indicated that the La(S)-terminated interface possessed metallic bonds and ionic bonds, and the S-terminated interface exhibited metallic bond and covalent bond characteristics. This work addressed the stability and the characteristics of the La2O2S/γ-Fe interface structure from the standpoint of crystallography and energetics, which provides an effective theoretical support to the study the heterogeneous nucleation mechanism. As a result, La2O2S particles are not an effective heterogeneous nucleation site for the γ-Fe matrix from crystallography and energetics points of view.

Combined first-principles and machine learning study of the initial growth of carbon nanomaterials on metal surfaces

To understand the effects of H of hydrocarbon precursors and alloying elements of catalysts on the initial growth of carbon nanomaterials, this work combined first-principles (FP) calculation and machine learning (ML) methods to study the adsorption of complete hydrocarbon molecules on various alloy surfaces. Specifically, we calculated the energetics and geometries of the adsorption of acetylene (C2H2) molecules on the pristine Ni, Co, and Fe metal and a benzene molecule on Ni-X [X = thirty 3d, 4d, and 5d transition metal (TM) elements] alloy surfaces. The results suggest that benzene has larger adsorption energies on Ni-X (X = Y, Cd, Sc, Lu, Ag, Ti, Hg, Pd, Zn, V, Cu, and Au) than that on the pristine Ni surface. Furthermore, the ML models were constructed using the surface “Center-Environment” (SCE) features to predict the FP results. The ML models suggest that the features critical to adsorption energies include the size, electronegativity, and valence of the doping element. We proposed an “add and dehydrogenate” mechanism underlying the initial growth of nanocarbon with hydrocarbon precursors. These results provide a theoretical basis in the design of alloy catalysts including in-plane single atom catalysts.