表面氢化双层硅烯的结构和电子性质

采用密度泛函理论(DFT)广义梯度近似GGA和HSB06方法研究了氢化双层硅烯(silicene)的结构和电子性质, 结果表明: 氢化后的双层硅烯可能存在三种稳定的构型, AA椅型、AB椅型和AA船型, 其中AA椅型和AB椅型结构最为稳定, 氢化后这三种稳定构型材料的性质由零带隙的半金属(semimetal)转变为禁带宽度分别为1.208, 1.437和1.111 eV 的间接带隙的半导体, 采用混合泛函HSB06计算修正得到的带隙分别为1.595, 1.785 和1.592 eV. 进一步分析了在双轴应变下氢化双层硅烯的带隙随应变的关系, 得到应变可以连续的调节材料的带隙宽度, 这些性质有可能应用于未来的纳米电子器件.     

二维BC2 N薄片的结构稳定性和电子性质

采用基于密度泛函理论的第一性原理方法,对二维BC₂N薄片的结构稳定性和电子性质进行了系统的研究.计算了BC₂N化合物16种可能的二维单层结构.对它们的能带结构分析发现,对称性最高的构型与石墨烯一样是一种半金属,而其他二维结构则为有不同带隙的半导体,其中最稳定的构型是带隙值为1.63 eV的直接带隙半导体.对最稳定构型的差分电荷密度分析和Bader分析发现:在最稳定的构型中,C–C键、C–N键、C–B键和B–N键主要以共价键的形式呈现,也具有比较明显的离子性.在应力作用下最稳定构型的单层BC₂N的带隙宽度会发生变化,压缩时带隙变宽,而拉伸时带隙变窄,但仍然为直接带隙半导体. 关键词： 2N')" href="#">BC₂N 单层原子薄片 电子结构 从头计算     

三氧化钨表面氢吸附机理的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,在广义梯度近似下,研究了立方WO_3,WO_3(001)表面结构及其氢吸附机理.计算结果表明立方晶体WO_3理论带隙宽度为0.587 eV.WO_3(001)表面有WO终止(001)表面和O终止(001)表面两种结构,表面结构优化后W—O键长和W—O—W键角改变,从而实现表面弛豫;WO终止(001)表面和O终止(001)表面分别呈现n型半导体特征和p型半导体特征.分别计算了H原子吸附在WO终止(001)表面和O终止(001)表面的H—O_(2c)—H,H—O_(2c)…H—O_(2c),H—O_(1c)—H和H—O_(1c)…H—O_(1c)四种吸附构型,其中H—O_(1c)—H吸附构型的吸附能最小,H—O键最短,H失去电子数最多,分别为-3.684 eV,0.0968 nm和0.55e,此吸附构型最稳定.分析其吸附前后的态密度,带隙从吸附前的0.624 eV增加到1.004 eV,价带宽度基本不变.H的1s轨道电子与O的2p,2s轨道电子相互作用,在-8和-20 eV附近各形成了一个较强的孤立电子峰,两个H原子分别与一个O_(1c)原子形成化学键,最终吸附反应生成了一个H_2O分子,同时产生了一个表面氧空位.     

MgS晶体结构性质的密度泛函研究

采用基于密度泛函理论(DFT)基础上的第一性原理赝势平面波方法对MgS晶体四种构型(B1，B2，B3，B4)的体相性质进行了系统研究.计算结果表明，B1构型的晶体是间接带隙型半导体，而B2，B3和B4构型的晶体则是直接带隙型材料，其中B2构型的带隙宽度最窄，其值为0.42eV.在压力不超过200.3GPa时，B1构型的MgS 晶胞是最稳定的，当压力大于该值时，会发生B1构型到B2构型的转化. 关键词： MgS 第一性原理赝势平面波方法 电子结构 转化压力     

锑烯吸附金属Li原子的密度泛函研究

锑烯(antimonene)是继石墨烯和磷烯之后出现的新型二维材料,在锂离子电池等领域受到关注.本文基于第一性原理的密度泛函理论,计算研究了锑烯对Li原子的吸附特性,包括Li原子的最稳定吸附构型、吸附密度以及吸附Li原子的扩散路径.结果表明:Li原子最稳定的吸附位置位于谷位,即底层Sb原子之上、顶层三个Sb原子中心位置,吸附能为1.69 eV,吸附距离为2.81?;能带计算发现,锑烯为带隙宽度1.08 eV的间接带隙半导体,吸附Li原子后费米能级上升进入导带,呈现出金属性;原子分波态密度分析发现, Sb原子的p电子态和Li原子的p和s电子态形成明显的共振交叠,表现出杂化成键的特征;随着吸附Li原子数量增加,锑烯晶格结构和电子结构发生较大变化.通过微动弹性带方法计算发现, Li原子在锑烯表面的扩散势垒为0.07 eV,较小的势垒高度有利于快速充放电过程.     

高压对氮化硼纳米管的几何结构、电子结构和光学性质的影响

运用密度泛函理论平面波赝势方法(PWP)和广义梯度近似(GGA),计算研究了纳米管BN(5,5)在不同压力条件下的几何结构、电子结构和光学性质. 在高压条件下管口形状发生了较大的变化. 与闪锌矿结构BN比较分析发现两种结构间存在一些性质上的差异：首先,在外压力作用下,BN(5,5)纳米管的带隙随压力增大而减小,变化率为-0.01795eV/GPa,而闪锌矿结构BN随压力增大而增大;其次光吸收谱在压力条件下,没有和闪锌矿结构BN一样发生“蓝移”,相反在红外方向有所拓展;但纳米管BN(5,5)电子的转移方向和 关键词： 氮化硼纳米管 密度泛函理论(DFT) 电子结构     

W_(20)O_(58)(010)表面氢吸附机理的第一性原理研究

采用基于密度泛函理论的第一性原理平面波超软赝势方法,在广义梯度近似下,研究了W_(20)O_(58)晶胞、W_(20)O_(58)(010)表面结构及其氢吸附机理.计算结果表明:W_(20)O_(58)晶体理论带隙宽度为0.8 eV,为间接带隙,具有金属性.W_(20)O_(58)晶体中W—O共振较强,以共价键居多.W_(20)O_(58)(010)表面有WO终止(010)表面和O终止(010)表面,表面结构优化后使得W—O键长和W—O—W键角改变,从而实现表面弛豫.分别计算了H_2分子吸附在WO终止(001)表面和O终止(001)表面的WO-L-O_(1c),WO-V-O_(1c),WO-L-O_(2c),WO-V-O_(2c),O-L-O_(1c)和O-V-O_(1c)六种吸附构型,其中WO-L-O_(1c),WO-V-O_(1c)和WO-L-O_(2c)这三种吸附构型不稳定;而WO-V-O_(2c),O-L-O_(1c)和O-V-O_(1c)这三种吸附构型都很稳定,H_2分子都解离成两个H原子,吸附能均为负值,分别为-1.164,-1.021和-3.11 eV.WO-V-O_(2c)吸附构型的两个H原子分别吸附在O和W原子上;O-L-O_(1c)吸附构型的两个H原子,一个与O原子成键,另一个远离了表面.其中O-V-O_(1c)吸附构型最稳定,两个H原子失去电子,为O原子提供电子.分析其吸附前后的态密度,H的1s轨道电子与O的2p,2s轨道电子相互作用,均形成了一些较强的成键电子峰,两个H原子分别与O_(1c)形成化学键,最终吸附反应生成了一个H_2O分子,同时产生了一个表面氧空位.     

BaZrO3和CaZrO3能带和光学性质的第一性原理研究

采用基于密度泛函理论基础上的CASTEP软件包,计算了BaZrO3和CaZrO3的能带以及光学性质.计算得到BaZrO3直接带隙和间接带隙分别为3.49 eV和3.23eV,CaZrO3直接带隙和间接带隙分别为3.73 eV和3.38 eV.对这两种材料的介电函数、吸收系数、反射系数、折射系数、湮灭系数和能量损失系数等光学系数进行了计算,并基于电子能带对光学性质进行了解释.得出,光学特性的异同是由于其内部微观结构上的异同所引起的.     

FLAPW方法研究δ-钚(001)面的性质

采用 FLAPW(全势线性缀加平面波)方法,在广义梯度近似(GGA)、反铁磁(AFM)下研究了δ-钚(001)面的性质.计算得到的表面能系数和功函数分别为0.08 eV/(A)2和3.15 eV,接近其近邻元素α-铀的实验值(0.094 eV/(A)2和3.4～3.9 eV).与体相原子相比,表层原子由于近邻原子数目的减少,5f-5f和5f-6d轨道波函数重叠、杂化几率降低,5f电子定域化特性增强,局部磁矩增大.表层原子向内收缩2.70%,然而,由于表面弛豫能很小,δ-钚(001)面相当稳定.     

弯曲BN纳米片的电子性质及其调制

BN纳米片是具有一定宽度、无限长度的一维蜂窝构型单层带状氮化硼材料,弯曲的BN纳米片因为P z轨道旋转,将表现出一定的独特的电子性质.通过第一性原理计算,利用MS(Material Studio)中的DMOL3(local density functional calculations on molecules)软件计算了Zigzag和Armchair型BN纳米片弯曲以后的能带结构.BN纳米带的带隙会随着弯曲角度的变化而改变,以Armchair型BN纳米带的变化较为明显;在弯曲的基础上再加入外电场,却是Zigzag型BN纳米带的带隙变化更显著.当电场加大到一定的值,纳米带就会从半导体变为金属,并且这一临界电场值的大小和纳米带的弯曲程度有关.电场对带隙的调制还和纳米带的尺寸有关系,电场对大尺度的纳米带的调控性更好,从半导体转变为金属所需要的电场值要更小.     

Orbital electronic heat capacity of hydrogenated monolayer and bilayer graphene

The tight-binding Harrison model and Green's function approach have been utilized in order to investigate the contribution of hybridized orbitals in the electronic density of states(DOS) and electronic heat capacity(EHC) for four hydrogenated structures, including monolayer chair-like, table-like, bilayer AA- and finally AB-stacked graphene. After hydrogenation, monolayer graphene and bilayer graphene are behave as semiconducting systems owning a wide direct band gap and this means that all orbitals have several states around the Fermi level. The energy gap in DOS and Schottky anomaly in EHC curves of these structures are compared together illustrating the maximum and minimum band gaps are appear for monolayer chair-like and bilayer AA-stacked graphane, respectively. In spite of these, our findings show that the maximum and minimum values of Schottky anomaly appear for hydrogenated bilayer AA-stacked and monolayer table-like configurations, respectively.     

Structural features and electronic properties of Group-IIIB pnictides nanosheets and nanoribbons

Two-dimensional (2D) materials exhibit unique electronic properties compared with their bulks. A systematical study of new type 2D tetragonal materials of MPn (M = Sc and Y; Pn = P, As and Sb) nanosheets and the corresponding nanoribbons are proposed by density functional theory calculations. Several thermodynamically stable 2D tetragonal structures were firstly determined, and such novel tetragonal structures bilayer MPn(100) exhibit extraordinary Weyl semimetal electronic structures, while monolayer MPn(110) are semiconductors. Moreover, bilayer MPn(100) nanoribbons with zigzag edges show metallic behavior, whereas those with linear edges show semiconducting properties. The band gaps for bilayer MPn(100) nanoribbons with linear edges can be significantly tuned by their widths. The zero-gap semiconducting behaviors of 2D tetragonal MPn nanosheets and the tunable band gaps of 1D MPn nanoribbons provide these MPn nanosheets and nanoribbons with promising applications in nanoscale electronic devices.     

Structural stabilities and electronic properties of fully hydrogenated SiC sheet

The intriguing structural and electronic properties of fully hydrogenated SiC honeycomb sheet are studied by means of ab initio calculations. Based on structure optimization and phonon dispersion analysis, we find that both chair-like and boat-like configurations are dynamically stable, and the chair-like conformer is energetically more favored with an energy gain of 0.03 eV per C atom relative to the boat-like one. The chair-like and boat-like conformers are revealed to be nonmagnetic semiconductors with direct band gaps of 3.84 and 4.29 eV, respectively, both larger than 2.55 eV of pristine SiC sheet. The charge density distributions show that the bondings are characterized with covalency for both chair-like and boat-like conformers.     

γ石墨炔衍生物结构稳定性和电子结构的第一性原理研究

通过基于密度泛函理论的第一原理计算,系统研究了γ石墨炔衍生物的结构稳定性、原子构型和电子性质.γ石墨炔衍生物的结构是由碳六元环以及连接六元环间的碳链组成,碳链上的碳原子数为N=1—6.研究结果表明,碳链上碳原子数的奇偶性对γ石墨炔衍生物的结构稳定和相应的原子构型、电子结构性质具有很大的影响.其奇偶性规律为:当六元环间的碳原子数为奇数时,体系中的碳链均为双键排布,系统呈现金属性;当六元环间的碳原子数为偶数时,系统中的碳链形式为单、三键交替排列,体系为直接带隙的半导体.直接带隙的存在能够促进光电能的高效转换,预示着石墨炔在光电子器件中的应用优势.N=2,4,6的带隙分布在0.94—0.84 eV之间,带隙的大小与碳链上三键的数量和长度有关.研究表明,将碳原子链引入到石墨烯碳六元环之间,通过控制引入的碳原子个数可以调控其金属和半导体电子特性,为设计和制备基于碳原子的可调控s-p杂化的二维材料和纳米电子器件提供了理论依据.     

Optoelectronic and thermoelectric properties of Zintl YLi3X2(X=Sb,Bi) compounds through modified Becke—Johnson potential

In the present work, we investigate the structural, optoelectronic and thermoelectric properties of the YLi₃X₂(X=Sb, Bi) compounds using the full potential augmented plane wave plus local orbital (FP-APW+lo) method. The exchange-correlation potential is treated with the generalized gradient approximation/local density approximation (GGA/LDA) and with the modified Becke-Johnson potential (TB-mBJ) in order to improve the electronic band structure calculations. In addition, the estimated ground state properties such as the lattice constants, external parameters, and bulk moduli agree well with the available experimental data. Our band structure calculations with GGA and LDA predict that both compounds have semimetallic behaviors. However, the band structure calculations with the GGA/TB-mBJ approximation indicate that the ground state of the YLi₃Sb₂ compound is semiconducting and has an estimated indirect band gap (Γ-L) of about 0.036 eV while the ground state of YLi₃Bi₂ compound is semimetallic. Conversely the LDA/TB-mBJ calculations indicate that both compounds exhibit semiconducting characters and have an indirect band gap (Γ-L) of about 0.15 eV and 0.081 eV for YLi₃Sb and YLi₃Bi₂ respectively. Additionally, the optical properties reveal strong responses of the herein materials in the energy range between the IR and extreme UV regions. Thermoelectric properties such as thermal conductivity, electrical conductivity, Seebeck coefficient, and thermo power factors are also calculated.     

Electronic structure of collapsed C,BN, and BC3 nanotubes

The electrical properties of single-wall C, BN, and BC₃ nanotubes in ideally rolled-up forms show a wide spectrum from truly metals to large band gap semiconductors. In the presence of radial deformations that collapse tubes, the electrical properties are severely modified such that metals turn into semiconductors and vice versa. Based on first-principles pseudopotential calculations, we find that metallic C nanotubes have a finite band gap if radial deformations break all mirror symmetries of the tubes, and that original finite gaps (∼0.5 eV) of semiconducting C and BC₃ tubes are closed by collapsing deformations. In BN tubes, band gaps can be tuned in the range 2–5 eV. On the other hand, the band gaps of armchair BN and zigzag BC₃ nanotubes are found to be insensitive to radial deformations. These new findings can be applied to design new types of nanotube-based functional devices using radial deformations.     

应变对两层半氢化氮化镓薄膜电磁学性质的调控机理研究

采用基于密度泛函理论的第一性原理模拟计算,研究了在应变作用下两层半氢化氮化镓纳米薄膜的电学和磁学性质.没有表面修饰的两层氮化镓纳米薄膜的原子结构为类石墨结构,并具有间接能隙.然而,当两层氮化镓纳米薄膜的一侧表面镓原子被氢化时,该纳米薄膜却依然保持纤锌矿结构,并且展示出铁磁性半导体特性.在应变作用下,两层半氢化氮化镓纳米薄膜的能隙可进行有效调控,并且它将会由半导体性质可转变为半金属性质或金属性质.这主要是由于应变对表面氮原子的键间交互影响和p-p轨道直接交互影响之间协调作用的结果.该研究成果为实现低维半导体纳米材料的多样化提供了有效的调控手段,为其应用于新型电子纳米器件和自旋电子器件提供重要的理论指导.     

First-principles study of zinc-blende to rocksalt phase transition in BN

The structural, electronic and elastic properties of the cubic boron nitride (BN) compound are investigated by a first-principle pseudopotential method. The calculations show that the structural phase transition from the zinc-blende(ZB) structure to the rocksalt (RS) structure occurs at a transition pressure of 1088 GPa and with a volume reduction of 3.1%. Both the ZB and RS structures of BN have indirect gaps, with energy gaps of 4.80 eV and 2.11 eV, respectively. The positive pressure derivative of the indirect band gap (Γ-X) energy for the the ZB phase and the predicted ultrahigh metallization pressure are attributed to the absence of d occupations in the valence bands. The increase of the shear modulus with increasing pressure implies that the lattice stability becomes higher when BN is compressed.     

Band Gap Adjustment of SiC Honeycomb Structure through Hydrogenation and Fluorination

Previous calculations show that the two-dimensional(2 D) silicon carbide(SiC) honeycomb structure is a structurally stable monolayer. Following this, we investigate the electronic properties of the hydrogen and fluorine functionalized SiC monolayer by first-principles calculations. Our results show that the functionalized monolayer becomes metallic after semi-hydrogenation or semi-fluorination, while the semiconducting properties are obtained by the full functionalization. Compared with the bare SiC monolayer, the band gap of the fully hydrogenated system is increased, in comparison with the decrease of the gap in the fully fluorinated case. As a result, the band gap can be tuned from 0.73 to 4.14 eV by the functionalization. In addition to the metal-semiconductor transition, hydrogenation and functionalization also realize a direct-indirect semiconducting transition in the 2 D SiC monolayer. These results provide theoretical guidance for design of photoelectric devices based on the SiC monolayer.