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。     

3C-SiC材料p型掺杂的第一性原理研究

采用基于第一性原理的密度泛函理论平面波超软赝势法,研究了SiC材料p型掺杂的晶体结构和电子结构性质,得到了优化后体系的结构参数,掺杂形成能,能带结构和电子态密度,计算得到掺杂B,Al,Ga在不同浓度下的禁带宽度.结果表明:随着掺杂B原子浓度的增大,禁带宽度随之减小;而随着掺杂Al,Ga原子浓度的增大,禁带宽度随之增大;在相同浓度下,掺杂Ga的禁带宽度大于掺杂Al,掺Al禁带宽度大于掺B. 关键词： SiC 电子结构 掺杂 第一性原理软件     

碳掺杂闭口硼氮纳米管场发射第一性原理研究

运用第一性原理研究了闭口硼氮纳米管（BNNT）顶层掺碳体系（C@BNNT）的电子场发射性能.结果表明：随外电场增强,C@BNNT电子结构变化显著,态密度（DOS）向低能方向移动;碳原子的局域态密度（LDOS）在费米能级附近明显增大;赝能隙、最高占据分子轨道（HOMO）/最低未占据分子轨道（LUMO）能隙减小;体系电荷移向帽端.DOS,HOMO/LUMO及Mulliken电荷分析一致表明,与BNNT相比,C@BNNT电子场发射性能显著改善,且C@BN_moreNT性能更优. 关键词： 碳掺杂 硼氮纳米管 电子场发射 第一性原理     

不同浓度C掺杂SnO_2的第一性原理计算

采用基于密度泛函理论的第一性原理对不同浓度C掺杂SnO_2体系的晶体结构、能带结构、态密度以及光学性质进行了计算.结果表明:掺杂C原子后,晶胞体积和晶格常数都略微增大,且随着掺杂浓度的增大而增大,能带的禁带宽度则随着浓度的增大而减小.在光学性质中,掺杂C原子后体系的光吸收边都向低能方向移动,随着掺杂浓度的增大,体系红移的幅度也增大.     

Mn掺杂GaN稀磁半导体的电磁特性研究

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不同浓度Mn掺杂GaN（Ga1-xMnxN, x=0.0625和0.1250）的晶格常数、能带结构和态密度,分析比较了掺杂前后GaN的电子结构和磁性。结果表明：Mn掺入后体系仍为直接带隙半导体,带隙宽度随Mn含量的增加逐步增大。Mn掺杂GaN均使得N 2p与Mn 3d轨道杂化,产生自旋极化杂质带,自旋向上的能带占据费米面,掺杂后的Ga1-xMnxN表现为半金属铁磁性,适合自旋注入;随着Mn掺杂浓度的增加,体系的半金属性有所增强。     

稀土元素Gd掺杂BiFeO3的第一性原理研究

采用基于密度泛函理论的局域自旋密度近似加U法（LSDA+U:Hubbard参数）计算了多铁材料BiFeO3铁电相以及稀土元素Gd掺杂BiFeO3材料的能带结构、态密度（DOS）、原子轨道占据数和净电荷分布等,对稀土元素Gd掺杂BiFeO3可能引起的电子结构、介电常数和铁磁性的改变进行了第一性原理研究。计算结果表明：Gd掺杂对材料钙钛矿结构影响不大,BiFeO3铁电性主要来源于Fe原子3d轨道和O原子2p轨道杂化;掺杂Gd后材料中的Fe原子和O原子的共价性减弱,Bi原子和O原子的离子性增强,禁带宽度变窄,绝缘性减弱,铁磁性明显增强;计算得到的光学性质表明材料的静态介电常数有所增加。     

扶手椅型硅纳米管的电学性质研究

本文采用密度泛函理论的第一性原理方法,对手性指数m=n=K（K为3～15的整数）的扶手型硅纳米管的能带结构和态密度进行了研究。计算结果表明,扶手型（3,3）硅纳米管为间接带隙结构,其余均为直接带隙结构;随着手性指数的增加,硅纳米管的直径增大,硅纳米管的禁带宽度逐渐减小,且导带逐渐下移,总态密度图峰值强度增大;扶手型（3,3）硅纳米管的禁带宽度最大;扶手型（13,13）硅纳米管的禁带宽度最小,说明其导电性优于其他手性指数的扶手椅型硅纳米管;同时,扶手型（4,4）硅纳米管的导带和价带出现重叠,说明扶手型（4,4）硅纳米管为金属性纳米管;态密度图表明扶手型（9,9）硅纳米管的价带顶主要由Si-3p电子态构成,导带底由Si-3p态电子和Si-3s态电子共同构成。     

稀土元素Gd掺杂BiFeO3的第一性原理研究

采用基于密度泛函理论的局域自旋密度近似加U法（LSDA+U:Hubbard参数）计算了多铁材料BiFeO3铁电相以及稀土元素Gd掺杂BiFeO3材料的能带结构、态密度（DOS）、原子轨道占据数和净电荷分布等,对稀土元素Gd掺杂BiFeO3可能引起的电子结构、介电常数和铁磁性的改变进行了第一性原理研究。计算结果表明：Gd掺杂对材料钙钛矿结构影响不大,BiFeO3铁电性主要来源于Fe原子3d轨道和O原子2p轨道杂化;掺杂Gd后材料中的Fe原子和O原子的共价性减弱,Bi原子和O原子的离子性增强,禁带宽度变窄,绝缘性减弱,铁磁性明显增强;计算得到的光学性质表明材料的静态介电常数有所增加。     

稀土元素La掺杂β-FeSi2的几何结构和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赝势平面波方法,对稀土元素La掺杂β-FeSi2的几何结构、能带结构、态密度进行了理论计算.几何结构的计算表明:La掺杂后使β-FeSi2的晶格常数a、b、c都变大了,使得晶胞体积也相应增大;La掺杂β-FeSi2的置换位置为FeⅡ位.电子结构的计算表明:能带结构为直接带隙,禁带宽度变窄仅为0.013eV;费米面进入价带,能带数目增多,态密度峰值减小,费米面附近载流子浓度显著增大.这些结果为β-FeSi2光电材料掺杂改性的实验和理论研究提供理论依据.     

Einstein relation in chemically doped organic semiconductors

Based on the assumption of Gaussian energy distributions of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), analytical expressions of generalized Einstein relation in chemically doped organic semiconductor are developed, by approximation of Coulomb traps with a rectangle potential well. Numerical calculations show that traditional Einstein relations do not hold for chemically doped organic semiconductors. Similar to physical doping, the dependence of diffusion coefficient to mobility D/μ ratio on the carrier concentration has a maximum. An essential difference between chemical doping and physical doping is that, the D/μ ratio in chemically doped organic semiconductors depends not only on carrier concentration and doping concentration, but also on the applied electric field. PACS 71.20.Rv; 72.90.+y; 73.50.-h     

Self-consistent theory for the built-in voltage in metal–organic semiconductor–metal structures

A self-consistent theory for calculation of built-in voltage (U_bi) of metal–organic semiconductor–metal (MOSM) structures is developed based on Gaussian energy distribution of highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO). It is shown that the built-in voltage depends not only on the work function difference of the two electrodes, but also on the mean energy level of HOMO and LUMO, as well as the Gaussian width of the energy distribution. The theory predicts that the spreading of HOMO and LUMO levels will results in an increase of U_bi, and that U_bi decreases with increasing temperature.     

Evolution of the unoccupied states in alkali metal-doped organic semiconductor

The evolution of the electronic structure, especially the unoccupied states, induced by alkali metal doping has been investigated with photoemission and inverse photoemission spectroscopy for organic semiconductors, such as copper-phthalocyanine (CuPc) and tris(8-hydroxyquinoline) aluminum (Alq). The n-type doping leads to a downward shift for the lowest unoccupied molecular orbital (LUMO) of the organic semiconductors, until the edge of the LUMO reaches the Fermi level. After that, the LUMO intensity decreases monotonically, while a gap state grows in the valence spectra, which gives direct evidence for the origin of the doping-induced gap state in organic molecules. The modification of the LUMO intensity, as well as that of the gap state, suggests the formation of multiply charged anions in heavily doped film.     

Generalization of Einstein relation for doped organic semiconductors

Under the assumption of Gaussian energy distributions of the lowest unoccupied molecular orbital (LUMO) and the highest occupied molecular orbital (HOMO), analytical expressions of generalized Einstein relation for electron and hole transport in doped organic semiconductor thin films are developed. Numerical calculations show that, although traditional Einstein relation still holds for low carrier concentrations, that is, the diffusion-coefficient-to-mobility ratio in units of k_BT/q, with k_B the Boltzmann’s constant, T the temperature and q the elementary charge, equals 1. But when the electron (hole) concentration is high, the diffusion-coefficient-to-mobility ratio for electrons (holes) changes strongly with the electron (hole) concentration, the doping level, the mean energy of LUMOs (HOMOs) of the dopant E_Ld (E_Hd) and the host E_L (E_H), as well as their variances. Dopants with E_Ld<E_L (E_Hd>E_H) affect the diffusion-coefficient-to-mobility ratio mainly in the range of low and middle carrier concentrations, while those with E_Ld>E_L (E_Hd<E_H) have significant effect only in the range of high carrier concentrations. It was found that there can be a maximum in the dependence of the diffusion-coefficient-to-mobility ratio on the quasi-Fermi energy or carrier concentration exist, for appropriate values of the doping level, the mean energy and variance of LUMO or HOMO states of the dopant. PACS 71.20.Rv; 72.90.+y; 73.50.-h     

Matlab编程的Hückel分子轨道法计算研究掺杂纳米碳管的化学反应性

使用Matlab自编简单Hückel分子轨道法（SHMO）计算程序,分析空位、Stone-Wales缺陷位、N和B原子掺杂的CNT（5,5）碳纳米管,计算π电子密度和前线分子轨道（HOMO和LUMO）为研究掺杂相对碳纳米管的化学反应性提供依据.具有不同电特性的掺杂相打破了碳纳米管的π电子、HOMO和LUMO的均衡分布.掺杂相和/或邻近的碳原子为HOMO或LUMO贡献了较其它原子更大的轨道系数,在不同的化学反应中表现出良好的亲核性或亲电性.此外,HOMO-LUMO能量差很好地反映了掺杂纳米碳管的导电性.计算结果与已报道的实验和理论结果吻合良好.     

外电场下GaN的特性研究

以6-311G(3df,3pd)为基组,采用B3PW91方法优化得到GaN基态分子的几何结构,并探究了电场对GaN分子基态能量、电荷布居数、键长、偶极矩、振动频率、红外光谱强度、HOMO、LUMO能级影响.研究表明:无电场时,谐振频率值为576.2218 cm~(-1),与实验值484.9 cm~(-1)很接近.有电场时,键长、偶极矩、能隙Eg、电荷布居数、红外谱强度、HOMO和LUMO能级随电场的增大而减小;谐振频率和分子总能量随电场的增加而增加.谐振频率和红外谱强度对电场有着明显的依赖关系,这对材料的光学特性研究有提供理论参考.     

Structural and electronic properties of endohedral doped SWCNTs: A DFT study

The structural and electronic properties of semiconductors (Si and Ge) and metal (Au and Tl) atoms doped armchair (n, n) and zigzag (n, 0); n=4–6, single wall carbon nanotubes (SWCNTs) have been studied using an ab-initio method. We have considered a linear chain of dopant atoms inside CNTs of different diameters but of same length. We have studied variation of B.E./atom, ionization potential, electron affinity and HOMO–LUMO gap of doped armchair and zigzag CNTs with diameter and dopant type. For armchair undoped CNTs, the B.E./atom increases with the increase in diameter of the tubes. For Si, Ge and Tl doped CNTs, B.E./atom is maximum for (6, 6) CNT whereas for Au doped CNTs, it is maximum for (5, 5) CNTs. For pure CNTs, IP decreases slightly with increasing diameter whereas EA increases with diameter. The study of HOMO–LUMO gap shows that on doping metallic character of the armchair CNTs increases whereas for zigzag CNTs semiconducting character increases. In case of zigzag tubes only Si doped (5, 0), (6, 0) and Ge doped (6, 0) CNTs are stable. The IP and EA for doped zigzag CNTs remain almost independent of tube diameter and dopant type whereas for doped armchair CNTs, maximum IP and EA are observed for (5, 5) tube for all dopants.     

Molecules relevant for organic photovoltaics: a range-separated density functional study

Accurate determination of both fundamental and optical gap is necessary for designing molecules relevant for organic photovoltaics. Here, we study how range-separated density functionals reproduce frontier orbital energies, HOMO (highest occupied molecular orbital)–LUMO (lowest unoccupied molecular orbital) gaps, and optical gaps for molecules relevant for organic photovoltaics. In this study, we consider 12 different range-separated density functional for computing HOMO energy, HOMO–LUMO gap, and optical gap which are compared with available experimental and reported GW values. We found that the reproduction of desired photovoltaic properties primarily depend on range separation parameter. Moreover, the tested functionals are comparable with OT-BNL functional.     

Electrical Conductivity in Polyazomethines: A Novel Mechanism Derived from All Valence MO Calculation and IR Study of Polymer–Dopant Interaction

A simple mechanism is proposed to explain the variation of electrical conductivity in polyazomethines. The results of semiempirical, all valence, molecular orbital calculations obtained from the PM3 method have been employed to arrive at the mechanism. The difference of energy (ΔE) between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) alone could not explain the variation in electrical conductivity; however, ΔE together with the LUMO electron density at the atoms that lie on the continuous chain could account for the electrical conductivity in these polymers. The LUMO electron density on these centers may be visualized as the carrier movement. In certain polymers there are intrinsic holes in HOMO. The movement of these intrinsic holes also adds to the electrical conduction. The polyazomethines are prepared by the condensation of diamines with azo bis-aldehydes. A few of these polymers were doped with silver nanoparticles. Many of the doped polymers showed substantial enhancement in conductivity. Strong polymer–dopant interaction, identified by IR spectroscopy, is proposed to be responsible for the increase in conductivity.     

Density functional investigation on the structures and properties of Li atom doped Au20 cluster

Structures and properties of an Au₂₀ cluster doped with two Li atoms, Au₁₈Li₂, have been investigated using relativistic density functional theory within the framework of the zeroth-order regular approximation. Various initial structures have been generated and employed for geometry optimization followed by vibration analysis to check the stability of the final optimized structures. We have calculated various properties like binding energy, ionization potential, electron affinity and the HOMO–LUMO gap of these structures. It has been found that two dopant Li atoms favour occupying two different surface positions of the pyramidal Au₂₀ cluster. The binding energy of the surface-doped Au₁₈Li₂ cluster is 1.017?eV higher than that of the pure Au₂₀ cluster and the HOMO–LUMO gap (1.742?eV) is as high as a pure Au₂₀ cluster (1.786?eV). Interestingly, we observe that the HOMO–LUMO gap as well as the binding energy can be increased beyond those of the Au₁₈Li₂ cluster with the help of further Li atom doping. In fact, a doped tetrahedral Au₁₆Li₄ cluster, where all the dopants are at the surface sites, possesses a very high HOMO–LUMO gap of 2.117?eV. Geometric and energetic parameters indicate that the Au₁₆Li₄ cluster might be considered as a possible ‘superatom’ in the design of novel cluster-assembled materials.