Prediction of semiconducting SiP_2 monolayer with negative Possion's ratio,ultrahigh carrier mobility and CO_2 capture ability

Using particle swarm optimization(PSO) methodology for crystal structure prediction,we predicted a novel two-dimensional(2 D) monolayer of silicide diphosphorus compound:SiP_2,which exhibits good stability as examined via cohesive energy,mechanical criteria,molecular dynamics simulation and all positive phonon spectrum,respectively.The SiP_2 monolayer is an indirect semiconductor with the band gap as 1.8484 eV(PBE) or 2.681 eV(HSE06),which makes it more advantageous for high-frequencyresponse optoelectronic materials.Moreover,the monolayer is a relatively hard auxetic material with negative Possion's ratios,and also possesses a ultrahigh carrier mobility(1.069 × 10~5 cm~2 V~1 s~1) which is approximately four times the maximum value in phosphorene and comparable to the value of graphene and CP monolayers.Furthermore,the effects of strains on band structures and optical properties of SiP2 monolayer have been studied,as well as CO_2 molecules can be strongly chemically adsorbed on the SiP_2 monolayer.A semiconductor-to-metal transition for-9.5% strain ratio case and a huge optical absorption capacity on the order of 106 cm ~1 in visible region present.These theoretical findings endow SiP2 Monolayer to be a novel 2 D material holding great promises for applications in highperformance electronics,optoelectronics,mechanics and CO_2 capturing material.     

Cr、Sn、Co掺杂对层状二维材料MoSi2N4的电子和光学性能的影响

基于新合成的二维材料MoSi₂N₄（MSN）,我们建立了一系列MSN的掺杂模型进行了第一原理计算。首先,我们计算了本征MSN的电子特性,包括其能带结构和态密度。然后我们研究了Cr、Sn和Co掺杂对MSN的电子和光学性质的影响。结果表明,在3种掺杂体系中,Co掺杂体系表现出最低的形成能,这表明Co掺杂体系是最稳定的。通过带隙计算表明,尽管3种掺杂模型都降低了MSN的固有带隙,但却表现出3种不同的电子特性。态密度图也显示,Cr和Co掺杂体系都在导带底（CBM）和价带顶（VBM）附近产生局部尖峰。此外,光学性质的计算中表明,掺杂后体系的光学性质也得到了改善。     

Investigation of structural,magneto‐electronic,and thermoelectric response of ductile SnAlO3 from high‐throughput DFT calculations

Successfully optimized calculations for the stability of SnAlO₃ perovskite in its paramagnetic phase and various structural parameters have been figured out in this study. Structural stability and ductile character is reflected from the calculated elastic constants and mechanical properties. Moreover, the melting temperature of the present material has also been calculated. We have discussed in detail, the ground state electronic band structure and paramagnetic character. In addition, the Boltzmann's transport theory has been employed to obtain the Seebeck, electrical and thermal conductivity coefficients so as to manifest the thermoelectric response of the material. Remarkably, the observed high electrical conductivity in inclusion of metallicity and paramagnetic nature is a characteristic of perovskite type electrode materials. The above discussed material properties suggest the possible application of this compound as an efficient electrode material.     

Electronic Structures and Thermoelectric Properties of Two-Dimensional MoS2/MoSe2 Heterostructures

Thermoelectric properties of bulk and bilayer two-dimensional (2D) MoS₂/MoSe₂ heterostructures are investigated using density functional theory in conjunction with semiclassical Boltzmann transport theory. It is predicted that the bulk 2D heterostructures could considerably enhance the thermoelectric properties as compared with the bulk MoSe₂. The enhancement originates from the reduction in the band gap and the presence of interlayer van der Waals interactions. We therefore propose the 2D MoS₂/MoSe₂ heterostructures as a possible candidate material for thermoelectric applications.     

Theoretical study of the structure and fundamental properties of AZn2N2 (A = Ca,Sr, Ba)

The structure, stability, elastic, electronic, and optical properties of trigonal AZn₂N₂ (A = Ca, Sr, Ba) are simulated and compared in this work. The stability and physical properties of BaZn₂N₂ are mainly highlighted. According to the calculated results, three compounds are thermodynamically and mechanically stable, and they are brittle materials. The stability of trigonal BaZn₂N₂ is confirmed by using the different theoretical approaches. The direct band gap transition is allowed at the Γ point for each compound. The predicted direct band gaps are 1.733, 1.507, and 1.510 eV for CaZn₂N₂, SrZn₂N₂, and BaZn₂N₂, respectively. The valence band is mostly composed of the N-2p orbitals, while the conduction band is mainly contributed from the Ca-3d/Sr-4d/Ba-5d orbitals. The results show that the electron shows high mobility for carrier transport, and the value of exciton binding energy is less than 80 meV. Furthermore, compared to CaZn₂N₂ and SrZn₂N₂, BaZn₂N₂ shows excellent light absorption capacity in the visible region. This study indicates that BaZn₂N₂ is a desirable material for solar cell applications.     

Access to Novel Graphene‐Like Sheet of Hydroboron: First‐Principles Investigation

We designed a cyclic borane (B₆H₁₂) molecule with a benzene‐like structure, in which the six B atoms are located in the same plane. Three methods of B3LYP, MP2, and CCSD with the 6‐311++G** basis were used to investigate its structure, electronic property, and stability. Next, we calculated the stability and electronic property of three hydroboron derivatives with fused rings of B₁₀H₁₈, B₁₄H₂₄, and B₁₆H₂₆. Finally, we investigated three types of novel two‐dimensional infinite hydroboron sheets with diborane as a building block. The results of the phonon spectra ensure the dynamic stability of these predicted structures. Furthermore, the three types of hydroboron sheets are shown to have different band gap energies of less than 3.0 eV. Some investigations on the optical properties have also been performed. The predicted sheets are candidates for semiconductors, whose band gap energy can be tuned by the positions of the bridge hydrogen atoms in the sheets.     

Structural,Thermal, and Electronic Properties of Two-Dimensional Gallium Oxide (β-Ga2O3) from First-Principles Design

Two-dimensional (2D) materials with exotic electronic, optical and mechanical properties have attracted tremendous attention in the last two decades, due to their potential applications in electronics, energy storage and conversion technologies. However, only a few dozen 2D materials have been successfully synthesized or exfoliated. Motivated by the recent discovery of 2D gallenene, we have explored new 2D allotropes of β-Ga₂O₃, an emerging wide-band gap transparent conductive oxide (TCO) with a wide range of semiconducting applications. All the possible 2D allotropes of β-Ga₂O₃ with high energetic stability have been predicted using particle swarm optimization, combined with density functional theory calculations. The structural and dynamical stability of the predicted 2D allotropes has been analyzed. Although β-Ga₂O₃ is not a van der Waals material, results predict that one or two allotropes of β-Ga₂O₃ are stable. In addition, the accurate band structures of these 2D semiconducting oxides have been calculated using both the GGA and LDA-1/2 approach. Remarkably, monolayer Ga₂O₃(100) has a larger indirect band gap of 4 eV, demonstrating a new avenue for the discovery of 2D β-Ga₂O₃ based nano-devices with enhanced electronic properties.     

Two-dimensional 1T-PS2 as a promising anode material for sodium-ion batteries with ultra-high capacity,low average voltage and appropriate mobility

As electrodes, two-dimensional materials show special advantages including the infinite planar lengths, broad electrochemical window, large surface–volume ratio, and much exposed active sites. In theory, the two-dimensional materials consist of the elements with high electronegativity may absorb more Na atoms, resulting in a high battery storage capacity. Based on the above idea, we selected the two dimensional metallic PS₂ with 1T-Type structure as an anode material, and explored its potential applications as an electrode material for Na-ion battery through first-principle calculations. As we expected, when two dimensional PS₂ is used as an anode in Na-ion battery, it can adsorb maximum three layers of sodium atoms on both sides of the monolayer, resulting in a maximum theoretical capacity of 1692 mAh/g. Furthermore, it also possesses a rather small sodium diffusion barrier of 0.17 eV, a low average open-circuit voltage of 0.18 V, and a relatively small lattice changes within 13% during the intercalation of Na. These results suggested that the two dimensional PS₂ is a potentially excellent Na-ion battery anode. Our idea of designing two-dimensional anode materials with high storage capacity may provide some references for designing the next generation anode materials of metal-ion batteries.     

Molecular engineering of CxNy: Topologies,electronic structures and multidisciplinary applications

As a class of metal-free two-dimensional (2D) semiconductor materials, polymeric carbon nitrides have attracted wide attention recently due to its facile regulation of the molecular and electronic structures, availability in abundance and high stability. According to the different ratios of C and N atoms in the framework, a series of C_xN_y materials have been successfully synthesized by virtue of various precursors, which further triggers extensive investigations of broad applications ranging from sustainable photocatalytic reactions and highly sensitive optoelectronic biosensing. In view of topological structures on their electronic structures and material properties, the as-reported C_xN_y could be generally classified into two main categories with three- or six-bond-extending frameworks. Owing to the effective n→π* transition in most C_xN_y materials, the relative energy level of the lone-pair electrons on N atoms is high, which thus endows the materials with the capability of visible light absorption. Meanwhile, the different repeating units, bridging groups and defect sites of these two kinds of C_xN_y allow them to effectively drive a diverse of promising applications that require specific electronic, interfacial and geometric properties. This review paper aims to summarize the recent progress in topological structure design and the relevant electronic band structures and striking properties of C_xN_y materials. In the final part, we also discuss the existing challenges of C_xN_y and outlook the prospect possibilities.     

Oxygen Vacancy Engineering in Titanium Dioxide for Sodium Storage

Titanium dioxide (TiO₂) is a promising anode material for sodium-ion batteries (SIBs) due to its low cost, natural abundance, nontoxicity, and excellent electrochemical stability. Oxygen vacancies, the most common point defects in TiO₂, can dramatically influence the physical and chemical properties of TiO₂, including band structure, crystal structure and adsorption properties. Recent studies have demonstrated that oxygen-deficient TiO₂ can significantly enhance sodium storage performance. Considering the importance of oxygen vacancies in modifying the properties of TiO₂, the structural properties, common synthesis strategies, characterization techniques, as well as the contribution of oxygen-deficient TiO₂ on initial Coulombic efficiency, cyclic stability, rate performance for sodium storage are comprehensively described in this review. Finally, some perspectives on the challenge and future opportunities for the development of oxygen-deficient TiO₂ are proposed.     

First-Principles Study on Electronic and Optical Properties of Graphene-Like Boron Phosphide Sheets

Two-dimensional semiconducting materials with moderate band gap and high carrier mobil-ity have a wide range of applications for electronics and optoelectronics in nanoscale. On the basis of first-principles calculations, we perform a comprehensive study on the electronics and optical properties of graphene-like boron phosphide (BP) sheets. The global structure search and first-principles based molecular dynamic simulation indicate that two-dimensional BP sheet has a graphene-like global minimum structure with high stability. BP monolayer is semiconductor with a direct band gap of 1.37 eV, which reduces with the number of layers. Moreover, the band gaps of BP sheets are insensitive to the applied uniaxial strain.= The calculated mobility of electrons in BP monolayer is as high as 10⁶ cm²/(V·s). Lastly, the MoS₂/BP van der Waals heterobilayers are investigated for photovoltaic applications, and their power conversion efficiencies are estimated to be in the range of 17.7%－19.7%. This study implies the potential applications of graphene-like BP sheets for electronic and optoelectronic devices in nanoscale.     

A Novel Quasi-Planar Two-dimensional Carbon Sulfide with Negative Poisson's Ratio and Dirac Fermions

In the present study, a novel and unconventional two-dimensional (2D) material with Dirac electronic features has been designed using sulflower with the help of density functional theory methods and first principles calculations. This 2D material comprises of hetero atoms (C, S) and belongs to the tetragonal lattice with P₄/nmm space group. Scrutiny of the results show that the 2D nanosheet exhibits a nanoporous wave-like geometrical structure. Quantum molecular dynamics simulations and phonon mode analysis emphasize the dynamical and thermal stability. The novel 2D nanosheet is an auxetic material with an anisotropy in the in-plane mechanical properties. Both composition and geometrical features are completely different from the conditions necessary for the formation of Dirac cones in graphene. However, the presence of semi-metallic nature, linear band dispersion relation, massive fermions and massless Dirac fermions are observed in the novel 2D nanosheet. The massless Dirac fermions exhibit highly isotropic Fermi velocities (v_f=0.68×10⁶ m/s) along all crystallographic directions. The zero-band gap semi metallic features of the novel 2D nanosheet are perturbative to the electric field and external strain.     

Automated search for new thermoelectric materials: the case of LiZnSb

An automated band structure calculation based on the inorganic crystal structure database and the augmented plane wave method for electronic structure calculations is presented. Using a rigid band approach and semiclassic Boltzmann theory the band structures are analyzed and a large number of compounds are screened for potential interesting thermoelectric properties. We thereby propose LiZnSb as a potential new thermoelectric material. The k-space structure of the lowest conduction band of LiZnSb is analyzed in detail, and excellent thermoelectric properties are expected for this material. Furthermore the lattice dynamics are calculated, and anisotropic lattice thermal conduction is predicted.     

Ab-initio calculation of structural, electronic, and optical characterizations of the intermetallic trialuminides ScAl3 compound

We present first-principles study of the electronic and the optical properties for the intermetallic trialuminides ScAl₃ compound using the full-potential linear augmented plane wave method within density-functional theory. We have employed the generalized gradient approximation (GGA), which is based on exchange-correlation energy optimization to calculate the total energy. Also we have used the Engel-Vosko GGA formalism, which optimizes the corresponding potential for calculating the electronic band structure and optical properties. The electronic specific heat coefficient (γ), which is a function of density of states, can be calculated from the density of states at Fermi energy N(E_F). The N(E_F) of the phase L1₂ is found to be lower than that of D0₂₂ structure which confirms the stability of L1₂ structure. We found that the dispersion of the band structure of D0₂₂ is denser than L1₂ phase. The linear optical properties were calculated. The evaluations are based on calculations of the energy band structure.     

Be2C Monolayer with Quasi‐Planar Hexacoordinate Carbons: A Global Minimum Structure

The design of new materials is an important subject in order to attain new properties and applications, and it is of particular interest when some peculiar topological properties such as reduced dimensionality and rule‐breaking chemical bonding are involved. In this work, we designed a novel two‐dimensional (2D) inorganic material, namely Be₂C monolayer, by comprehensive density functional theory (DFT) computations. In Be₂C monolayer, each carbon atom binds to six Be atoms in an almost planar fashion, forming a quasi‐planar hexacoordinate carbon (phC) moiety. Be₂C monolayer has good stability and is the lowest‐energy structure in 2D space confirmed by a global minima search based on the particle‐swarm optimization (PSO) method. As a semiconductor with a direct medium band gap, Be₂C monolayer is promising for applications in electronics and optoelectronics.     

A First-Principles Study on the Adsorption of Small Molecules on Arsenene: Comparison of Oxidation Kinetics in Arsenene,Antimonene, Phosphorene,and InSe

Arsenene, a new group-V two-dimensional (2D) semiconducting material beyond phosphorene and antimonene, has recently gained an increasing attention owning to its various interesting properties which can be altered or intentionally functionalized by chemical reactions with various molecules. This work provides a systematic study on the interactions of arsenene with the small molecules, including H₂, NH₃, O₂, H₂O, NO, and NO₂. It is predicted that O₂, H₂O, NO, and NO₂ are strong acceptors, while NH₃ serves as a donor. Importantly, it is shown a negligible charge transfer between H₂ and arsenene which is ten times lower than that between H₂ and phosphorene and about thousand times lower than that between H₂ and InSe and antimonene. The calculated energy barrier for O₂ splitting on arsenene is found to be as low as 0.67 eV. Thus, pristine arsenene may easily oxidize in ambient conditions as other group V 2D materials. On the other hand, the acceptor role of H₂O on arsenene, similarly to the cases of antimonene and InSe, may help to prevent the proton transfer between H₂O and O− species by forming acids, which suppresses further structural degradation of arsenene. The structural decomposition of the 2D layers upon interaction with the environment may be avoided due to the acceptor role of H₂O molecules as the study predicts from the comparison of common group V 2D materials. However, the protection for arsenene is still required due to its strong interaction with other small environmental molecules. The present work renders the possible ways to protect arsenene from structure degradation and to modulate its electronic properties, which is useful for the material synthesis, storage and applications.     

Integrated Reversible Thermochromism,High Tc,Dielectric Switch and Narrow Band Gap in One Multifunctional Ferroic

Organic-inorganic Hybrid (OIH) materials for multifunctional switchable applications have attracted enormous attention in recent years due to their excellent optoelectronic properties and good structural tunability. However, it still remains challenging to fabricate one simple OIH compound with multi-functionals properties, such as dielectric switching, thermochromic properties, semiconductor characteristics and ferroelasticity. Under this context, we successfully synthesized [2-(2-fluorophenyl)ethan-1- ammonium]₂SnBr₆ (compound 1 ), which has a higher phase transition temperature of 427.7 K. Additionally, it exhibits a semiconducting property with an indirect band gap of 2.36 eV. Combining ferroelastic, narrow band gap, thermochromic, and dielectric properties, compound 1 can be considered as a rarely reported multi-functional ferroelastic material, which is expected to give inspiration for broadening the applications in the smart devices field.     

The two-dimensional band structure of (polyphthalocyaninato)Ni(II)

The two-dimensional (2D) band structure of (polyphthalocyaninato)Ni(II), Ni(ppc), has been analyzed by a self-consistent field (SCF ) Hartree–Fock (HF ) crystal orbital (CO ) formalism based on an INDO (intermediate neglect of differential overlap) type Hamiltonian. The calculated HF band gap of Ni(ppc) amounts to 0.24 eV. The highest filled band is a ringlike a_1u combination (D_4h symmetry label) localized at the carbon sites of the organic fragment. Remarkable hybridization in the valence band leads to the considerable band width Δ?_v of 2.92 eV. This value is close to the Δ?_v numbers which are conventionally encountered in one-dimensional metallomacrocycles. The effective width of the states in Ni(ppc) is 13.8 eV. In graphite a net π interval of 13.0 eV is predicted by the present CO formalism; i.e., the energetic distribution of the π electrons is roughly comparable in both 2D solids. The Ni 3d states in Ni(ppc) are far below the Fermi level which is calculated at ?4.9 eV; they are predicted between ?12.2 and ?16.4 eV in the mean-field approximation. Quasi-particle corrections lead to a significant shift of these strongly metal-centered states. Important electronic structure properties of Ni(ppc) are compared with those of 1D metallomacrocycles with similar molecular stoichiometry. The total density of states distribution of Ni(ppc) has been fragmented into projected (ligand π and σ, Ni 3d) contributions in order to allow for a transparent interpretation of the 2D band structure.     

Comparative study of the electronic structure of alkaline-earth borides (MeB2; Me=Mg, Al, Zr, Nb, and Ta) and their normal-state conductivity

By means of density functional theory the electronic structure of the MgB₂ superconductor was characterized and compared with that of the related iso-structural systems: AlB₂, ZrB₂, NbB₂, and TaB₂. Using the full potential-linearized augmented plane wave (FP-LAPW) method and the generalized gradient approximation, the electronic density distribution, density of states, and band structures were obtained for these compounds. The electrical conductivity, which cannot be easily measured in the c-direction, was calculated, in the relaxation time approximation using band structure results. It was found that the two-dimensional (2D) crystal structure character of these metallic diborides is also reflected in the electronic charge distribution. This 2D pattern is not reproduced in the electrical conductivity as it is, for instance, in the superconductor high T_c cuprates. The calculations indicate a bulk, yet anisotropic, conductivity for all these compounds.