Electronic structure of twinned ZnS nanowires

The electronic properties of twinned ZnS nanowires (NWs) with different diameters were investigated based on first-principles calculations. The energy band structures, projected density of states and the spatial distributions of the bottom of conduction band and the top of the valence band were presented. The results show that the twinned nanowires exhibit a semiconducting character and the band gap decreases with increasing nanowire diameter due to quantum confinement effects. The valence band maximum and conduction band minimum originate mainly from the S-p and Zn-s orbitals at the core of the nanowires, respectively, which was confirmed by their spatial charge density distribution. We also found that no heterostructure is formed in the twinned ZnS NWs since the valence band maximum and conduction band minimum states are distributed along the NW axis uniformly. We suggest that the hexagonal (2H) stacking inside the cubic (3C) stacking has no effect on the electronic properties of thin ZnS NWs.     

Te掺杂单层MoS2的电子结构与光电性质

采用基于密度泛函理论的第一性原理计算,研究了Te掺杂对单层MoS₂能带结构、电子态密度和光电性质的影响。结果表明,本征单层MoS₂属于直接带隙半导体材料,其禁带宽度为1.64 eV。本征单层MoS₂的价带顶主要由S-3p态电子和Mo-4d态电子构成,而其导带底则主要由Mo-4d态电子和S-3p态电子共同决定;Te掺杂单层MoS₂为间接带隙半导体材料,其禁带宽度为1.47 eV。同时通过Te掺杂,使单层MoS₂的静态介电常数增大,禁带宽度变窄,吸收光谱产生红移,研究结果为单层MoS₂在光电器件方面的应用提供了理论基础。     

LaPO4和ScPO4电子结构和光学性质的第一性原理研究

本文采用基于密度泛函理论的第一性原理平面波赝势方法,对LaPO₄和ScPO₄的能带结构、电子态密度及光学性质进行计算和分析.计算结果表明：LaPO₄的禁带宽度为5.646 eV,ScPO₄的禁带宽度为4.531 eV. LaPO₄晶体价带顶主要由P-3s、P-3p及O-2p态贡献,导带底主要是由La-5d态贡献;ScPO₄晶体价带顶主要由P-3s、P-3p及O-2p态贡献,导带顶主要是由Sc-3d态贡献.就光学性质而言,ScPO₄的静介电常数是2.03,比LaPO₄(1.92)的静介电常数大,体系极化能力较好.     

B、N单掺杂3C-SiC电子结构和光学性质的第一性原理研究

采用第一性原理的密度泛函理论赝势平面波方法,计算了未掺杂与B、N单掺杂3C-SiC的电子结构和光学性质.结果表明:掺杂改变了3C-SiC费米面附近的电子结构;B掺杂使得禁带宽度减小,价带顶上移,费米能级进入价带,形成p型半导体;N掺杂使得禁带宽度减小,导带底下移,费米能级进入导带,形成n型半导体.B、N掺杂均提高了3C-SiC在低能区的折射率、消光系数和吸收系数,增强了对红外光谱的吸收.     

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.     

Uniaxial strain-modulated electronic structures of CdX (X = S,Se, Te) from first-principles calculations:A comparison between bulk and nanowires

Using first-principles calculations based on density functional theory, we systematically study the structural deformation and electronic properties of wurtzite CdX(X = S, Se, Te) bulk and nanowires(NWs) under uniaxial [0001] strain. Due to the intrinsic shrinking strain induced by surface contraction, large NWs with {10ˉ10} facets have heavy hole(HH)-like valence band maximum(VBM) states, while NWs with {11ˉ20} facets have crystal hole(CH)-like VBM states. The external uniaxial strain induces an HH–CH band crossing at a critical strain for both bulk and NWs, resulting in nonlinear variations in band gap and hole effective mass at VBM. Unlike the bulk phase, the critical strain of NWs highly depends on the character of the VBM state in the unstrained case, which is closely related to the size and facet of NWs. The critical strain of bulk is at compressive range, while the critical strain of NWs with HH-like and CH-like VBM appears at compressive and tensile strain, respectively. Due to the HH–CH band crossing, the charge distribution of the VBM state in NWs can also be tuned by the external uniaxial strain. Despite the complication of the VBM state, the electron effective mass at conduction band minimum(CBM) of NWs shows a linear relation with the CBM–HH energy difference, the same as the bulk material.     

P掺杂硅纳米管电子结构与光学性质的研究

采用基于密度泛函理论的第一性原理计算,研究了P掺杂对单壁扶手型硅纳米管电子结构和光学性质的影响.结果表明:经过P掺杂,单壁扶手型硅纳米管的能带结构从间接带隙变为直接带隙,其价带顶主要由Si-3p态电子构成,导带底主要由Si-3p态电子和Si-3s态电子共同决定;同时通过P掺杂,使单壁扶手型硅纳米管的禁带宽度变窄,导电性增强,吸收光谱产生红移.研究结果为硅纳米管在光电器件方面的应用提供了理论基础.     

Mg掺杂CdSe电子结构和光学性质的第一性原理

采用基于密度泛函理论的第一性原理平面波超软赝势法,计算了纤锌矿结构Cd1-xMgxSe(x=0,0.125,0.250,0.375)的电子结构和光学性质。结果表明,不同系统的价带顶都主要由Se4p态决定,其位置基本不变;导带底由Se4 s态和Cd5 s共同决定,并且随着掺杂浓度的增加向高能区移动,结果使得带隙展宽,由此使得系统介电函数虚部的峰值和折射率实部的峰值随掺杂浓度的增大而蓝移,计算结果与实验符合。     

Cr和C共掺TiO_2的电子结构和光学性质的研究

利用第一性原理计算,研究了Cr与C共掺锐钛矿型TiO_2的能带的结构,态密度和光学性质.我们构建了两种不等价的Cr与C紧邻共掺体系:CrC_1-TiO_2和CrC_2-TiO_2.CrC_1-TiO_2体系在价带上方出现了主要由C-2p轨道和Cr-3d轨道耦合成的子带.同时,由于姜-泰勒变形效应,Cr-3d轨道的t_(2g)轨道进一步分裂的成Cr-3d_(yz)轨道在导带底形成附加带,有效带隙较纯TiO_2相比变窄了0.84eV.CrC_2-TiO_2体系带隙中有深带隙态存在,由于深间隙态的存在,价带顶到深带隙的能量宽度为0.84eV,电子从价带顶转移到导带底的所需要的能量将大大减小.最后,我们对纯TiO_2和Cr与C紧邻共掺TiO_2的光学特性进行了计算.结果显示Cr与C共掺TiO_2的光学吸收谱都有很好的可见光区域分布,大大提高了太阳光的利用率.     

Electronic structure and optical properties of Mg_xZn_(1-x)S bulk crystal using first-principles calculations

We perform the first-principles calculations within the framework of density functional theory to determine the elec- tronic structure and optical properties of MgxZnl-xS bulk crystal. The results indicate that the electronic structure and optical properties of MgxZnl_xS bulk crystal are sensitive to the Mg impurity composition. In particular, the MgxZnl-xS bulk crystal displays a direct band structure and the band gap increases from 2.05 eV to 2.91 eV with Mg dopant compo- sition value x increasing from 0 to 0.024. The S 3p electrons dominate the top of valence band, while the Zn 4s electrons and Zn 3p electrons occupy the bottom of conduction band in MgxZnl_xS bulk crystal. Moreover, the dielectric constant decreases and the optical absorption peak obviously has a blue shift. The calculated results provide important theoretical guidance for the applications of MgxZn1-xS bulk crystal in optical detectors.     

A first-principles study of the size-dependent electronic properties of SiC nanotubes

We investigate the structural and electronic properties of SiC nanotubes(NTs) with hexagonal cross sections by a first-principles calculation using plane-wave ultra-soft pseudo-potential technology based on the density-functional theory.Our results reveal that surface-layer C and Si atoms relax significantly upon decreasing the tube-wall thickness because of surface-size and quantum-size effects.We also find that all relaxed SiC NTs stay stably on the nanoscale because of an admixture of sp2 and sp3 hybridization between C and Si atoms and a strong covalent,and that the band gap tends to decrease with increasing tube-wall thickness.Our calculations further indicate that both C and Si atoms on the inner and outer surface of SiC NTs contribute to defect states at the top of the valence band and at the bottom of the conduction band.These results provide reference information for a thorough understanding of the properties of SiC nanostructures and also enable more precise monitoring and control of the growth of SiC nanostructures.     

应力效应对tP10-FeB_4的电子结构与光学性质的影响

由于具有高强度、超硬度、良好的热稳定性和半导体性质等特点,tP10-FeB_4可以在高温、高压的条件下使用,所以本文采用密度泛函理论,深入研究高压下tP10-FeB_4的电子结构和吸收系数、反射率、折射率等光学性质并得出了如下几点结论:随着压强的增大,电子的重叠增大,进而导致轨道杂化、能带宽度变宽,压缩带隙. tP10-FeB_4的价带顶部和导带底部主要由Fe的3d、B的2p和2s轨道构成. tP10-FeB_4在紫外区间有良好的吸收谱,是潜在的紫外吸收材料.而在可见光区吸收较小且对可见光的折射率比较大,因此可以考虑用于制作光导纤维.     

稀土元素(La,Y)掺杂GaN的第一性原理计算

采用基于密度泛函理论的第一性原理赝势平面波方法,对稀土元素La,Y单掺杂和La和Y共掺杂GaN的晶格常数、电子结构及光学性质进行了计算与分析.计算结果表明:掺杂改变了GaN的能带结构,未掺杂和Y掺杂形成导带底和价带顶位于G点的直接带隙半导体,而La掺杂和La和Y共掺杂形成导带底位于G点,价带顶位于Q点的间接带隙半导体.可以通过掺杂元素来调制GaN的禁带宽度和带隙类型,掺杂均提高GaN在低能区的静态介电常数、反射率、折射率,使光子的跃迁强度增大,说明稀土元素La,Y掺杂可有效调制GaN的光电性质.     

Mn,Fe,Co掺杂GaAs电子结构与光学性质的第一性原理研究

采用基于密度泛函理论的平面波超软赝势方法对本征GaAs以及3d过渡金属Mn、Fe、Co单掺杂GaAs晶体的电子结构及其光学性质进行理论计算以及对比研究.计算结果表明:能带结构中三种掺杂体系均引入新的能级,能带条数增多,导带底与价带底顶向深能级移动,带隙减小;费米能级附近出现了杂质能级,导致掺杂体系光子能量位于0时介电函数虚部便有所响应,掺杂体系相较于本征体系的静介电常数有所提升;Mn、Fe、Co三种掺杂体系相较于本征体系在红外以及远红外区域吸收系数得到了明显的提升,其中Fe掺杂GaAs的光催化特性最好.     

过渡金属(Ni)掺杂ZnV2O4的第一性原理计算

采用基于密度泛函理论下的MS软件模拟了过渡金属Ni掺杂ZnV₂O₄前后的能带结构、态密度以及光学性质.结果表明：ZnV₂O₄具有间接的光学跃迁且能带间隙为0.355 eV,Ni掺杂后能带间隙增加为0.785 eV,且带隙类型不变,引入的Ni-3d轨道电子对ZnV₂O₄的价带和导带组成提供了较大贡献.光学性质结果表明ZnV₂O₄为一种低介电材料,在可见光区的吸收系数和折射率较低,主要表现为紫外吸收.掺杂Ni后,在可见光区的吸收特性和光电导率均增大,有效改善了ZnV₂O₄在可见光区的光电性能.     

Density functional theory analysis of electronic structure and optical properties of La-doped Cd_2SnO_4 transparent conducting oxide

The electronic structural, effective masses of carriers, and optical properties of pure and La-doped Cd_2SnO_4 are calculated by using the first-principles method based on the density functional theory. Using the GGA+U method, we show that Cd_2SnO_4 is a direct band-gap semiconductor with a band gap of 2.216 eV, the band gap decreases to 2.02 e V and the Fermi energy level moves to the conduction band after La doping. The density of states of Cd_2SnO_4 shows that the bottom of the conduction band is composed of Cd 5 s, Sn 5 s, and Sn 5 p orbits, the top of the valence band is composed of Cd 4d and O 2p, and the La 5 d orbital is hybridized with the O 2 p orbital, which plays a key role at the conduction band bottom after La doping. The effective masses at the conduction band bottom of pure and La-doped Cd_2SnO_4 are 0.18 m0 and 0.092 m_0, respectively, which indicates that the electrical conductivity of Cd_2SnO_4 after La doping is improved. The calculated optical properties show that the optical transmittance of La-doped Cd_2SnO_4 is 92%, the optical absorption edge is slightly blue shifted, and the optical band gap is increased to 3.263 eV. All the results indicate that the conductivity and optical transmittance of Cd_2SnO_4 can be improved by doping La.     

N-S共掺杂金红石相TiO2电子结构与光学性质的第一性原理研究

采用基于第一性原理的平面波超软赝势方法研究N和S单掺杂以及N和S共掺杂金红石相TiO2的能带结构,态密度和光学性质.结果表明:N掺杂导致禁带宽度减小为1.43 eV,并且在价带上方形成了一条杂质能带;S掺杂导致费米能级上移靠近导带,直接带隙减小为0.32 eV;N和S共掺杂导致能带结构中出现了两条杂质能带,靠近导带的一条杂质能级距离导带底约0.35 eV,靠近价带的一条杂质能级距离价带顶约0.85 eV,杂质能级主要由N原子的2p轨道和S原子的3p轨道组成.N和S掺杂后不但使TiO2的吸收带产生红移,而且在可见光区具有较大的吸收系数,光催化活性增强.     

三嵌段共聚物的电子结构及态密度特征

采用紧束缚近似计算方法,针对小带隙的聚乙炔(polyacetylene,(PA))和大带隙的聚对苯撑(poly(p-phenylene),(PPP)组成的三嵌段共聚物(triblock copolymer)-(PA)x-(PPP)n-(PA)y-和-(PPP)x-(PA)n-(PPP)y-性质进行了研究,发现它们具有典型的量子阱特征.对均聚物PPP和PA以及三嵌段共聚物的态密度(density of states, (DOS))进行了计算分析,发现共聚物的态密度与均聚物的态密度有着显著的区别,共聚物的带隙的大小介于大带隙的PPP和小带隙的PA之间,在共聚物中与PPP的导带和价带的子带隙以及共聚物的导带底和价带顶中,所存在的能态密度只能由PA来提供,而在共聚物的价带底和导带顶的能态密度则取决于PPP的态密度.     

Sc2O3电子结构和光学性质的第一性原理研究

本文基于第一性原理平面波赝势(PWP)和广义梯度近似(GGA)方法,研究了Sc2O3的电子结构、态密度和光学性质. 计算结果表明：Sc2O3是一种直接带隙半导体,其能带宽度为3.79eV,价带顶部主要由O的2p和Sc的3p3d杂化而成,导带主要由Sc的3d和O的2p构成. 同时,文中也分析了Sc2O3的介电函数、折射率、光电导率和吸收谱等光学性质. 计算得到静态介电常数 ,折射率n0=1.25,在紫外区有较大的吸收系数.     

聚乙炔极化子的新电子束缚态

本文用自洽迭代的方法研究了SSH模型中极化子的电子能谱。结果发现,除了禁带中两个在TLM模型中存在的深能级电子束缚态外,还存在四个浅能级的电子束缚态。它们形成分立的能级,并分别位于导带的顶部和底部以及价带的顶部和底部。价带顶和导带底的两个束缚态只在一定的耦合参量λ范围内出现。 关键词：