反位缺陷对碳化硅纳米管电子结构和光学性质影响研究

采用基于密度泛函理论的第一性原理计算对含有反位缺陷（5,5）单壁碳化硅纳米管的电子结构和光学性质进行了研究.纳米管进行结构优化的结果显示,C_Si缺陷在纳米管表面形成了凹陷,Si_C缺陷形成了凸起;反位缺陷在纳米管的导带底附近形成了缺陷能级,使纳米管表现出n型导电的特点,由价带顶到缺陷能级的跃迁,在垂直和平行于纳米管管轴方向上形成了新的介电峰.     

CeO2的电子结构，光学和晶格动力学性质：第一性原理研究

基于考虑了Ce-4f电子间的库仑作用U和交换作用J的LDA+U方案,应用第一性原理计算系统研究了CeO₂的电子结构,光学和晶格动力学性质.电荷密度和电子局域函数的分布特征表明,CeO₂是属于共价键的绝缘体.介电常数、玻恩有效电荷张量和声子色散曲线的计算值和相应的实验结果符合得比较好.关键词：电子结构光学性质晶格动力学第一性原理计算     

C/SiC纳米管异质结电子结构的第一性原理研究

采用基于密度泛函理论的第一性原理计算,对扶手椅型(4,4)和(6,6)及锯齿型(8,0)和(10,0)C/SiC纳米管异质结的电子结构进行了研究.结果表明两类异质结结构都表现为半导体特性.扶手椅型纳米管异质结形成了Ⅰ型异质结,电子和空穴都限制在碳纳米管部分.锯齿型纳米管异质结中价带顶主要分布在碳纳米管部分及C/SiC界面处,而导带底均匀分布在整个纳米管异质结上.这两种异质结结构在未来纳米器件中具有潜在的应用价值.关键词：C/SiC纳米管异质结第一性原理电子结构     

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.     

不同浓度Er掺杂Si纳米晶粒电子结构和光学性质的第一性原理研究

利用基于密度泛函理论的第一性原理,对不同浓度Er掺杂Si纳米晶粒的结构稳定性、电子和光学性质进行了研究.结果表明: Si纳米晶粒中Er掺杂浓度越低,结构越稳定;Er掺杂后的Si纳米晶粒引入了杂质能级,导致禁带宽度变窄;掺杂后的Si纳米晶粒在低能区出现了一个较强的吸收峰,随着浓度的降低,吸收峰峰值逐渐减小,甚至消失. 这为Si基发光材料的设计提供了理论依据.关键词：Si纳米晶粒掺杂电子结构光学性质     

镍掺杂硅纳米线电子结构和光学性质的第一性原理研究

利用基于密度泛函理论的第一性原理计算,对镍掺杂硅纳米线的结构稳定性、电子与光学性质进行了研究.结果表明:Ni容易占据硅纳米线表面的替代位置.镍掺杂后的硅纳米线引入了杂质能级,杂质能级主要来源于Ni的3d电子的贡献.由于Ni的3d态和Si的3p态的耦合作用,使禁带宽度变窄.掺杂后的硅纳米线在低能区出现了一个较强的吸收峰,且吸收带出现宽化现象.关键词：硅纳米线掺杂电子结构光学性质     

The under-pressure behaviour of mechanical,electronic and optical properties of calcium titanate and its ground state thermoelectric response

Abstract

In this study, the elastic, electronic, optical and thermoelectric properties of CaTiO₃ perovskite oxide have been investigated using first-principles calculations. The generalised gradient approximation (GGA) has been employed for evaluating structural and elastic properties, while the modified Becke Johnson functional is used for studying the optical response of this compound. In addition to ground state physical properties, we also investigate the effects of pressure (0, 30, 60, 90 and 120 GPa) on the electronic structure of CaTiO₃. The application of pressure from 0 to 90 GPa shows that the indirect band gap (Γ-M) of CaTiO₃ increases with increasing pressure and at 120 GPa it spontaneously decreases transforming cubic CaTiO₃ to a direct (Γ-Γ) band gap material. The complex dielectric function and some optical parameters are also investigated under the application of pressures. All the calculated optical properties have been found to exhibit a shift to the higher energies with the increase of applied pressure suggesting potential optoelectronic device applications of CaTiO₃. The thermoelectric properties of CaTiO₃ have been computed at 0 GPa in terms of electrical conductivity, thermal conductivity and Seebeck coefficient.     

α和β-Si3N4的电子、光学及热力学性质的第一性原理计算

基于密度泛函理论的第一性原理方法,计算了α-Si₃N₄和β-Si₃N₄的晶体结构、电子结构、光学性质和声子谱,并对结果进行了理论分析.计算结果表明两种相都含有较强的共价键,均为绝缘体,且α-Si₃N₄的禁带宽度略大于β-Si₃N₄.计算获得的光学吸收系数表明α-Si₃N₄和β-Si₃N₄主要吸收紫外光,并二者的能量损失峰在24.4 eV附近.α-Si₃N₄和β-Si₃N₄的声子谱中均无虚频,表明二者的结构是稳定的.在0～1000 K范围内,α-Si₃N₄的热容约为β-Si₃N₄的两倍.本文的计算结果可以为Si₃N₄     

Sr掺杂对CaMnO_3基氧化物电子性质及热电输运性能的影响

采用密度泛函理论计算分析的方法研究了Ca位Sr掺杂的CaMnO_3基氧化物的电子性质和电性能;采用柠檬酸溶胶-凝胶法结合陶瓷烧结制备工艺制备了Ca位Sr掺杂的CaMnO_3基氧化物块体试样,分析研究了所得试样的热电传输性能.结果表明,Sr掺杂CaMnO_3氧化物仍然呈间接带隙型能带结构,带隙宽度由0.756 eV减小到0.711 eV.Sr掺杂CaMnO_3氧化物费米能级附近的载流子有效质量均得到调控,载流子浓度也有所增大.Sr比Ca具有更强的释放电子能力,其掺杂在CaMnO_3氧化物中表现为n型.Sr掺杂的CaMnO_3基氧化物材料电阻率大幅度降低,Seebeck系数绝对值较本征CaMnO_3基氧化物材料有一定程度的增大,Sr掺杂量为0.06和0.12的Ca_(1-x)Sr_xMnO_3(x=0.06,0.12)试样,其373 K的电阻率分别降低至本征CaMnO_3基氧化物材料的25%和21%,其373 K的Seebeck系数绝对值分别是本征CaMnO_3基氧化物材料的112.9%和111.1%,Sr掺杂有效提高了CaMnO_3基氧化物材料的热电性能.     

CoSi电子结构第一性原理研究

采用基于第一性原理的密度泛函理论全势线性扩展平面波法,首先对CoSi的晶胞参数进行优化计算,CoSi多粒子系统的最低能量为-134684297Ry,此时其晶胞处于最稳态,与最稳态对应的晶胞体积V0等于5899360a.u.3,晶胞参数为a=b=c=04438nm;然后计算了优化后的CoSi的电子结构及Si侧Al掺杂的CoSi075Al025的电子结构并分析了两者的电子结构特征,计算的CoSi电子能态密度与已有的计算结果整体形貌相同,但存在局部差异,Al掺杂后费米面发生了偏移;最后探讨了两者的电子结构对热电性能的影响,Al掺杂可提高CoSi的材料参数B,因此有望提高其热电性能.关键词：第一性原理电子结构热电性能     

First-principles study of lattice dynamics and thermodynamics ofosmium under pressure

We have performed the first-principles linear response calculations of the lattice dynamics, thermal equation of state and thermodynamical properties of hcp Os metal by using the plane-wave pseudopotential method. The thermodynamical properties are deduced from the calculated Helmholtz free energy by taking into account the electronic contribution and lattice vibrational contribution. The phonon frequencies at Gamma point are consistent with experimental values and the dispersion curves at various pressures have been determined. The calculated volume, bulk modulus and their pressure derivatives as a function of temperature are in excellent agreement with the experimental results. The calculated specific heat indicates that the electronic contribution is important not only at very low temperatures but also at high temperatures due to the electronic thermal excitation. The calculated Debye temperature at a very low temperature is in good agreement with experimental values and drops to a constant until 100~K.     

Transition metal encapsulated hydrogenated silicon nanotubes: Silicon-based half-metal

One-dimensional hydrogenated silicon nanotubes (H-SiNTs) with transition metal atom encapsulated were systematically studied by using density functional theory. The band structures and magnetic properties of the H-SiNTs can be tailored by doping transition metal (TM) (TM = Cr, Mn, Fe, Co) atoms within the tube. The hydrogenated silicon nanotubes are semiconductors with wide band gaps. TM doping turns H-SiNTs to be metals or semiconductors with a very small gap, and TM atoms at the center of the tubes keep large magnetic moments. Robust half-metallicity is observed in Mn-doped H-SiNTs and it is free from Peierls distortion. Thus, H-SiNTs with encapsulated magnetic elements may find important applications in spintronic devices.