采用第一性原理研究非金属掺杂BiOCl的电子结构和光吸收性质

基于密度泛函理论的第一性原理分别研究了不同浓度Br和I掺杂BiOCl体系的能带结构、态密度、形成能和光学性质.研究结果表明,由于Br的4p和I的5p轨道作用,Br和I掺杂可在一定程度上降低BiOCl的禁带宽度,拓宽BiOCl的光吸收范围.Br和I掺杂BiOCl的形成能计算结果表明,Br掺杂BiOCl的稳定性高于I掺杂体系.对于B,C,N,Si,P和S掺杂BiOCl体系,掺杂能级的形成主要由掺杂元素的np轨道贡献,使BiOCl吸收带边红移至可见光区.而S掺杂则位于价带顶位置,有效地降低了BiOCl禁带宽度,使BiOCl响应波长出现红移,且未形成中间能级,不易成为俘获陷阱,因此S掺杂将是一种提高BiOCl可见光光催化活性的改性方法.     

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.     

钛铁矿型六方相ZnTiO3的电子结构和光学性质

分别采用基于密度泛函理论(DFT)的局域密度近似(LDA)和广义梯度近似(GGA)方法对钛铁矿型六方相ZnTiO₃的电子结构进行了第一性原理计算, 并在局域密度近似下计算了六方相ZnTiO₃的光学性质, 并将计算结果与实验数据进行了对比. 结果表明, 在局域密度近似下计算得到的结构参数更接近实验数据. 理论预测六方相ZnTiO₃属于直接带隙半导体材料, 其禁带宽度(布里渊区Z 点)为3.11 eV. 电子态密度和Mulliken 电荷布居分析表明Zn―O键是典型的离子键而Ti―O键是类似于钙钛矿型ATiO₃ (A=Sr, Pb, Ba)的Ti―O共价键. 在50 eV的能量范围内研究了ZnTiO₃的介电函数、吸收光谱和折射率等光学性质, 并基于电子能带结构和态密度对光学性质进行了解释.     

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.     

聚偏二氟乙烯晶体的电子结构和光学性质

利用含Tkatchenko-Scheffler(TS)色散修正的密度泛函理论的第一性原理方法对九种聚偏二氟乙烯(PVDF)晶相的电子结构和光学性质进行了计算. 结果表明,PVDF晶体作为一种绝缘体,能带具有密集且平直等特征,其带隙值在6.05-7.34 eV之间,且和实验值接近. 价带主要是F原子的2s和2p态起主要贡献,导带主要由C原子的2p态和H原子的1s态共同参与构成. 在0-35 eV光子能量范围内,介电函数、吸收率、反射率和折射率等光学性质发生变化主要在深紫外区域. 根据介电函数等光学参数的谱特点,可以将九种PVDF的晶相划分为{Ⅰ_p},{Ⅱ_pu},{Ⅱ_au,Ⅱ_ad,Ⅱ_pd,Ⅲ_pu},{Ⅲ_au,Ⅲ_ad,Ⅲ_pd}等四类,每一类都具有相似的光学参数特点.     

Effect of Pressure on Electronic Structures and Optical Properties of Rocksalt InN

The electronic structures and optical properties of rocksalt indium nitride (InN) under pres-sure were studied using the first-principles calculation by considering the exchange and cor-relation potentials with the generalized gradient approximation. The calculated lattice con-stant shows good agreement with the experimental value. It is interestingly found that the band gap energy E_g at the Γ or X point remarkably increases with increasing pressure, but E_g at the L point does not increase obviously. The pressure coefficient of E_g is calculated to be 44 meV/GPa at the Γ point. Moreover, the optical properties of rocksalt InN were calculated and discussed based on the calculated band structures and electronic density of states.     

硼、铝和镓掺杂对硅纳米管电子结构和光电性质的影响

基于密度泛函理论的第一性原理计算,研究了本征硅纳米管（SiNTs）的几何结构,以及Ⅲ族元素B、Al、Ga掺杂对单壁锯齿型（14,0）SiNTs稳定性、电子结构和光学性质的影响。结果表明,褶皱型SiNTs为SiNTs稳定存在的结构,B、Al、Ga掺杂能够提高SiNTs的稳定性。本征（14,0）SiNTs属于窄带隙金属材料,通过B、Al、Ga的分别掺杂,SiNTs的带隙变宽,实现了SiNTs从金属性向半导体性质的转变。随着Ⅲ族元素原子序数的增大,其掺杂体系的稳定性不断降低,相应的带隙也不断减少。B、Al、Ga掺杂的单壁锯齿型（14,0）SiNTs具有近乎一致的光学性质,对于紫外光有着很强的吸收特性,并且对于红外和可见光吸收也有着不错的提升。     

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.     

The Electronic and Optical Properties of Au Doped Single-Layer Phosphorene

The electronic properties and optical properties of single and double Au-doped phosphorene have been comparatively investigated using the first-principles plane-wave pseudopotential method based on density functional theory. The decrease from direct band gap 0.78 eV to indirect band gap 0.22 and 0.11 eV are observed in the single and double Au-doped phosphorene, respectively. The red shifts of absorbing edge occur in both doped systems, which consequently enhance the absorbing of infrared light in phosphorene. Band gap engineering can, therefore, be used to directly tune the optical absorption of phosphorene system by substitutional Au doping.     

Electronic and Optical Properties of O-Terminated Armchair Graphene Nanoribbons

The structure, electromagnetic and optical properties of the O-terminated graphene nanorib-bons with armchair edge are studied using first-principles theory. The results show that the O-terminated armchair edge are more stable than the H-terminated ribbons and show metal-lic character. Spin-polarized calculations reveal that the antiferromagnetic state are more stable than the ferromagnetic state. The energy band and density of states analyses show that the O-terminated armchair edge are antiferromagnetic semiconductors. Because of the terminated O atoms, the dielectric function has an evident red shift and the first peak is the strongest with its main contribution derived from the highest valence band. The peaks of the dielectric function, re ection, absorption, energy loss are related to the transition of electrons. Our results suggest that the O-terminated graphene nanoribbons have potential applications in nanoelectronics, opto-electric devices.     

Cu掺杂MgF2晶体的电子结构及光学特性

基于密度泛函理论(DFT)的第一性原理平面波超软赝势方法,计算了纯的MgF2晶体和掺杂不同原子分数(2.08%,4.16%,6.24%)Cu的MgF2晶体结构、电学性质以及光学性质.结果表明:Cu的掺入导致MgF2晶体禁带宽度逐渐变窄,并且Cu掺杂使得MgF2晶体折射率和吸收峰增加,特别是在4eV附近区域出现了新吸收峰.同时也给出了引起体系性质变化的物理机制,Cu掺杂MgF2晶体在光电化学方面有着潜在的应用价值.     

黄铜矿型铜基硫属半导体材料的电子结构和光学性质

采用基于赝势平面波基组的密度泛函理论方法, 对具有黄铜矿结构的6种CuXY₂(X=Ga, In; Y=S, Se, Te)晶体的构型、 电子结构、 线性及二阶非线性光学性质进行了研究. 结果表明, 6种CuXY₂均为直接带隙半导体, 具有相似的能带结构. 当X原子相同时, 随着Y原子按S→Se→Te依次改变时, 体系的静态介电常数、 静态折射率和静态倍频系数(d₃₆)依次递增. 在占据带中, 位于价带顶附近的能带对体系倍频效应影响最为显著, 该系列化合物的能带主要成分为Cu的3d轨道和Y原子价层p轨道; 对于空能带, 对倍频系数影响较大的是以X原子价层p轨道为主要成分的能带. 6种晶体中, CuInSe₂晶体具有较高的光电导率并对太阳光具有较好的吸收性能. 综合考虑体系的双折射率和倍频效应等因素, CuGaS₂和CuGaSe₂ 2种晶体在二阶非线性光学领域具有潜在的应用价值.     

Electronic Structure and Optical Properties of K2Ti6O13 Doped with Transition Metal Fe or Ag

Based on the experimental study of the optical properties of K₂Ti₆O₁₃ doped with Fe or Ag, their electronic structures and optical properties are studied by the first-principles method based on the density functional theory (DFT). The calculated optical properties are consistent with the experiment results. K₂Ti₆O₁₃ doped with substitutional Fe or Ag has isolated impurity bands mainly stemming from the hybridization by the Fe 3d states or Ag 4d states with Ti 3d states and O 2p states and the band gap becomes narrower, the absorption edge of K₂Ti₆O₁₃ thus has a clear red shift and the absorption of visible light can be realized after doping. For Fe-doped K₂Ti₆O₁₃, the impurity bands are in the middle of the band gap, suggesting that they can be used as a bridge for valence band electrons transition to the conduction band. For Ag-doped K₂Ti₆O₁₃, the impurity bands form a shallow acceptor above the valence band and can reduce the recombination rate of photoexcited carriers. The experimental and calculated results are significant for the development of K₂Ti₆O₁₃ materials that have absorption under visible light.     

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.     

含有Pt―Pt键金属配合物的电子结构和二阶非线性光学性质

采用量子化学密度泛函理论(DFT)结合有限场(FF)的方法对一系列含有Pt―Pt键金属配合物的电子结构和二阶非线性光学(NLO)性质进行了理论计算. 结果表明改变共轭配体对Pt―Pt键影响不大. 由配体到Pt―Pt金属基团的电荷转移强度随配体增长而变大. 金属配合物静态一阶超极化率随配体的增长而增大, 配合物电荷的改变基本不影响这类化合物的二阶NLO性质. 具有相对长的共轭配体的配合物IId具有最大的二阶NLO响应. 含时密度泛函理论(TD-DFT)计算表明配合物IId的二阶NLO响应来自于混有配体到金属的配体内的π→π^*电荷转移跃迁的贡献.     

C60异噁唑环衍生物的结构、电子光谱和非线性光学性质的研究

The AM1 semiempirical calculation method was employed to study the structures and electronic properties of a series of isoxazolo fullerene derivatives. Based on the AM1 geometry optimization, the electronic spectra of molecules were studied by using ZINDO/CIS methods. The results indicated the HOMO LUMO energy gaps of those isoxazolo fullerenes were lower than that of C60. There existed the intramolecular electron transfer from the additional section to C60 moiety. The electronic spectrum data showed that the exception of the absorption was beyond 400 nm.The results were in good accordance with the experiment results. Nonlinear optical susceptibilities α, β and γ of molecules were calculated according to Finite Field(FF)/AM1, and the influence of molecular structures on nonlinear optical properties was examined.     

Y-Cu共掺杂ZnO电子结构与光学性质的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理平面波赝势法研究了本征ZnO、Y和Cu单掺杂ZnO、Y-Cu共掺杂ZnO的电子结构和光学性质. 计算结果表明, 在本文的掺杂浓度下, Y和Cu单掺杂可以提高ZnO的载流子浓度, 从而改善ZnO的导电性, Y-Cu共掺时ZnO半导体进入简并状态, 呈现金属性. Y 掺杂ZnO可以提高体系在紫外区域的吸收, 而Cu掺杂ZnO在可见光和近紫外区域发生吸收增强现象, 其中由于Y离子和Cu离子之间的协同效应, Y-Cu共掺杂ZnO时体系对可见光和近紫外区域的光子能量吸收大幅增加, 因此Y-Cu共掺杂ZnO可以用于制作光电感应器件.     

黄铜矿型半导体材料CuAlX2 (X=S,Se, Te)的电子结构和光学性质

采用基于赝势平面波基组的密度泛函理论方法,研究具有黄铜矿结构的CuAlX2(X=S,Se,Te)晶体的电子结构,并预测了它们的线性和非线性光学性质.结果表明:这些化合物具有相似的能带结构,带隙随X原子从S→Se→Te依次减小.三种晶体的静态介电常数、静态折射率和静态倍频系数d36的变化情况与带隙的变化相反,随着X原子自S→Se→Te改变依次递增,但静态双折射率依次递减.该系列化合物的倍频效应主要来源于价带顶附近的占据能带向以Al和X原子的p电子态为主要成分的空带之间的跃迁.在三种晶体中,CuAlTe2除静态双折射率偏小外,其它光学性能要优于CuAlS2和CuAlSe2.     

Structures and Electromagnetic Properties of Boron Nitride Nanoribbons Doped with Transition Metals

Inspired by the recent discovery of the Ti-doped BN nanocages, here we report the design of novel boron nitride (BN) nanoribbons (BNNRs) doped with fourth-row transition metals (Sc−Cu) and the prediction of their structural and electromagnetic properties. First-principles calculations and ab initio molecular dynamics simulations show that Ti-doped BNNR possesses both thermodynamic and kinetic stability at high temperatures for synthesis of BN materials. Metal doping may make the nonmagnetic pristine BNNR ferromagnetic or antiferromagnetic, depending on the metal. The doping with all considered metals reduces substantially the band gap of pristine BNNR. For example, Sc-doped BNNR is ferromagnetic with an indirect band gap of 1.18 eV, while V-doped nanoribbon is antiferromagnetic with a direct gap of 2.50 eV. Remarkably, the carrier mobility in both materials is significantly enhanced compared to the pristine BNNR. Our findings suggest that doping with different metals may endow BNNRs with versatile electronic and magnetic properties.     

Effect of Ultrasonication on Optical Properties and Electronic States of Conjugated Polymer MEH-PPV

Poly[2-methoxy-5-（2＇-ethyl-hexyloxy）-1,4-phenylene vinylene]（MEH-PPV）solutions with different concen-trations were prepared in chloroform for different ultrasonication times.The ultraviolet absorption and photoluminescence（PL）spectra of the MEH-PPV solutions were measured,and the electronic states of the polymer chains under different experimental conditions were studied.The results showed that the effects of ultrasonication on the dilute and concentrated solutions were different.After ultrasonication,the intensity of the absorption peak at 280 nm significantly decreased,relative to the absorption peak at 500 nm for both dilute and concentrated solutions,indicating that the proportion of the two excited states in the polymer chains had changed.For dilute MEH-PPV solutions,the blue-shifted absorption（at about 500 nm）and PL spectra show that ultrasonication also led to polymer chain degradation and thus shortened the effective conjugation length.For concentrated solutions,however,the peak positions of the absorption spectra remained unchanged.In addition,the effects of the solution temperatures on the optical spectra for the MEH-PPV solutions were also discussed.