Prediction of the Frontier Electronic States in a Finite Single-wall Carbon Nanotube

A theoretical model is summarized into the shorter vector principle. It is used to predict the topological structure of wave function and the oscillation rule of energy gap in various types of finite carbon nanotubes (CNTs). The theoretical model indicates that the characteristics of the electronic states only depend on the nanotube size and its symmetry along the shorter vector direction. In this direction, the wave functions of the original 3m (or 3m/2) periodicity are also suitable for armchair, chiral and zigzag finite CNTs with the C2 (Cs), C1 and Cn point groups, respectively. Energy gaps present the oscillation with 3m (or 3m/2) or odd-even n. The first principle calculations for some prototype systems are performed. The results are consistent with the theoretical model.     

A First-principles Study on the Gas Sensitivity of Metal-loaded Graphene with an Atomic Vacancy to O_2

In this work, adsorption energies, geometrical and electronic structures for adsorption systems of O_2 at metal-loaded graphene(M-Gra) and metal-loaded defective graphene(M-D-Gra)(M = Ni, Pd, Pt and Al) surfaces are studied using a GGA-PW91 method. Calculated results show that loaded M make the interaction between O_2 and the graphene surface change from physical to chemical adsorptions, band gaps of M-Gra systems after the O_2 adsorption change, and the Ni-loaded Gra has the highest sensitivity to O_2. For O_2-M-D-Gra systems, interactions between O_2 and the M-D-Gra surfaces are chemical, similar to the O_2-M-Gra systems, and loaded Pt and Al have the strongest effect on the sensitivity of D-Gra to O_2. The M loads at the perfect Gra and D-Gra surfaces make the interactions between O_2 and the surfaces have obvious charge transfer. This work would provide a valuable guidance on the gas sensitivity study of graphene to O_2.     

CaO或BaO与Sm2O3共掺杂CeO2体系电子结构和氧离子迁移的DFT+U研究

使用GGA+U方法研究了Ca O或Ba O与Sm2O3共掺杂Ce O2体系几何和电子结构及氧离子迁移。计算结果表明,Ba和Sm均靠近氧空位时Ba Sm Ce30O63体系最稳定;Sm靠近,Ca远离氧空位时Ca Sm Ce30O63体系最稳定。Ba Sm Ce30O63和Ca Sm Ce30O63体系中均不存在Ce4+变价。对Ca Sm Ce30O63体系氧离子迁移的研究发现,当氧离子迁移到空位时,迁移能大小顺序为Em(3→V)Em(1→V)Em(4→V)Em(2→V),这一规律源于氧离子与低价掺杂离子产生负电势之间的排斥作用;对Ba Sm Ce30O63体系氧离子迁移的研究发现,当空位迁移到周围氧离子时,迁移能大小顺序为Em(V→3)Em(V→5)Em(V→1),这一规律源于氧空位产生的正电势与低价掺杂离子产生的负电势之间的吸引作用。此外,Ca Sm Ce30O63体系最小迁移能小于Sm Ce31O63体系,证实了Ce O2-Sm2O3-Ca O体系离子电导率大于Ce O2-Sm2O3体系的实验结果。     

Effects of Doping and Oxygen Vacancy Concentrations on Oxygen Ion Migration in Sm_xCe_(1-x)O_(2-δ): a DFT + U Study

Influence of doping and oxygen vacancy concentrations on oxygen ion or oxygen vacancy(V) migration energies of Sm_xCe_(1-x)O_(2-δ)(x = 0.0625, 0.125, 0.25 and δ = 0.0625, 0.125) systems using a GGA+U method are studied. Calculated results show that advantage migration types change from V?O~(2-) to O~(2-) ?V as x and δ increase. For V?O~(2-) migrations of the Sm_(0.0625)Ce_(0.9375)O_(1.9375) and Sm_(0.125)Ce_(0.875)O_(1.9375) systems, electrostatic attractions between Sm~(3+) and V, defect associations between Ce~(3+) and V, and steric hindrances of Sm~(3+) affect the migration energies. For O~(2-) ?V migrations of the Sm+(0.125)Ce_(0.875)O_(1.875) and Sm_(0.25)Ce_(0.75)O_(1.875) systems, migration energies of O~(~(2-) ) are affected by electrostatic repulsions between Sm~(3+) and O~(2-) and defect associations between Ce~(3+) and V. Increases of the oxygen vacancy and Sm~(3+) doping concentrations benefit the oxygen ion and vacancy migrations, respectively.     

Li在石墨烯、BC7及C7N表面吸附与迁移的第一性原理研究

基于密度泛函理论的第一性原理方法,本文系统研究了Li在本征石墨烯及BC7、C7N表面的吸附和迁移行为。与本征石墨烯相比,硼含量为12.5at%时提高了Li的吸附能,而氮含量为12.5at%时减弱了Li的吸附能,这归因于掺杂物种具有不同的电子结构。通过NEB方法计算了Li在本征石墨烯、BC7、C7N表面的迁移。结果表明,相比于本征石墨烯,硼含量为12.5at%的石墨烯减弱了Li的扩散,而氮含量为12.5at%的石墨烯促进了Li的扩散,有助于提高石墨烯负极材料的充放电性能。     

CaO或BaO与Sm2O3共掺杂CeO2体系电子结构和氧离子迁移的DFT+U研究

使用GGA+U方法研究了CaO或BaO与Sm₂O₃共掺杂CeO₂体系几何和电子结构及氧离子迁移。计算结果表明,Ba和Sm均靠近氧空位时BaSmCe₃₀O₆₃体系最稳定;Sm靠近,Ca远离氧空位时CaSmCe₃₀O₆₃体系最稳定。BaSmCe₃₀O₆₃和CaSmCe₃₀O₆₃体系中均不存在Ce⁴⁺变价。对CaSmCe₃₀O₆₃体系氧离子迁移的研究发现,当氧离子迁移到空位时,迁移能大小顺序为E_m(3→V)< E_m(1→V)< E_m(4→V)< E_m(2→V),这一规律源于氧离子与低价掺杂离子产生负电势之间的排斥作用;对BaSmCe₃₀O₆₃体系氧离子迁移的研究发现,当空位迁移到周围氧离子时,迁移能大小顺序为E_m(V→3)< E_m(V→5)< E_m(V→1),这一规律源于氧空位产生的正电势与低价掺杂离子产生的负电势之间的吸引作用。此外,CaSmCe₃₀O₆₃体系最小迁移能小于SmCe₃₁O₆₃体系,证实了CeO₂-Sm₂O₃-CaO体系离子电导率大于CeO₂-Sm₂O₃体系的实验结果。     

有限长锯齿型碳纳米管的电子结构与管径效应

在B3LYP／6—31G／／PM3水平上对一系列有限长锯齿型碳纳米管(n，0)(n=6-11)的构型和电子结构进行了研究．结果表明，最高占据轨道(HOMO)与最低空轨道(LUMO)间的能隙(Eg)随着管径的增大出现随奇偶n值的振荡变化，随着管长的增加呈单调减小的趋势；前线轨道波函数的成键结构随管径的变化而变化，但并不随管长的变化而改变，HOMO的成键性质与几何结构之间存在对应关系．     

Al掺杂的锂离子电池层状正极材料Li(Li0.17Ni0.17Al0.04Fe0.13Mn0.49)O2结构稳定性及氧离子氧化的理论研究

锂离子电池(LIB)正极材料比容量及结构稳定性的提高是提升电池整体性能的重要因素. 本工作选取层状无钴正极材料Li(Li_0.17Ni_0.17Al_0.04Fe_0.13Mn_0.49)O₂ (LNAFMO)为研究对象, 使用GGA (generalized gradient approximation)+U (Hubbard U value)方法研究了体系在充电时几何和电子结构变化、氧释放焓、脱锂形成能和脱锂电压. 研究结果表明, 充电时LNAFMO体系首先Ni氧化, 然后Fe氧化, 最后O氧化. 与未掺杂Al的Li(Li_0.17Ni_0.17Fe_0.17Mn_0.49)O₂ (LNFMO)体系不同的是, 除具有线性Li-O-Li和Fe-O-Li构型的氧离子更容易给出电子外, 具有线性Al-O-Li构型的氧离子也参与电荷补偿, 并且氧离子具有很强的活性, 这将避免参与氧化的氧离子过分集中, 有利于结构的稳定; Al的掺杂能进一步抑制氧的释放, 这将提升体系的结构稳定性和电池循环性能. 该研究为设计一种低经济成本、循环性良好、高能量密度的锂离子电池正极材料奠定了坚实的理论依据.     

椅型碳纳米管吸附氢原子电子结构的密度泛函研究

采用密度泛函方法对氢原子在(5,5)椅型碳纳米管上的吸附进行了研究, 分别考察了氢原子覆盖度为5%和10%时的构型和吸附能. 研究结果表明, H原子吸附在管外壁要比管内壁能量上更为有利, 同时第二个H原子倾向于吸附在前一个H原子的吸附位置邻近的碳原子上. 由能带计算结果得知, 吸附一个H原子时, 椅型碳纳米管将由导体转变为半导体; 当第二个H原子处在偶数位时, 纳米管仍保持较好的导电性能, 而吸附在奇数位时将使管的传输能力减弱. 本文进一步通过分析纳米管(共轭体系的分布情况对管传输性质的变化进行解释.     

金属掺杂的CeO2体系电子结构和氧离子迁移能的DFT+U研究

使用DFT和DFT+U方法研究了Ca,Ba,Sm与Zr在CeO₂体系中的掺杂能及其掺杂对缺陷形成能和氧离子迁移能的影响规律. 计算结果表明,对未含有氧离子空位的掺杂体系,掺杂能随着掺杂离子半径的增大而增大;对含有氧离子空位的掺杂体系,掺杂能受到掺杂离子半径和价态的影响;对各种掺杂体系电子结构的研究发现,在还原CeO₂,Zr和Sm掺杂的CeO₂体系中,由于氧空位捕获电子使Fermi能级升高;在碱土金属掺杂的CeO₂体系中,由于Ca²⁺和Ba²⁺取代高价态Ce⁴⁺而产生的负电荷恰恰与氧离子空位产生的正电荷中和,因此Fermi能级几乎没有移动;还原CeO₂和Zr掺杂的CeO₂体系均含有Ce³⁺,其新态位于Ce4f和O2p之间,这将导致CeO₂体系具有离子和电子导电特性;Ca,Ba和Sm的掺杂均抑制了CeO₂体系中Ce⁴⁺的变价. 使用NEB方法对氧离子迁移能进行了研究,且结果表明,氧离子到空位的迁移路径几乎沿一条直线进行;当掺杂Ca,Ba,Sm与Zr时,氧离子迁移能均小于纯CeO₂体系的;在这些掺杂体系中,Ba掺杂的体系氧离子迁移能最小,掺杂能较大,这可能导致在实验中常通过加入第三类掺杂物来引入Ba.