BaSe的准粒子能带结构

运用标准的准粒子GW方法重新考察了BaSe的准粒子能带结构.为便于比较，同时计算了局域密度近似(LDA)和广义梯度近似(GGA)下的能带.结果表明，LDA和GGA方法都不能准确描述这个材料的带隙.与实验测量值对比，其误差分别达到39.9%和32.6%.GW准粒子能带的结果则可以对其带隙作出大幅度的修正，得到与实验测量相当符合的理论结果.与已有的计算结果不同，B1结构BaSe准粒子能带具有Γ点直接带隙特性，表明在Ba价电子组态中考虑4d电子的作用至关重要. 关键词： BaSe GW 能带结构 带隙     

能带论自洽LMTO方法计算金属铜的零温物态方程

 用密度泛函框架下的自洽LMTO方法，在计算一系列晶格常数的Cu的能带结构的基础上，计算了Cu的零温物态方程。压缩度为1.0～4.5。计算结果与两种基于实验数据的半经验方法所得结果以及Albers等人的计算结果进行了比较，其高压部分亦与带量子交换修正的TFC模型结果作了比较，说明计算结果是合理的。进一步的研究可为修正半经验方法提供依据。弄清与TFC理论的异同，对多体系统相互作用有更进一步的了解。     

用hartree等三种方法计算固体电子能带结构的讨论

本文对用于固体电子能带结构计算的Ｈａｒｔｒｅｅ 方法、 Ｈａｒｔｒｅｅ－Ｆｏｃｋ方法和 Ｋｏｈｎ—Ｓｈａｍ方法在方 程形式、物理概念、适用范围以及存在的缺陷等方面 进行了详细的讨论．     

石墨烯能带结构的紧束缚近似计算

固体能带理论是固体物理学的一个重要理论基础,被广泛应用于材料电学性质的研究。为结合科学前沿教学,以当前热门材料石墨烯为例,介绍紧束缚近似法在石墨烯能带结构计算上的详细过程,并借助Matlab软件展示了其能带结构,进而从理论上解释石墨烯所具有的独特电学性质。     

Slater绝缘体的磁性和能带计算研究

Slater相变是一种由于反铁磁序形成而导致的金属—绝缘体相变.本文采用第一性原理密度泛函计算方法研究了两种Slater绝缘体材料NaOsO_3和Cd_2Os_2O_7的电子结构,进而研究了反铁磁序排列、自旋轨道耦合和电子关联对其电子结构以及相变性质的影响.研究结果表明,非磁相的NaOsO_3具有金属性;而G型线性反铁磁结构是驱动NaOsO_3发生Slater相变的磁基态.此外,研究结果表明,非磁相的焦绿石Cd_2Os_2O_7的能带结构在费米能级处是连续的,表现为金属性;并且带有磁阻挫的Cd_2Os_2O_7发生Slater相变的条件十分苛刻,只有在自旋轨道耦合和1.8 eV电子关联的共同作用下一种全进—全出非线性反铁磁结构才能使其发生Slater相变.说明全进—全出非线性反铁磁结构是使Cd_2Os_2O_7发生Slater相变的磁基态,而自旋轨道耦合和1.8 eV的电子关联在消除磁阻挫上起到了关键作用.     

空位对纤锌矿型AlN自发极化影响的最大局域化Wannier函数方法研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,计算了纤锌矿型AlN中引入不同电荷态的N空位和Al空位时结构中最大局域化Wannier函数,并根据Wannier函数的空间分布及空间分布的几何中心位置,对空位引起的晶体电子结构变化及[0001],[ˉ1010],[ˉ12ˉ10]晶向上的自发极化进行了研究.结果表明,利用最大局域化Wannier函数分析电子结构具有直观的特点,清晰地表明N—Al键具有较强的离子性.研究发现,N空位结构中悬挂键上电荷向空位处转移,而Al空位结构中悬挂键上电荷则远离空位,沿悬挂键方向移动到N原子一侧.同时发现,空位的引入破坏了[ˉ1010],[ˉ12ˉ10]晶向上的中心对称结构,产生了极化,且极化强度随着空位电荷态的增加而增大.在[0001]晶向上,随着N空位电荷态的增加,空位周围电子结构发生了剧烈变化,使得自发极化发生了逆转,极化强度随着电荷态的增加而增大;而在Al空位中,随着电荷态的增加,自发极化沿原方向显著增加,但没有发生极化反转.     

由介质球构成的三维光子晶体能带结构的平面波研究

采用平面波展开方法计算由介质球构成的面心立方三维光子晶体的能带结构及透射性质.选 用合适的平面波个数研究了SiO₂蛋白石结构光子晶体的能带及透射性质，并采 用转移矩阵 方法计算了电磁波沿［111］方向的传输特性，两种方法得到的结果相符合.还研究了反蛋白 石结构光子晶体的全带隙.最后，研究了壳层介质球构成的面心立方结构光子晶体的能带特 性，发现在高介质球外面包裹适当厚度的低介电常数介质壳层所构成的光子晶体，可以增大 L点相对带隙宽度50％，并证明了其优化内外半径比值约为0．69. 关键词： 光子晶体 光子能带 平面波展开方法 Core-Shell结构     

掺铝3C-SiC电子结构的第一性原理计算及其微波介电性能

采用基于密度泛函理论的第一性原理平面波超软赝势法,对比研究了未掺杂和Al掺杂3C-SiC材料的电子结构和介电常数.结果表明:Al掺杂后,Fermi能级进入价带,带隙宽度略为加宽,在8.2—12.4 GHz范围内介电常数大幅度增大.利用燃烧合成法制备了Al掺杂的3C-SiC粉体吸收剂,通过矢量网络分析仪测试了样品在8.2—12.4 GHz范围内的微波介电常数,验证了理论计算结果,并讨论了微波损耗机理.     

Empirical pseudopotential band structure parameters of 4H-SiC using a genetic algorithm fitting routine

In this paper, the viability of using a genetic algorithm to find band structure parameters for empirical pseudopotential method (EPM) calculations is demonstrated by applying a genetic algorithm to find the EPM parameters for 4H-SiC. The form of the pseudopotential for 4H-SiC and the 19 form factors found by the genetic algorithm to fit the band structure to experimentally measured indirect energy gap and direct optical gaps are given. In addition, the effective masses for the conduction band minimum are extracted from the calculated band structure. It is shown that the genetic algorithm provides an effective, automated way to find parameters that give reasonably good fits to both the band gaps and the effective masses simultaneously.     

Quasiparticle band structure and optical properties of NH3BH3

The quasiparticle band structure of the low temperature orthorhombic phase of NH₃BH₃ is studied by using the GW approximation. It is found that NH₃BH₃ is an insulator with a value of the band gap of 5.90 eV with GGA and of 9.60 eV with the GW approximation. Then, the optical properties of NH₃BH₃ are obtained by the calculation of the dielectric function, corrected by a scissor shift operation corresponding to the GW correction on the band gap. Also, the optical anisotropy in NH₃BH₃ is analyzed through the refractive index and static dielectric constants along the different crystallographic directions. Finally, it is found that the energy loss function has a prominent peak at 22.26 eV; at these frequencies (above 22.26 eV) NH₃BH₃ becomes transparent. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electronic band structure and optical properties of silicon nanoporous pillar array

Silicon nanoporous pillar array (Si-NPA) is fabricated by hydrothermally etching single crystal silicon (c-Si) wafers in hydrofluoric acid containing ferric nitrate. Microstructure studies disclosed that it is a typical micron/nanometer structural composite system with clear hierarchical structures. The optical parameters of Si-NPA were calculated by general light-absorption theory and Kramers–Kronig relations based on the experimental data of reflectance and the variations compared with the counterparts of c-Si were analyzed. The features of the electronic band structure deduced from the optical measurements strongly indicate that Si-NPA material is a direct-band-gap semiconductor and possesses separated conduction sub-bands which accords with conduction band splitting caused by silicon nanocrystallites several nanometers in size. All these electronic and optical results are due to the quantum confinement effect of the carriers in silicon nanocrystallites.     

Quadratic augmented plane wave method for self-consistent band structure calculations

Recently linearized versions of the augmented plane wave (APW) method have been introduced. The quadratic-APW (QAPW) method is presented which is a more general formulation of the linear-APW (LAPW) methods. Here the exact radial solution inside the muffin-tin (MT) sphere is replaced by its Taylor expansion with respect to the energy, truncated after the quadratic term, i.e. with higher accuracy when compared with the standard LAPW method which uses only the linear term. The standard LAPW method is obtained as a special case from our formulation. Similarly to the standard LAPW method, the energy independent APW's are formed from approximate radial wave functions which lead to the secular equations linear in energy. The analysis of the solution inside the MT-sphere shows that the eigenvalue error is proportional to (E-E ₀)⁶ in the method suggested as compared with (E-E ⁰)⁴ for the standard LAPW method. As an application both non-self-consistent and self-consistent calculations are presented for the band structure of FCC copper metal.     

Electronic band structure calculation of GaNAsBi alloys and effective mass study

Electronic band structures of GaN_xAs_1−x−yBi_y dilute nitrides–bismides have been determined theoretically within the framework of the band anticrossing (BAC) model and k ⋅ p method. We have developed computer codes based on our extended BAC model, denoted (16 × 16), in which the dimension of the used states basis was equal to 16. We have investigated the band gap and the spin orbit splitting as a function of Bi composition for alloys lattice matched to GaAs. We have found that the substitution of As element by N and Bi impurities leads to a significant reduction of band gap energy by roughly 198 meV/%Bi. Meanwhile, spin orbit splitting increases by 56 meV/%Bi regardless N content. There is an excellent agreement between the model predictions and experiment reported in the literature. In addition, alloys compositions and oscillator strengths of transition energies have been calculated for GaNAsBi alloys which represent active zone of temperature insensitive (1.55 μm and 1.3 μm) wavelength laser diodes intended for optical fiber communications. A crossover at about 0.6 eV has occurred between E_g and Δ_so of GaN_.039As_.893Bi_.068. When the quaternary is lattice mismatched to GaAs, resonance energy increases with Bi content if N content decreases. On the other hand, effective mass behavior of carriers at Γ point has been discussed with respect to alloy composition, k-directions and lattice mismatch.     

SiC epitaxy growth using chloride-based CVD

The growth of thick epitaxial SiC layers needed for high-voltage, high-power devices is investigated with the chloride-based chemical vapor deposition. High growth rates exceeding 100 μm/h can be obtained, however to obtain device quality epilayers adjustments of the process parameters should be carried out appropriately for the chemistry used. Two different chemistry approaches are compared: addition of hydrogen chloride to the standard precursors or using methyltrichlorosilane, a molecule that contains silicon, carbon and chlorine. Optical and electrical techniques are used to characterize the layers.     

Ab-initio calculation of band structure and linear optical properties of SbSI in para- and ferroelectric phases

An ab-initio pseudopotential calculation has been performed by using density functional methods within the local density approximation (LDA) to investigate the band structure and optical properties of the ferroelectric-semiconductor SbSI in the para- and ferroelectric phases. It has been shown that SbSI has an indirect gap in both phases (1.45 eV and 1.49 eV in the para- and ferroelectric phases respectively) and that the smallest direct gap is at the S point of the Brillouin zone (1.56 eV and 1.58 eV in the para- and ferroelectric phases respectively). Furthermore, it is shown that first-order phase transition, from the paraelectric phase to the ferroelectric phase (the transiton temperature is about 22 °C), does not change the nature of the band gap. Moreover, the linear frequency dependent dielectric function, including self-energy effects, has been calculated along the c-polar axis in the para- and ferroelectric phases.      

基于集中质量法的一维声子晶体弹性波带隙计算

通过将一维声子晶体中的原胞简化为有限多个自由度的弹簧振子结构，引入了一种基于集中 质量法的一维声子晶体弹性波带隙计算方法.与传统平面波展开法相比，该方法的计算结果 与之相符合，而且在收敛性方面较之有很大改善.通过使用集中质量法，可在得到同样计算 精度的条件下，显著降低计算量，提高计算速度. 关键词： 声子晶体 弹性波带隙 集中质量法 平面波展开法     

Position calculation of the frequency band gap in the finite photonic crystal with multiple alternations using boundary element method

In this paper, the wave transmission from finite photonic crystals with multiple alternations is investigated using boundary element method (BEM). Since that, in these structures the alternation is not in all directions of space; the investigations of the frequency band gap with desired accuracy are not practical by analytical methods. Also, the frequency dispersion of dielectric rods is an effective parameter in photonic crystals, which this effect in our calculations has been considered. Due to the high capabilities of the BEM, the transmitted wave spectrum in the photonic crystal is calculated by changing the geometrical and optical parameters of the photonic crystal and applying more alternation in its structure and the position and width of the frequency band gap is investigated. Then, it is assumed that the photonic crystal with an arbitrary angle is rotated around the axis which is perpendicular on the crystal cross section and then, it is irradiated with a plan wave. The band gap of the photonic crystals with the desired structure, desired rotation angle and multiple alternations have been solved. Very low information volume, high speed and accuracy during the calculation and useable for any desired structures are the characteristics of this method.     

Search target band gap with inverse band structure approach for complex superlattices

Because it is too difficult to pick out the needed structures from the vast possible configurations, complex superlattices have not been studied well for a long time. In this paper, an inverse band structure (IBS) approach which combined genetic algorithm search method with an empirical spds* tight-binding energy band calculation to address this problem is presented. Needed direct energy band gaps of Ga(Al)As complex superlattices are found by using this approach. It can be found that the band gap value can be same for different superlattice structures, but other properties of these complex superlattices could be different.