层数调控磷烯能带与光学性质的研究

近年来,黑磷作为兼具石墨烯和过渡金属硫化物之长的新型二维材料而倍受关注.本文基于密度泛函理论,研究了不同厚度黑磷的电子结构与光学性质.结果表明,黑磷的性质与其厚度密切相关,可通过厚度调整实现能带与光学性质的可调控性.层间相互作用导致费米能级附近价带和导带的劈裂,是造成黑磷带隙随层数减小的根本原因.黒磷的静态折射率和静态反射率的大小均随层数的增大有增大的趋势,并且各层黑磷的反射峰均位于紫外光波段.黑磷对光的吸收涵盖了可见光到紫外光区域,对光的损失范围小于4eV.本文基于能带图和分波态密度图,从电子跃迁的角度分析了黑磷各项光学性质的变化情况,旨在为黑磷的带隙及光学性质层数可调控性提供理论依据.     

First-principles study of the electronic structure and optical properties of cubic Perovskite NaMgF_3

The structural, electronic, and optical properties of cubic perovskite NaMgF3 are calculated by plane-wave pseudopo- tential density functional theory. The calculated lattice constant a0, bulk modulus B0, and the derivative of bulk modulus B~ are 3.872/~, 78.2 GPa, and 3.97, respectively. The results are in good agreement with the available experimental and theo- retical values. The electronic structure shows that cubic NaMgF3 is an indirect insulator with a wide forbidden band gap of Eg = 5.90 eV. The contribution of the different bands is analyzed by total and partial density of states curves. Population analysis of NaMgF3 indicates that there is strong ionic bonding in the MgF2 unit, and a mixture of ionic and weak covalent bonding in the NaF unit. Calculations of dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, optical reflectivity, and conductivity are also performed in the energy range 0 to 70 eV.     

Al，Ga掺杂ZnO电子结构和光电特性的第一性原理计算

采用基于密度泛函理论(DFT)框架下广义梯度近似(GGA)的PBE平面波超软赝势方法,计算了本征ZnO,Al掺杂ZnO(ZnAlO)和Ga掺杂ZnO(ZnGaO)的能带结构、态密度、复介电函数和复电导率. 其中Al或Ga是以替位杂质的形式进入ZnO晶格. 计算结果表明纤锌矿型ZnO,ZnAlO和ZnGaO都是直接带隙半导体材料,掺杂后ZnO的带隙变小,且ZnAlO的带隙略大于ZnGaO. 掺杂后ZnO的电子结构发生变化,费米能级由本征态时位于价带顶上移进入导带,ZnO表现为n型掺杂半导体材料,掺杂后在导带底出现大量由掺杂原子贡献的自由载流子—电子,明显提高了电导率和介电函数,改善了ZnO的导电性能,并且ZnAlO的导电性能要略好于ZnGaO.     

Al，Ga掺杂ZnO电子结构和光电特性的第一性原理计算

采用基于密度泛函理论(DFT)框架下广义梯度近似(GGA)的PBE平面波超软赝势方法,计算了本征ZnO,Al掺杂ZnO(ZnAlO)和Ga掺杂ZnO(ZnGaO)的能带结构、态密度、复介电函数和复电导率. 其中Al或Ga是以替位杂质的形式进入ZnO晶格. 计算结果表明纤锌矿型ZnO,ZnAlO和ZnGaO都是直接带隙半导体材料,掺杂后ZnO的带隙变小,且ZnAlO的带隙略大于ZnGaO. 掺杂后ZnO的电子结构发生变化,费米能级由本征态时位于价带顶上移进入导带,ZnO表现为n型掺杂半导体材料,掺杂后在导带底出现大量由掺杂原子贡献的自由载流子—电子,明显提高了电导率和介电函数,改善了ZnO的导电性能,并且ZnAlO的导电性能要略好于ZnGaO.     

Structural,electronic and optical properties of cubic SrTiO3 and KTaO3: Ab initio and GW calculations

We present first-principles VASP calculations of the structural, electronic, vibrational, and optical properties of paraelectric SrTiO₃ and KTaO₃. The ab initio calculations are performed in the framework of density functional theory with different exchange-correlation potentials. Our calculated lattice parameters, elastic constants, and vibrational frequencies are found to be in good agreement with the available experimental values. Then, the bandstructures are calculated with the GW approximation, and the corresponding band gap is used to obtain the optical properties of SrTiO₃ and KTaO₃.     

第一性原理研究Be-S共掺杂AlN纳米片的电子结构和光学性质

基于密度泛函理论体系下广义梯度近似(GGA),利用第一性原理方法计算了Be替代Al、S替代N和Be-S共掺杂对氮化铝纳米片的电子结构和光学性质的影响.计算结果表明,掺杂改变了氮化铝纳米片的带隙,但仍显示半导体特性. Be掺杂类型对氮化铝纳米片的晶体结构影响不大,而S掺杂和Be-S共掺杂都使得氮化铝纳米片有不同程度的弯曲.同时Be-S共掺杂中S原子起到激活受主杂质Be原子的作用,使得受主能级向低能方向移动.共掺杂比单掺杂具有更高的受主原子浓度,并减小局域化程度.光学性质也发生较大改变:S原子掺杂氮化铝纳米片的介电函数虚部出现第二介电峰,Be掺杂和Be-S共掺杂使得损失谱的能量区间有所展宽,峰值降低并向高能区移动.     

First-principles study of structural,electronic and optical properties of ZnF_2

The structural, electronic, and optical properties of rutile-, CaC12-, and PdF2-ZnF2 are calculated by the plane-wave pseudopotential method within the density functional theory. The calculated equilibrium lattice constants are in reasonable agreement with the available experimental and other calculated results. The band structures show that the rutile-, CaCl2-, and PdF2-ZnF2 are all direct band insulator. The band gaps are 3.63, 3.62, and 3.36 eV, respectively. The contribution of the different bands was analyzed by the density of states. The Mulliken population analysis is performed. A mixture of covalent and weak ionic chemical bonding exists in ZnF2. Furthermore, in order to understand the optical properties of ZnF2, the dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy, and optical reflectivity are also performed in the energy range from 0 to 30 eV. It is found that the main absorption parts locate in the UV region for ZnF2. This is the first quantitative theoretical prediction of the electronic and optical properties of ZnF2 compound, and it still awaits experimental confirmation.     

Ag,Zn掺杂对CdS电子结构和光学性质的影响

运用密度泛函平面波赝势方法和广义梯度近似, 对替代式掺杂Ag和Zn的闪锌矿CdS的超晶胞晶体结构、电子结构和光学性质进行了计算, 分析了其电子态分布与结构的关系,给出了掺杂前后CdS体系的介电函数和复折射率函数. 研究表明,掺有Ag的CdS晶体空穴浓度增大,会明显提高材料的电导率, 而Zn掺杂不改变CdS晶体载流子浓度; Ag, Zn掺杂体系光学带隙均变窄; 通过分析掺杂前后CdS晶体的介电函数和复折射率函数,解释了体系的发光机理. 关键词： 密度泛函理论 Ag,Zn掺杂CdS 电子结构 光学性质     

Electronic and optical properties of pure and Ce3+-doped CaS single crystals: a first-principles prediction

This paper investigates the electronic and optical properties for pure and Ce 3+-doped CaS crystals by using the first-principles total energy calculations.The results show that CaS:Ce has a direct band gap of 2.16 eV,and the top of the valence band is determined by S 3p states and the bottom of the conduction band is determined by Ce 4f states,respectively.Our results validate that the yellow emission from CaS:Ce is produced by doped cerium and the green emission quenches at 12.5% cerium concentration.The Ce-S bond shows more covalent character than the Ca-S bond.     

Electronic and optical properties of the zinc-blende structured LiZnN under pressure

The electronic and optical properties of the cubic zinc-blende (ZB) structured filled tetrahedral semiconductor α-LiZnN under pressure are investigated by using \textit{ab initio} plane wave pseudopotential density functional theory method within the generalized gradient approximation (GGA). The electronic band structure and the density of state under pressure are systematically described. The basic optical constants, including the reflection and absorption spectra, the energy-loss function, the complex refractive index and the dielectric function, are calculated and analysed at different external pressures. Our results suggested that the ZB α-LiZnN is transparent in the partially ultra-violet to the visible light region, and it seems that the transparency is hardly affected by the pressure.     

First-principles study of the electronic and optical properties of ZnO nanowires

The geometric, energetic, electronic structures and optical properties of ZnO nanowires (NWs) with hexagonal cross sections are investigated by using the first-principles calculation of plane wave ultra-soft pseudo-potential technology based on the density functional theory (DFT). The calculated results reveal that the initial Zn-O double layers merge into single layers after structural relaxations, the band gap and binding energies decrease with the increase of the ZnO nanowire size. Those properties show great dimension and size dependence. It is also found that the dielectric functions of ZnO NWs have different peaks with respect to light polarization, and the peaks of ZnO NWs exhibit a significant blueshift in comparison with those of bulk ZnO. Our results gives some reference to the thorough understanding of optical properties of ZnO, and also enables more precise monitoring and controlling during the growth of ZnO materials to be possible.     

Theoretical investigation of structural and optical properties of semi-fluorinated bilayer graphene

We have studied the structural and optical properties of semi-fluorinated bilayer graphene using density functional theory. When the interlayer distance is 1.62 , the two graphene layers in AA stacking can form strong chemical bonds.Under an in-plane stress of 6.8 GPa, this semi-fluorinated bilayer graphene becomes the energy minimum. Our calculations indicate that the semi-fluorinated bilayer graphene with the AA stacking sequence and rectangular fluorinated configuration is a nonmagnetic semiconductor(direct gap of 3.46 e V). The electronic behavior at the vicinity of the Fermi level is mainly contributed by the p electrons of carbon atoms forming C=C double bonds. We compare the optical properties of the semifluorinated bilayer graphene with those of bilayer graphene stacked in the AA sequence and find that the semi-fluorinated bilayer graphene is anisotropic for the polarization vector on the basal plane of graphene and a red shift occurs in the [010]polarization, which makes the peak at the low-frequency region located within visible light. This investigation is useful to design polarization-dependence optoelectronic devices.     

萤石结构TiO2的电子结构和光学性质

利用第一性原理计算了立方相萤石TiO₂的晶胞参数，能带结构和电子态密度.结果显示萤石TiO₂属于间接带隙半导体材料，其间接禁带宽度(Γ→X)E_g为2.07eV，比常见的金红石和锐钛矿TiO₂的禁带宽度窄.为了更清楚地了解萤石的光学性质，利用Kramers-Kronig色散关系，分别对萤石和金红石TiO₂的复介电常数、吸收率等参数进行了计算，并将二者结果做了     

萤石结构TiO2的电子结构和光学性质

利用第一性原理计算了立方相萤石TiO₂的晶胞参数,能带结构和电子态密度.结果显示萤石TiO₂属于间接带隙半导体材料,其间接禁带宽度(Γ→X)E_g为2.07eV,比常见的金红石和锐钛矿TiO₂的禁带宽度窄.为了更清楚地了解萤石的光学性质,利用Kramers-Kronig色散关系,分别对萤石和金红石TiO₂的复介电常数、吸收率等参数进行了计算,并将二者结果做了 关键词： 2')" href="#">萤石结构TiO₂ 密度泛函理论 能带结构 光学性质     

用密度泛函理论研究氮化硅新相的电子结构、光学性质和相变

运用第一性原理赝势方法,对氮化硅新相(六方Pˉ6和Pˉ6′相)的电子结构、光学性质和相变过程进行分析,研究能带结构、介电函数谱、反射谱和能量损失函数的变化机理.研究发现,β→Pˉ6→δ相变是可行的,在室温下β→Pˉ6和Pˉ6→δ相变的临界压强分别为42.9和47.7 GPa;相界的斜率为正值表明Pˉ6→δ相变过程伴随着晶胞体积的塌缩;Pˉ6和Pˉ6′相分别属于直接带隙和间接带隙半导体,能隙宽度分别为4.98和4.01 eV;得到了两相的零频介电常数;反射谱表明,两相的强反射峰均位于真空紫外线区域,因此可以用作紫外光屏蔽或紫外探测材料;在可见光区域,两相表现为近似透明.     

Structural, electronic, and optical properties of ZnOl_xSex alloys using first-principles calculations

The structural, electronic, and optical properties of binary ZnO, ZnSe compounds, and their ternary ZnOl_xSex alloys are computed using the accurate full potential linearized augmented plane wave plus local orbital （FP-LAPW ＋ lo） method in the rocksalt （B 1） and zincblende （B3） crystallographic phases. The electronic band structures, fundamental energy band gaps, and densities of states for ZnO1_xSex are evaluated in the range 0 〈 x 〈 1 using Wu-Cohen （WC） generalized gradient approximation （GGA） for the exchange-correlation potential. Our calculated results of lattice parameters and bulk modulus reveal a nonlinear variation for pseudo-binary and their ternary alloys in both phases and show a considerable deviation from Vegard＇s law. It is observed that the predicted lattice parameter and bulk modulus are in good agreement with the available experimental and theoretical data. We establish that the composition dependence of band gap is semi-metallic in B1 phase, while a direct band gap is observed in B3 phase. The calculated density of states is described by taking into account the contribution of Zn 3d, O 2p, and Se 4s, and the optical properties are studied in terms of dielectric functions, refractive index, reflectivity, and energy loss function for the B3 phase and are compared with the available experimental data.     

掺Ga对ZnO电子态密度和光学性质的影响

采用密度泛函理论下的第一性原理平面波赝势方法,研究了掺Ga对纤锌矿ZnO电子态密度和光学性质的影响.从晶体配位场理论分析了掺Ga前后ZnO的成键情况及态密度的变化.计算得到掺Ga后电子浓度为2.42×10²¹ cm^-3,ZnO的载流子浓度提高了10⁴倍.比较分析掺Ga前后ZnO的介电函数、复折射率、吸收光谱和反射光谱可得,ZnO光吸收边向高能端移动,光学带隙增大.在可见光区,ZnO光吸收系数与反射率减小,光透过率显著提高,使ZnO:Ga成为 关键词： 密度泛函理论 态密度 光学性质 ZnO:Ga     

三明治结构graphene-2Li-graphene的储氢性能

本文使用密度泛函理论中的广义梯度近似对扩展三明治结构graphene-2Li-graphene的几何结构、电子性质和储氢性能进行计算研究.计算得知:位于单层石墨烯中六元环面心位上方的单个Li原子与基底之间的结合能最大(1.19 eV),但小于固体Li的实验内聚能(1.63 eV),然而,在双层石墨烯之间的单个Li原子与基底的结合能增加到3.41 eV,远大于固体Li的实验内聚能,因此位于双层石墨烯之间的多个Li原子不会成簇,有利于进一步储氢.扩展三明治结构graphene-2Li-graphene中每个Li原子最多可以吸附3个H_2分子,储氢密度高达10.20 wt.%,超过美国能源部制定的5.5 wt.%的目标.该体系对1—3个H_2分子的平均吸附能分别为0.37,0.17和0.12 eV,介于物理吸附和化学吸附(0.1—0.8 eV)之间,因此该体系可以实现常温常压下对H_2的可逆吸附.通过对态密度分析可知,每个Li原子主要通过电场极化作用吸附多个H_2分子.动力学和巨配分函数计算表明graphene-2Li-graphene结构对H_2分子具有良好的可逆吸附性能.该研究可以为开发良好的储氢材料提供一个好的研究思路,为实验工作提供理论依据.     

First-principles study of electronic and optical properties in wurtzite Zn1-xCuxO

We perform a first-principles simulation to study the electronic and optical properties of wurtzite Zn1 xCuxO.The simulations are based upon the Perdew-Burke-Ernzerhof form of generalised gradient approximation within the density functional theory.Calculations are carried out in different concentrations.With increasing Cu concentration,the band gap of Zn1 xCuxO decreases due to the shift of valence band.The imaginary part of the dielectric function indicates that the optical transition between O 2p states in the highest valence band and Zn 4s states in the lowest conduction band shifts to the low energy range as the Cu concentration increases.Besides,it is shown that the insertion of Cu atom leads to redshift of the optical absorption edge.Meanwhile,the optical constants of pure ZnO and Zn0.75Cu0.25O,such as loss function,refractive index and reflectivity,are discussed.