O掺杂MgF2电子结构和光学性质的第一性原理研究

基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了O原子不同比例(12.5％,8.33％和6.25％)掺杂MgF2晶体的几何结构、电子结构和光学性质.通过对比发现,由于O原子的掺入,体系的禁带宽度减小,材料呈现半金属性.计算也表明,O掺杂对静态介电常数和光吸收系数有重要调制作用,同时也给出了体系性质变化的...     

ZnO氧缺陷的电子结构和光学性质

采用基于密度泛函理论的平面波超软赝势方法对ZnO_0.875的电子结构和光学性质进行了计算. 用第一性原理对含氧空位的ZnO晶体进行了结构优化处理, 计算了完整的和含氧空位的ZnO晶体的电子态密度. 结合精确计算的电子态密度分析了带间跃迁占主导地位的ZnO_0.875 材料的介电函数、吸收系数、折射系数、湮灭系数和反射系数, 并对光学性质和极化之间的联系做了详细讨论. 结果表明ZnO_0.875晶体是单轴晶体, 并且在低能区域存在因氧缺陷而造成的一些特性. 我们的研究结果为ZnO的发光特性提供新的视野, 同时为ZnO的光电子材料的设计和应用提供理论基础.     

BaTiO3的电子结构和光学性质

采用第一性原理赝势平面波方法, 在局域密度近似(LDA)和广义梯度近似(GGA)下分别计算了BaTiO3立方相和四方相的电子结构, 并在局域密度近似下计算了BaTiO3立方相的光学性质. 结果表明, BaTiO3立方相和四方相都为间接带隙, 方向分别为Γ-M和Γ-X, 大小分别为2.02和2.20 eV. 对BaTiO3和PbTiO3铁电相短键上电子布居数的对比分析, 给出了它们铁电性大小的差别. 且在30 eV的能量范围内研究了BaTiO3 的介电函数、吸收系数、折射系数、湮灭系数、反射系数和能量损失系数等光学性质,并基于电子能带结构对光学性质进行了解释. 计算结果与实验数据相符合.     

高压相BeO晶体的电子结构和光学性质

应用基于密度泛函理论的第一性原理研究方法,考虑广义梯度近似(GGA)下的交换关联势,模拟计算了高压下纤维锌矿(WZ)、闪锌矿(ZB)和岩盐(RS)结构氧化铍(BeO)晶体的电子结构和光学性质等.计算结果表明,随着压力的增加,同种结构下原子间的键长和电荷转移有所减小,并且价带和导带分别向低能和高能方向移动,禁带展宽.与常压下的BeO相比,随着压力的增加,三种结构的BeO晶体的光学性质有一定的变化,介电函数、吸收系数、折射率以及电子能量损失谱曲线出现更多的精细结构,峰的数量增多;各高压相结构的吸收谱和能量损失谱宽度逐次展宽;吸收系数曲线的吸收峰及其位于低能区域的吸收边以及电子能量损失谱峰的位置均发生一定程度的蓝移.     

天然杂质对闪锌矿电子结构和半导体性质的影响

采用密度泛函理论系统研究了分别含有十四种天然杂质的闪锌矿的电子结构,并讨论了这十四种杂质对闪锌矿半导体性质的影响.研究结果表明,锰、铁、钴、镍、铜、镉、汞、银、铅、锑杂质的存在使闪锌矿的带隙变窄,导致吸收带边增大.除了镉和汞杂质外,其余杂质的存在均导致费米能级向高能级方向移动,并且在闪锌矿禁带中产生了杂质能级.铁、镓、锗、铟、锡、锑杂质使闪锌矿的半导体类型由p型变为n型;而锰、钴、镍、铜、镉、汞、银、铅杂质对闪锌矿的半导体类型没有影响.铜杂质使闪锌矿由直接带隙变为间接带隙半导体.     

NbC固体表面能带和电子结构的理论研究

采用DFT/BLYP方法对NbC(001)和(111)面的电子结构进行研究。计算结果表明,对于NbC(001)表面,其表面态主要集中于费米能级(EF)下方约4.5eV附近区域,并以表面Nb原子和C原子为主要成分。O2分子在该表面吸附时,趋向于吸附在表面Nb原子上。对于NbC(111)表面,其表面态集中在EF下方0.02.0eV区域,靠近EF的态具有较高的表面活性,其主要成分为表面Nb原子的4dxz/dyz成分。上述结论与光电子能谱实验结果基本一致;但由于金属原子d电子数的差异导致NbC(111)表面态成分与类似的TiC化合物并不相同。     

SnO2(110)弛豫表面构型与电子结构的第一性原理研究

采用基于第一性原理的密度泛函方法对SnO₂(110)表面的构型和电子结构进行了系统研究. 结果表明, 与理想表面相比, 表面弛豫导致表层五配位Sn原子向体相方向位移, 六配位Sn原子以及表面氧原子往真空方向移动, 而桥氧原子位置基本保持不变. 当表面厚度小于3 nm时, 表面能和表层原子的弛豫大小随着层数的增加出现振荡现象. 由能带计算结果得知, 以桥氧的2p_y/2i>p_z轨道为主要成分的能带出现在体相的带隙中. 进一步考察了弛豫对表面电子结构的影响.     

有机晶体材料DAST和DSTMS的电子结构与光学性质

采用基于赝势平面波基组的密度泛函理论(DFT)方法,研究了有机晶体材料4-(4-二甲氨基苯乙烯基)甲基吡啶对甲苯磺酸盐(DAST)和4-(4-二甲氨基苯乙烯基)甲基吡啶2,4,6-三甲基苯磺酸盐(DSTMS)的电子结构和光学性质.结果表明,两种化合物具有相似的能带结构,其中价带顶和导带底分别含有较多二甲氨基和甲基吡啶中N原子的2p轨道成分.在线性光学性质方面,两种化合物具有较高的双折射率(Δn>0.5),在中远红外区均具有较好的透过性能.在二阶非线性光学性质方面,该类晶体具有较强的二阶倍频(SHG)效应,静态倍频系数d11约为150 pm V-1.由能带结构分析结果可知,体系的SHG效应与推拉电子基团之间的电荷转移密切相关,同时乙烯桥键在该电子转移过程中也起着重要作用.     

吲哚咔唑异构体的电子结构和光学性质

分别采用密度泛函理论(DFT)和单激发组态相互作用(CIS),在6-31G(d,p)基组水平上优化了5个吲哚咔唑分子的基态和激发态结构.在此结构的基础上,用含时密度泛函理论(TD-DFT)在相同基组水平和极化连续介质模型(PCM)下计算了模型分子的吸收和发射光谱.这几个吲哚咔唑异构体的发射光谱有明显的差别,如异构体5([3,2-b]型)有较大的振子强度,但是相对于其他异构体,其发射能量最小;异构体4([3,2-a]型)的发射能量最大;异构体2([2,3-b]型)的最大振子强度在250-450 nm范围内,与其他几个分子相比为最小.这主要是由分子的激发态几何变化和轨道能级的不同导致的.本文还考察了这类分子的一阶超极化率,结果显示5个分子极化率在同一水平,但静态第一超极化率(β0)有明显差别,异构体2的β0值最大.     

椅型碳纳米管吸附氢原子电子结构的密度泛函研究

采用密度泛函方法对氢原子在(5,5)椅型碳纳米管上的吸附进行了研究, 分别考察了氢原子覆盖度为5%和10%时的构型和吸附能. 研究结果表明, H原子吸附在管外壁要比管内壁能量上更为有利, 同时第二个H原子倾向于吸附在前一个H原子的吸附位置邻近的碳原子上. 由能带计算结果得知, 吸附一个H原子时, 椅型碳纳米管将由导体转变为半导体; 当第二个H原子处在偶数位时, 纳米管仍保持较好的导电性能, 而吸附在奇数位时将使管的传输能力减弱. 本文进一步通过分析纳米管(共轭体系的分布情况对管传输性质的变化进行解释.     

Ab initio Study of Electronic Structure and Properties of Crystalline of 1,5-Diamino-1,2,3,4-tetrazole

Density functional method was applied to study 1,5‐diamino‐1,2,3,4‐tetrazole (DAT, CH₄N₆) in both gaseous and bulk states. The banding and electronic structures of crystalline have been investigated at DFT‐B3LYP/ 6‐311G** level of theory. Relaxed crystal structure compares well with experimental data. The light fluctuation of the frontier orbital, which is mainly formed by atomic orbital of N(4) (heterocycle), is the most reactive part of the molecule, which is in good agreement with the experimental results. The energy gap is 9.035 eV, which indicates that DAT is an insulator. The distribution of electrostatic potential is uniform, indicating DAT is insensitive. The charge density of the intermolecular regions in the plane is not overlaid, indicating that the intermolecular interaction between the neighboring molecules along this direction in the bulk is very weak. The overlap populations of N(1)? N(2) bonds are much less than those of other bonds, therefore the N(1)? N(2) bonds first rupture by external stimuli.     

聚吡咯并[3,4-c]吡咯的电子结构及导电性研究

采用密度泛函(DFT)方法在6-31g(d)水平下研究了聚吡咯和聚吡咯并[3,4-c]吡咯, 以及它们的单体和低聚物的电子结构. 对中心键的键长、电荷密度以及Weberg键级的研究表明, 随着主链聚合度的增加, 其共轭性增强. 对聚合物还进行了能带结构和态密度分析. 结果发现, 在3位聚合的并环化合物具有最优的导电性能, 其能隙仅有0.25 eV, 可以作为潜在的导电聚合物材料.     

Crystal Structure, Energy Band and Optical Properties of Phosphate In（PO3）3

1 INTRODUCTION stand the chemical bonding properties and electronic origins of optical transition for solid In(PO3)3, the During the past decades, many indium phosphates crystal energy band and optical response functions have been reported and researched on their conduc- are also calculated. tivity anisotropy, band structure and optical proper- ties[1, . However, to our current knowledge, the com- 2] 2 EXPERIMENTALAND pounds containing alkaline-earth metals are rarely COMPUTATIO…     

C_(36)聚合体电子结构的理论研究

采用PM3 和DFT/B3LYP方法对2D六方网状,以及1D链状C36聚合体的构型进行全优化,探讨了其电子结构和稳定性;并在从头算水平上计算了相应的能带结构。研究发现,C36形成聚合体后构型发生了显著变化; 与0D 的结构比较,C36聚合为1D或2D结构后,笼内CC键长变化明显。计算表明C36聚合后稳定性提高,呈半导体或绝缘体性质。聚合后C36内部CC键定域化程度的增强是其稳定性提高的主要因素。     

Ab initio Study of Electronic Structure and Properties in Crystalline 1,1,3,3,5,5‐Hexaazidocyclotriphosphazene

The banding and electronic structures of crystalline 1,1,3,3,5,5‐hexaazidocyclotriphosphazene (P₃N₂₁) have been investigated at DFT‐B3LYP/6‐31G(d) level. Relaxed crystal structure compares well with experimental data. The energy gap is 5.57 eV, indicating that P₃N₂₁ is an insulator. The frontier orbital is mainly formed by atomic orbitals of azido group, so it is the most reactive part of the molecule. The intermolecular interaction is strong along the direction that is nearly perpendicular to the phosphazene ring. The distribution of electrostatic potential is quite uneven, so P₃N₂₁ has a very high impact sensitivity. The point charge electrostatic potential is very high between the azido groups of the neighboring molecules, which indicates that the crystal lattice in this position may easily be broken and becomes the explosion center when P₃N₂₁ is impacted. The overlap populations of P–N_α bonds are much less than those of other bonds, therefore the P–N_α bonds first rupture by external stimuli, which agrees well with the experimental study of mass spectrum.     

Effect of Zr and C Co-doping on the Optical Properties and Electronic Structure of TiO_2

The systematic trends and effect introduced by Zr and C co-doping to TiO2 of electronic structure and optical properties of anatase TiO2 have been calculated by the plane-wave ultra-soft pseudopotential density functional theory (DFT) method within the generalized gradient approximation (GGA) for the exchange-correlation potential. Through the current calculations, the density of states (DOS), energy band structure and optical absorption coefficients have been obtained for TiO2 and compared with the doped TiO2, and the influence of electronic structure and optical properties caused by Zr and C co-doping has been presented qualitatively together. The results revealed that the energy band gap has been decreased owing to the doped Zr and C, whereas the optical absorption coefficients have been increased in the region of 400～800 nm and a red shift of absorption band can be found. Accordingly, photo catalytic activity of TiO2 has been enhanced. The current calculations are in good agreement with the experimental data.     

Preparation,Crystal Structure,Physical Properties,and Electronic Band Structure of TlTaS3

TlTaS₃ was prepared by applying a sequence of two melting processes with mixtures of Tl₂S, Ta, and S having different molar metal to sulphur ratios. TlTaS₃ crystallises in space group Pnma with a = 9.228(3)Å, b = 3.5030(6)Å, c = 14.209(3)Å, V = 459.3(2)ų, Z = 4. The structure is closely related to the NH₄CdCl₃‐type. Characteristic features of the structure are chains of edge‐sharing [Ta(+5)S₄S_2/2]₂ double octahedra running along [010]. These columns are linked by Tl⁺ ions. The Tl⁺ ion is surrounded by eight S^2— anions to form a distorted bi‐capped trigonal prism. The Tl⁺ ions are shifted from the centre of the trigonal prism toward one of the rectangular faces. This is discussed in context with other isostructural compounds. TlTaS₃ is a semiconductor. The electronic structure is discussed on the base of band structure calculations performed within the framework of density functional theory.     

CO分子结点电子结构和输运性质的第一原理研究

采用基于密度泛函理论(DFT)的非平衡态格林函数方法(NEGF), 计算了CO分子结点低偏压下的电流和电导. 通过系统透射谱、投影态密度(PDOS)以及分子自洽投影哈密顿量(MPSH)本征态的分析将透射通道与局域分子轨道联系起来, 从系统电子结构解释了其传输性质. 讨论了电荷转移对系统电导的影响.     

Growth, Band Structure and Optical Properties of LiSrBO3 Crystal

The bulk crystal of LiSrBO3 (8.39 g) with a size of 21mm×20mm×15mm was grown by high temperature solution growth method. The relationship between growth habit and crystal structure was discussed. The transmission spectrum shows an UV absorption edge at about 300 nm. The melting temperature of this crystal was determined to be 942 ℃ by DTA-TG measurement. The band structure of the LiSrBO3 crystal was studied by means of the first principle method. An indirect band gap was found to be about 4.0 eV,and a low dielectric constant was estimated to be about 1.9 in terms of theoretical results.