F覆盖度对石墨烯体系电子结构和光学性能的影响

为了研究不同F覆盖度下石墨烯吸附体系的电子结构和光学性能,采用第一性原理对本征石墨烯和石墨烯吸附体系进行了几何优化,计算并分析了各体系的吸附能、能带结构、电子态密度、光吸收系数与反射率.结果表明,F原子稳定吸附在石墨烯的顶位,当F覆盖度为6.2%时,体系吸附能最大.F原子的吸附打开了石墨烯的能隙,使其由半金属型转变为半导体型.当F覆盖度为3.1%时,体系能隙值最大.与本征石墨烯相比,石墨烯吸附体系在费米能级处的电子态密度值增大,当F覆盖度为9.4%时,可以获得最大态密度值.石墨烯吸附体系的光吸收系数和反射率峰值相比本征石墨烯均明显减小,且F覆盖度越大,峰值减小程度越显著.在一定波长范围内吸附体系的吸收系数和反射率均出现蓝移现象.     

稀土元素Gd掺杂GaN的电子结构和磁学性质研究

采用基于密度泛函理论(DFT)结合投影缀加平面波(PAW)的方法,通过VASP软件包计算研究了稀土元素Gd掺杂GaN的晶格参数、形成能、电子态密度、能带结构和磁学性质.计算过程中将稀土元素Gd的4f电子计入价电子,采用LSDA+U方法处理4f电子的强关联效应.计算结果表明:Gd原子之间的耦合是反铁磁性的,当有足够的空穴载流子存在时能够稳定铁磁相;Ga空位虽然能够提供空穴稳定铁磁相,但是由于在p型GaN中Ga空位的形成能较高而难以形成;而间隙N缺陷和间隙O缺陷的形成能较低,能够稳定GaN∶Gd体系的铁磁相并且能够分别引入1μB和2μB的磁矩,因此认为间隙N和O可能是巨大磁矩的来源.     

封口型单壁碳纳米管电子结构的密度泛函研究

采用密度泛函(DFT)的B3LYP基组和非平衡格林函数方法对封口型单壁碳纳米管及在碳纳米管外接Au电极的纳米器件的量子结构、密利根电荷分布、电子传输和态密度等特性进行了理论研究.结果发现HOMO (Highest Occupied Molecular Orbital)和LUMO(Lowest Unoccupied Molecular Orbital)间的能隙Eg=0.973 8 eV,呈现半导体特征;态密度与电子输运谱具有很好的对应关系;电子输运主要集中在能量E＜O.O eV的区域.     

氟化碳化硅片的电子和磁性结构研究

通过密度泛函理论研究了氟化碳化硅片的电子结构和磁性特点,碳化硅中的硅原子被氟化,结果发现氟化的碳化硅片是带隙约为1.04eV的反铁磁半导体。通过简单的氟化,实现了材料由无磁性向反铁磁的转变,调节了材料的带隙,这预示着在未来的纳米功能材料中可能的应用。     

硼氮掺杂对锯齿型硅烯纳米带器件中 自旋输运的调控

采用密度泛函理论和非平衡格林函数方法,研究了硼和氮原子单独掺杂对锯齿型硅烯纳米带器件中自旋输运行为的调控作用。研究发现硼和氮原子都是掺杂在锯齿型硅烯纳米带的边缘最稳定。硼和氮原子的掺杂区域对器件的自旋输运性质起着关键作用:当掺杂在器件的散射区时,可发现微小的自旋劈裂现象;但是当掺杂在电极区时,会出现较明显的自旋劈裂现象,相应的自旋过滤效率可高达100%。     

立方相WO_3电子结构及其(001)活性表面吸附性能

采用基于密度泛函理论的第一性原理方法探讨了WO3的电子结构和表面性能,进行了能带结构、态密度和有效电子质量的模拟计算,对WO3吸附12种原子后的吸附体系进行了理论分析。结果表明,WO3价带顶主要是由O的2p态电子构成,导带底主要是由W的5d态电子构成。当价带顶上的O-2p电子吸收能量后可跃迁至导带底的W的5d轨道上,同时在O-2p上产生空穴。其电子迁移率为1.35,表明其电子-空穴的分离率较高,光催化活性较强。探讨了WO3的(001)洁净表面对12种非金属原子的吸附情况,WO3吸附F原子后表面能最小。     

聚酰亚胺几何结构和电子结构的分子模拟

依据密度泛函(DFT)理论,利用PW 91方法,对聚酰亚胺二、三和四聚体进行模拟,研究其几何结构和电子结构.模拟结果表明,聚酰亚胺二、三和四聚体中间片断的键长、键角基本一致,采用低聚物中间片断结构,可以表征整个高分子聚合物结构,随着聚合度N的增加,总能量降低,能隙减小.     

ZnO晶格常数优化和电子结构的第一性原理研究

采用基于密度泛函理论(DFT)框架下局域密度近似平面波超软赝势法,计算了纤锌矿ZnO的晶格常数、弹性模量、能带结构和态密度。理论预测ZnO是一种直接禁带半导体材料,导带底和价带顶都位于布里渊区中心G点处。计算结果与其他文献结果吻合较好,为ZnO光电材料的设计与应用提供了理论依据。     

Electronic structure of SiC (310) twin boundary doped with B,N, Al and Ti

Doping of boron, nitrogen, aluminum and titanium in the SiC (310) twin boundary was investigated, and the first-principle calculation was used to analyze the underlying mechanism of excellent creep resistance and strength of Sylramic and Tyranno SA SiC fibers. The electronic structures were also analyzed and compared. The results of Mulliken overlap populations, electron density differences and density of states reveal that doping of B or N atom reinforces SiC GBs bonding, however, doping of Al or Ti atom weakens SiC GBs bonding. The reinforced SiC GBs will largely prevent atoms from sliding near GBs. The experimental results would be one of the reasons which lead to the reinforcement of either creep resistance or the strength of SiC fibers. Funded by the National Natural Science Foundation of China (50642039) and the Doctorate Foundation of Northwestern Polytechnical University (CX2004012)     

镍团簇的结构与电子性质

在相对论有效原子实势(RECP)近似下,用Gaussian98程序和密度泛函中的B3LYP/LANL2DZ方法,对纯Nin(n=2-6)团簇的各种几何构型进行优化计算,得到它们的基态结构、垂直电离势和电子亲和能.结果表明,Ni2分子的基电子态为3Σ+u,Ni3的基态结构是等腰三角形,电子态为3B2.由于Jahn-Teller效应,Ni4的基态结构为具有C2v对称性的蝶形结构,电子态为7A2.Ni5和Ni6的基态结构也具有C2v对称性,分别为梯形和三角形结构,对应的基电子态分别为7A1和3B2.最后计算了团簇的能级分布和最高占据轨道(HOMO)与最低空轨道(LUMO)之间的能级间隙(HLG),分析了团簇的化学活性.     

Electronic structure and flotation behavior of monoclinic and hexagonal pyrrhotite

Electronic structures of monoclinic and hexagonal pyrrhotite were studied using density functional theory method,together with their flotation behavior. The main contribution of monoclinic pyrrhotite is mainly from Fe 3d, while that of hexagonal pyrrhotite is from Fe 3d, Fe 3p and S 3s. The hexagonal pyrrhotite is more reactive than monoclinic pyrrhotite because of large density of states near the Fermi level. The hexagonal pyrrhotite shows antiferromagnetism. S—Fe bonds mainly exist in monoclinic pyrrhotite as the covalent bonds, while hexagonal pyrrhotite has no covalency. The main contributions of higest occupied molecular orbital(HOMO) and lowest unoccupied molecular obital(LUMO) for monoclinic pyrrhotite come from S and Fe. The main contribution of HOMO for hexagonal pyrrhotite comes from Fe, while that of LUMO comes from S. The coefficient of Fe atom is much larger than that of S atom of HOMO for hexagonal pyrrhotite, which contributes to the adsorption of Ca OH+ on the surface of hexagonal pyrrhotite when there is lime. As a result, lime has the inhibitory effect on the floatation of hexagonal pyrrhotite and the coefficient of Fe is very close to that of S for monoclinic pyrrhotite. Therefore, the existence of S prevents the adsorption of Ca OH+on the surface of monoclinic pyrrhotite, which leads to less inhibitory effect on the flotation of monoclinic pyrrhotite.     

Electronic transport properties of cross graphene nano-junction

Graphene nanoribbons have special electrical properties, The electron transport properties can be regulated by controlling their geometry or doping. The metallic properties and semiconductor properties of different chiral graphene nanoribbons are used to build the cross graphene nano-junction in this paper. The method of density functional theory and non-equilibrium Green's function are used to research electronic transport properties of the graphene nano-junction with different heights and widths and locations of doping. It is shown that the graphene nano-junction shows metallic properties with increase in height and width of the arm. But the transmission spectral line has a clear oscillation. Since the doped nitrogen atom intensifies electron scattering, the electronic transport properties decrease. And the electron transport properties when the two arms are doped worsens more compared to the case of trunk doping.     

Thermoelectric Properties and Electronic Structure of Ca_3Co_2O_6

1　IntroductionIthasbeengenerallyacceptedthatthethermoelectricefficiencyofoxidesislowerthanthatoftheconventionalthermoelectricmaterialbecauseoftheirhighioniccharacter,whichgenerallycausesastronglocalizationofelectronsandhenceleadstoaverylowcarriermobility…     

四方晶相HfO_2在(100)和(001)方向上光学特性的理论计算

文章采用基于密度泛函理论(DFT)框架下广义梯度近似平面波超软赝势法,计算了四方晶相Hf0_2的电子结构.经带隙校正后,计算了四方晶相Hf0_2在(100)和(001)方向上的光学线性响应函数随光子能量的变化关系,包括复介电函数、复折射率、吸收光谱以及反射光谱.计算结果表明四方晶相Hf0_2在(100)和(001)方向上具有明显的光学各向异性,并且具有从紫外到红外的透明区域.文中计算结果与其它文献报道的计算结果及实验值都吻合较好,由此说明采用密度泛函理论的广义梯度近似来计算HfO_2材料的光学特性是可信的.     

温度对V2O3系材料电子结构的影响

采用自洽场离散变分Xα（SCC-DV-Xα）方法对（V0.9950Cr0.0025Al0.0025）2O3体系分别处于25℃及200℃时的电荷分布、态密度、能级结构等进行了研究。结果表明,温度对电子结构的影响导致材料的电导率发生显著变化,变化趋势与实验结果相一致,对钒系PTC材料的进一步研制具有理论指导意义。