Cd掺杂纤锌矿ZnO电子结构的第一性原理研究

采用密度泛函理论结合投影缀加波方法,对掺杂Cd导致ZnO禁带宽度下降的机理进行了研究. 通过对掺杂前后电子能带结构,态密度以及分态密度的计算和比较,发现Cd_xZn_1-xO价带顶端(VBM)始终由O-2p占据;而导带顶端(CBM)则由Cd-5s与Zn-4s杂化轨道控制. 随着掺杂浓度的增加,决定带隙宽度的CBM的位置下降,同时VBM的位置上升,从而导致了带隙的变窄,出现了红移现象. 此外,Cd掺杂会使晶胞发生膨胀,这种张应变也是导致Cd 关键词： 密度泛函理论 电子结构 Cd掺杂ZnO     

Cd掺杂纤锌矿ZnO电子结构的第一性原理研究

采用密度泛函理论结合投影缀加波方法，对掺杂Cd导致ZnO禁带宽度下降的机理进行了研究. 通过对掺杂前后电子能带结构，态密度以及分态密度的计算和比较，发现Cd_xZn_1-xO价带顶端(VBM)始终由O-2p占据；而导带顶端(CBM)则由Cd-5s与Zn-4s杂化轨道控制. 随着掺杂浓度的增加，决定带隙宽度的CBM的位置下降，同时VBM的位置上升，从而导致了带隙的变窄，出现了红移现象. 此外，Cd掺杂会使晶胞发生膨胀，这种张应变也是导致Cd     

Mg掺杂ZnO所致的禁带宽度增大现象研究

采用第一性原理的超软赝势方法，研究了纤锌矿ZnO及不同量Mg掺杂ZnO合金的电子结构.理论计算表明，Mg的掺杂导致ZnO晶体的禁带宽度增大.研究发现，Zn 4s态决定导带底的位置，Mg的掺入导致Zn 4s态向高能端的偏移是导致禁带宽度增大的根本原因. 关键词： 密度泛函理论 赝势 Mg掺杂ZnO     

Se掺杂ZnO的晶体结构和电子性质的第一性原理计算

本文采用基于第一性原理的密度泛函理论（DFT）平面波超软赝势方法,研究了纤锌矿ZnO及不同浓度Se掺杂ZnO合金的晶体结构和电子性质。在对Se掺杂结构优化的基础上对其进行了数值模拟计算,结果表明：ZnO1-xSex晶格常数随着Se浓度的增大而近似呈线性增加;禁带宽度随着浓度的增大先减小后增大;价带顶的位置由Se-4p态电子决定,且基本不随浓度变化而变化,导带底的位置主要由Zn-4s态电子,且随Se掺杂浓度的增加先向低能段移动然后向高能段移动,这也是带隙先变小后变大的根本原因。     

Se掺杂ZnO的晶体结构和电子性质的第一性原理计算

本文采用基于第一性原理的密度泛函理论（DFT）平面波超软赝势方法,研究了纤锌矿ZnO及不同浓度Se掺杂ZnO合金的晶体结构和电子性质。在对Se掺杂结构优化的基础上对其进行了数值模拟计算,结果表明：ZnO1-xSex晶格常数随着Se浓度的增大而近似呈线性增加;禁带宽度随着浓度的增大先减小后增大;价带顶的位置由Se-4p态电子决定,且基本不随浓度变化而变化,导带底的位置主要由Zn-4s态电子,且随Se掺杂浓度的增加先向低能段移动然后向高能段移动,这也是带隙先变小后变大的根本原因。     

ZnO高掺杂Ga的浓度对导电性能和红移效应影响的第一性原理研究

采用基于密度泛函理论框架下的第一性原理平面波超软赝势方法,在相同环境条件下建立了浓度不同的由Ga原子取代Zn原子的Zn_1-xGa_xO模型.对低温高掺杂Ga原子的Zn_1-xGa_xO半导体的能带结构、态密度和吸收光谱进行了计算.结果表明:Ga原子浓度越大,进入导带的相对电子数越多,但是电子迁移率反而减小.通过对掺杂和未掺杂ZnO的电导率以及最小间隙带宽度分别进行了比较 关键词： ZnO高掺杂Ga 电导率 红移 第一性原理     

纤锌矿CdxZn1-xO电子结构的第一性原理研究

采用第一性原理的平面波超软赝势方法,计算了纤锌矿ZnO及不同量Cd掺杂ZnO的电子结构.计算结果表明,Cd的掺杂导致ZnO晶体的禁带宽度变窄.主要原因在于Cd的掺入导致Zn4s轨道中能级越来越低的电子参与作用,使得决定导带底的反键Zn 4s态能级逐渐降低,同时由pd反键轨道控制的价带顶能级逐渐升高. 关键词： 密度泛函理论 超软赝势方法 Cd掺杂ZnO     

Be和Ca掺杂纤锌矿ZnO的晶格常数与能带特性研究

利用密度泛函理论平面波的赝势方法,对Be、Ca掺杂纤锌矿ZnO的BexZn1-xO,CayZn1-xO三元合金和BexZn1-xO,CayZn1-xO四元合金的晶格常数、能带特性和形成能进行计算,结果表明：BexZn1--xO晶格常数随Be掺杂量的增大线性减小,但CayZn1-yO晶格常数随ca掺杂量的增大而增大．BexZn1-xO和CayZn1-yO能带的价带顶都由O2p态电子占据,导带底由Zn4s态电子占据,其能隙随Be或Ca掺杂量的增大而变宽．由Be和Ca共掺ZnO得到的Be0．125Ca0．125Zn0．75O四元合金,其晶格常数与ZnO相匹配,能隙比ZnO大,稳定性优于Be0．25Ca0．125Zn0.625O和Be0．5Zn0．50合金,Be0．125Ca0．125Zn0.75O／ZnO异质结构适合制作高质量ZnO基器件．     

Ga掺杂ZnO的电子结构与电性能的研究

采用密度泛函理论广义梯度近似第一性原理计算的方法研究了n型Ga掺杂的纤锌矿结构氧化物ZnO的晶格结构、能带结构和态密度,在此基础上分析了其电性能.计算结果表明,掺杂ZnO氧化物晶格a,b轴增大,c轴略有减小;Ga掺杂ZnO氧化物两能带之间具有0.6eV的直接带隙,需要载流子(电子)跃迁的能隙宽度较未掺杂的ZnO氧化物减小;掺杂体系费米能级附近的态密度大大提高,其能带主要由Gas态、Zns态和Os态电子构成,且他们之间存在着强相互作用,其中Gas态电子对导带贡献最大.电输运性能分析结果表明,Ga掺杂ZnO氧化物导电机构由Znp-Op电子在价带与导带的跃迁转变为Gas-Znd-Os电子在价带与导带的跃迁,这也表明Gas态电子在导电过程中的重要作用;掺杂体系费米能级附近的载流子有效质量较未掺杂体系增大,且价带中的载流子有效质量较大,导带中的载流子有效质量较小.     

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.     

Electronic properties of orthorhombic LiGaS<Subscript>2</Subscript> and LiGaSe<Subscript>2</Subscript>

We report theoretical calculations of the band structure and density of states for orthorhombic LiGaS₂ (LGS) and LiGaSe₂ (LGSe). These calculations are based on the full potential linear augmented plane wave (FP-LAPW) method within a framework of density functional theory. Our calculations show that these crystals have similar band structures. The valence band maximum (VBM) and the conduction band minimum (CBM) are located at Γ, resulting in a direct energy band gap. The VBM is dominated by S/Se-p and Li-p states, while the CBM is dominated by Ga-s, S/Se-p and small contributions of Li-p and Ga-p. From the partial density of states we find that Li-p hybridizes with Li-s below the Fermi energy (E _F), while Li-s/p hybridizes with Ga-p below and above E _F. Also, we note that S/Se-p hybridizes with Ga-s below and above E _F.     

Exploring the electronic structure of Pb2+ ions containing material Pb16(OH)16(NO3)16

A theoretical band structure calculation for lead nitrate hydroxide Pb₁₆(OH)₁₆(NO₃)₁₆ single crystal was performed based on the experimental crystallographic data obtained by Chang et al. Calculations exhibit that the conduction band minimum (CBM) is situated at Γ the center of the Brillouin zone (BZ) while the valence band maximum (VBM) is located between Γ and Y points of the BZ, resulting in an indirect energy band gap of about 3.70 eV in close agreement to the measured one (3.78 eV). The angular momentum resolved projected density of states reveals the existence of the strong hybridization between the orbitals and the VBM is originated from Pb-6s/6p and O-2p orbitals while the CBM from N-2p and Pb-6p orbitals. The calculated valence electronic charge density distribution explore the bond characters and the dominancy of the covalent bonding between Pb–O of PbO_n ployhedra and N–O of [NO₃]⁻ triangle. The calculated bond lengths and angles show good agreement with the experimental data.     

First-principles energy band calculation for undoped and N-doped InTaO4 with layered wolframite-type structure

The electronic structures of undoped and N-doped InTaO₄ with optimized structures are calculated within the framework of the density functional theory. Calculated lattice constants are in excellent agreement with experimental values, within a difference of 2%. The valence band maximum (VBM) is located near the middle point on the ZD line and the conduction band minimum (CBM) near the middle point on the DX line. This means that InTaO₄ is an indirect-gap material and a minimum theoretical gap between VBM and CBM is ca. 3.7 eV. The valence band in the range from −6.0 to 0 eV mainly consists of O 2p orbitals, where In 4d5s5p and Ta 5d orbitals are slightly hybridized with O 2p orbitals. On the other hand, the conduction band below 5.5 eV is mainly composed of the Ta 5d orbitals and the contributions of In and O orbitals are small. The band gap of N-doped InTaO₄ decreases by 0.3 eV than that of undoped InTaO₄, because new gap states originating from N 2p orbitals appear near the top of the valence band. This result indicates that doping of N atoms into metal oxides is a useful method to develop photocatalysts sensitive to visible light.     

Electronic structures and effective masses of photogenerated carriers of CaZrTi2O7 photocatalyst: First-principles calculations

The band structures, density of states and effective masses of photogenerated carriers for CaZrTi₂O₇ photocatalyst were performed using first principles method with the virtual crystal approximation. The results indicated that CaZrTi₂O₇ has an indirect band gap of about 3.25 eV. The upper valence bands of CaZrTi₂O₇ are formed by O 2p states mixed with Ti 3d states, Zr 4d, 4p and 5s states, while the conduction bands are dominated by Ti 3d states, Zr 4d states and O 2p states. The calculated valence bands maximum (VBM) potential is located at 2.60 V (vs. normal hydrogen electrode (NHE)), while the conduction bands minimum (CBM) potential at ?0.65 V. Therefore, CaZrTi2O7 has the ability to split water to hydrogen and oxygen under UV light irradiation. The calculated minimum effective mass of electron in CBM is about 1.35 m₀, and the minimum effective mass of hole in VBM is about 1.23 m₀. The lighter effective masses facilitate the migration of photogenerated carriers and improve photocatalytic performance.     

Calculations of electronic structure and density of states in?the?wurtzite structure of Zn1? x Mg x O alloys using sp3 semi-empirical tight-binding model

Calculating the electronic structure and the density of states in the wurtzite structure of Zn_1−x Mg _x O (ZMO) alloys using sp³ semi-empirical tight-binding model, we observed increases of both band gap and electron effective mass that agree with the experimental results as increasing Mg composition up to x=0.3. From the calculated total density of states, the increasing electron effective mass is a result of less orbital overlap of cation sites due to extra density of modes coming from Mg3s and Mg3p orbitals as introducing more Mg composition. Additionally, reducing electronegative characteristic of oxygen was caused by that the O2p was less localized around the oxygen atom.     

Lattice strain and p-d repulsion affecting electronic structure of wurtzite Zn1-xCdxO alloys

In the paper, density of states, band structure and electron density difference of Zn1-xCdxO are calculated by first principles, here x varies from 0 to 0.75 at intervals of 0.125, and the band gap obtained from band structure changes from 0.968 eV to 0.043 eV. The lattice strain and p-d repulsion theory are used to investigate variation of the band gap, the results obtained show that the variation is mainly due to the lattice tensile strain. The p-d repulsion in Zn1-xCdxO cannot be neglected. In addition, electron density difference can be used to verify the results.     

纤锌矿BeO掺Cd的电子结构与能带特性研究

采用基于密度泛函理论平面波赝势方法, 对纤锌矿BeO掺Cd的Be_1-xCd_xO合金进行电子结构与能带特性研究. 结果表明: Be_1-xCd_xO的价带顶始终由O 2p电子态决定, 而导带底由Be 2s和Cd 5s的电子态决定.随着Be_1-xCd_xO合金的Cd掺杂量增加, Cd 4d与O 2p的排斥效应逐渐加强, 同时Be_1-xCd_xO的带隙逐渐变小, 出现"直接-间接-直接"的带隙转变. 为了使理论值与实验值相一致, 对Be_1-xCd_xO带隙进行修正, 并分析了纤锌矿BeO-ZnO-CdO三元合金的带隙和弯曲系数与晶格常数的关系.     

Electronic structural properties and formation energy of Sn1−xPbxO2 solid solutions electrode

First-principles calculations based on density functional theory within the generalized gradient approximation have been performed for the Sn_1−xPb_xO₂ solid solution. The doped formation energies and electronic structures are also analyzed. Results show that the Sn_0.9375Pb_0.0625O₂ solid solution has the highest stability because of its minimum formation energy value of 0.04589 eV at a doping ratio of 0.0625. The SnO₂ lattice constants expand in a distorted rutile structure after Pb doping. The band structure and density of states calculations indicate that the band gap of SnO₂ narrowed due to the presence of the Pb impurity energy levels in the forbidden band, namely, Pb 6s energy band overlaps with the conductivity band in the F–Q direction. In addition, the number of electrons filled at the bottom of the conduction band increases from 0.13 to 3.96 after doping, resulting in the strengthening of the conductivity of the solid solution after doping of plumbum. The results provide a theoretical basis for the development and application of the Sn_1−xPb_xO₂ solid solution electrode.