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By means of the particle-swarm optimization method and density functional theory calculations, the lowestenergy structure of SnAs is determined to be a bilayer stacking system and the atoms on top of each other are of the same types. Using the hybrid functional of Heyd–Scuseria–Ernzerhof, SnAs is calculated to be a semiconductor with an indirect band gap of 1.71 eV, which decreases to 1.42 eV with the increase of the bi-axial tensile stress up to 2%, corresponding to the ideal value of 1.40 eV for potential photovoltaic applications. Based on the deformation potential theory, the two-dimensional(2 D) SnAs has high electron motilities along x and y directions(1.63 × 10~3 cm~2 V~(-1)s~(-1)). Our calculated results suggest that SnAs can be viewed as a new type of 2 D materials for applications in optoelectronics and nanoelectronic devices. 相似文献
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运用以密度泛函理论为基础的相对论性离散变分方法(DV-Xα)模拟计算了完整的和含有F心、F+心以及F2心的碘化铯(CsI)晶体的电子结构,得到了含F心和F+心以及F2心的CsI晶体电子态密度分布以及它们可能产生的光学跃迁模式.计算结果表明,含F心和F2心的CsI晶体的禁带宽度明显变窄,F心和F2心的能级都出现在禁带中并且作为施主能级位于导带底部,利用过渡态理论计算得到其能级向Cs的5d轨道发生光学跃迁,能量跃迁值分别为1.69eV和1.15eV,该结果与实验结果完全一致,F+心没有能级出现在禁带中.计算结果从理论上成功地解释了碘化铯晶体经过辐照后电子型色心所产生的吸收带起源问题. 相似文献
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采用基于密度泛函理论的第一性原理方法,对新近发现的四方Mo2B在0~40 GPa压力范围内的物性进行了研究,研究内容包括弹性、各向异性、脆性延展性、硬度、理论强度、热容、热膨胀系数等基本物理性质.研究发现在0~40 GPa压力范围内,四方Mo2B晶体均满足力学稳定性条件,并且表现出较强的各向同性.同时发现该晶体具有较高的抗压缩能力,但抗剪切能力较差,抗压和抗剪切能力会随压力增加而增长.此外还发现四方Mo2B为韧性材料,且压力越大韧性越强.计算显示它的维氏硬度为14.3 GPa,限制其作为超硬材料的应用.通过应力-应变的计算发现其不同方向的理想拉伸及剪切强度都比较低.此外,还利用准谐德拜模型研究了四方Mo2B的热膨胀系数以及定容热容等热力学性质. 相似文献
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采用第一性原理计算方法,通过改变Zn1-xBexO合金中Be的浓度及其掺杂位型,研究N在Zn1-xBexO合金中的形成能和受主离化能,分析了p型导电的可能性.结果表明:Be-N共掺杂时,N优先占据周围没有Be的O位置,每增加一个Be近邻掺杂原子,No的形成能增加约0.2 eV.当近邻Be原子数为2和3时,No的受主离化能比较低.Be浓度为11at;时,具有2个近邻Be原子的No的受主离化能降低至0.1 eV左右,可以认为是浅受主,Be-N共掺ZnO才可能呈p型导电.考虑No在室温条件下的受主离化率和No形成能的影响,估算出Be-N所提供的空穴载流子浓度不会高于1017 cm-3;如果计及n型背景载流子的补偿效应,Be-N共掺ZnO的p型导电率应该比较低. 相似文献
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Mechanical and thermodynamic properties of the monoclinic and orthorhombic phases of SiC_2N_4 under high pressure from first principles
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First principles calculations are preformed to systematically investigate the electronic structures, elastic and thermodynamic properties of the monoclinic and orthorhombic phases of Si C2N4 under pressure. The calculated structural parameters and elastic moduli are in good agreement with the available theoretical values at zero pressure. The elastic constants of the two phases under pressure are calculated by stress–strain method. It is found that both phases satisfy the mechanical stability criteria within 60 GPa. With the increase of pressure, the degree of the anisotropy decreases rapidly in the monoclinic phase, whereas it remains almost constant in the orthorhombic phase. Furthermore, using the hybrid density-functional theory, the monoclinic and orthorhombic phases are found to be wide band-gap semiconductors with band gaps of about 2.85 e V and 3.21 e V, respectively. The elastic moduli, ductile or brittle behaviors, compressional and shear wave velocities as well as Debye temperatures as a function of pressure in both phases are also investigated in detail. 相似文献
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采用射频磁控溅射技术, 在不同温度下制备了N掺杂Cu2O薄膜.透射光谱分析发现, N掺杂导致Cu2O成为允许的带隙直接跃迁半导体, 并使Cu2O的光学禁带宽度增加.不同温度下沉积的薄膜光学禁带宽度Eg=2.52± 0.03 eV.第一性原理计算表明, N掺杂导致Cu2O的禁带宽度增加了约25%, 主要与价带顶下移和导带底上移有关, 与实验报道基本符合.N的2p电子态分布不同于O原子, 在价带顶附近具有较大的态密度是N掺杂Cu2O变成允许的带隙直接跃迁半导体的根本原因. 相似文献
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Structure prediction,electronic, and mechanical properties of alkali metal MB_(12)(=Be,Mg, Ca,Sr) from first principles
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Using the particle swarm optimization algorithm on structural search methods, we focus our crystal structures search on boron-rich alkali metal compounds of MB12(M = Be, Mg, Ca, Sr) with simulation cell sizes of 1–2 formula units(f.u.)at 0 GPa. The structure, electronic, and mechanical properties of MB12 are obtained from the density functional theory using the plane-wave pseudopotential method within the generalized gradient approximations. The formation enthalpies of MB12 regarding to solid metal M and solid alpha-boron suggested the predicted structures can be synthesized except for BeB12. The calculated band structures show MB12(M = Be, Mg, Ca, Sr) are all indirect semiconductors. All the calculated elastic constants of MB12 satisfy the the mechanical stable conditions. The mechanical parameters(i.e., bulk modulus,shear modulus, and Young’s modulus) are derived using the Voigt–Reuss–Hill method. The G/B ratios indicated that the MB12 should exhibit brittle behavior. In addition, the hardness, Debye temperature, universal anisotropic index, and the percentage of anisotropy in compression and shear are also discussed in detail. We hope our results can inspire further experimental study on these boron-rich alkali-metal compounds. 相似文献
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Elastic and thermodynamic properties of vanadium nitride under pressure and the effect of metallic bonding on its hardness
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By the particle-swarm optimization method, it is predicted that tetragonal P42mc, 141md, and orthorhombic Amm2 phases of vanadium nitride (VN) are energetically more stable than NaCl-type structure at 0 K. The enthalpies of the predicted three new VN phases, along with WC, NaC1, AsNi, CsCl type structures, are calculated each as a function of pressure. It is found that VN exhibits the WC-to-CsCl type phase transition at 256 GPa. For the considered seven crystal- lographic VN phases, the structures, elastic constants, bulk moduli, shear moduli, and Debye temperatures are investigated. Our calculated equilibrium structural parameters are in very good agreement with the available experimental results and the previous theoretical results for the NaC1 phase. The Debye temperatures of VN predicted three novel phases, which are all higher than those of the remaining structures. The elastic constants, thermodynamic properties, and elastic anisotropies of VN under pressure are obtained and the mechanical stabilities are analyzed in detail based on the mechanical stability criteria. Moreover, the effect of metallic bonding on the hardness of VN is also investigated, which shows that VNs in P42mc, 141md, and Amm2 phases are potential superhard phases. Further investigation on the experimental level is highly recommended to confirm our calculations presented in this paper. 相似文献
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