5d过渡金属原子吸附氮化硼纳米管的第一性原理计算

采用基于密度泛函理论的第一性原理计算方法,研究了氮化硼纳米管六元环中心吸附5d过渡金属原子后体系的几何结构,电子结构和磁性性质.研究发现,吸附原子向一个氮原子或硼原子偏移;吸附体系在费米能级附近出现明显的杂质能级;各个体系的总磁矩随原子序数出现规律性变化,局域磁矩主要分布在吸附原子上.     

5d过渡金属原子掺杂氮化硼纳米管的第一性原理计算

采用基于密度泛函理论的第一性原理计算方法,研究了当氮化硼纳米管（BNNT）中的B原子和N原子被5d过渡金属原子（Lu,Hf,Ta,W,Re,Os,Ir,Pt,Au,Hg）取代时BNNT的几何结构、电子结构和磁性性质. 作为对比,给出了理想BNNT,B缺陷体系（V_B）和N缺陷体系（V_N）的相应结果. 研究发现：5d原子取代B（B_5d）时体系的局域对称性接近于C_3v,但是取代N（N_5d）时体系的局域对称性偏离C_3v对称性较大;利用相同的5d原子进行掺杂时,B_5d的成键能比N_5d的成键能大;对于B_5d或者N_5d,其成键能基本上随着5d原子的原子序数的增大而降低;掺杂体系中出现了明显的杂质能级,给出了态密度等结果;不同掺杂情况的磁矩不同,取代B 时体系的总磁矩呈现出较强的规律性. 利用对称性和分子轨道理论解释了5d原子取代B时杂质能级的产生和磁性的变化规律. 关键词： 第一性原理计算 5d过渡金属原子 氮化硼纳米管 密度泛函理论     

5d过渡金属原子掺杂氮化铝纳米管电子结构、磁性性质的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理计算方法, 研究了5d过渡金属原子(Lu、Hf、Ta、W、Re、Os、Ir、Pt、Au、Hg)取代AlN纳米管(AlNNTs)中的铝原子或氮原子时体系的几何结构、电子结构和磁性性质; 并且以理想AlN纳米管(AlNNTs)、Al缺陷体系(VAl)和N缺陷体系(VN)的结果作为对比. 研究发现: 5d 原子取代Al(Al5d)时体系的局域对称性接近于C3v, 但是取代N(N5d)时体系的局域对称性偏离C3v对称性较大; 当掺杂的5d元素相同时, Al5d的成键能比N5d的成键能大; 当掺杂体系相同时(Al5d或N5d), 其成键能基本上随着5d原子的原子序数的增大而降低; 掺杂体系中出现了明显的杂质能级, 给出了态密度等结果; 不同掺杂情况的磁矩不同, 总磁矩呈现出较强的规律性. 利用C3v对称性和分子轨道理论解释了过渡金属原子取代Al时杂质能级的产生和体系磁性的变化规律.     

5d过渡金属原子掺杂氮化铝纳米管电子结构、磁性性质的第一性原理计算

采用基于密度泛函理论(DFT)的第一性原理计算方法, 研究了5d过渡金属原子(Lu、Hf、Ta、W、Re、Os、Ir、Pt、Au、Hg)取代AlN纳米管(AlNNTs)中的铝原子或氮原子时体系的几何结构、电子结构和磁性性质; 并且以理想AlN纳米管(AlNNTs)、Al缺陷体系(VAl)和N缺陷体系(VN)的结果作为对比. 研究发现: 5d 原子取代Al(Al5d)时体系的局域对称性接近于C3v, 但是取代N(N5d)时体系的局域对称性偏离C3v对称性较大; 当掺杂的5d元素相同时, Al5d的成键能比N5d的成键能大; 当掺杂体系相同时(Al5d或N5d), 其成键能基本上随着5d原子的原子序数的增大而降低; 掺杂体系中出现了明显的杂质能级, 给出了态密度等结果; 不同掺杂情况的磁矩不同, 总磁矩呈现出较强的规律性. 利用C3v对称性和分子轨道理论解释了过渡金属原子取代Al时杂质能级的产生和体系磁性的变化规律.     

5d过渡金属二硼化物的结构和热、力学性质的第一性原理计算

利用基于密度泛函理论的第一性原理系统地研究了5d过渡金属二硼化物TMB₂ (TM=Hf–Au) 的结构、热学、力学和电学性质. 我们考虑了三种结构, 分别为AlB₂, ReB₂和WB₂结构. 计算得到的晶格常数与先前的理论和实验研究符合得很好. 通过计算生成焓预测了化合物的热力学稳定性; 从HfB₂到AuB₂, 生成焓的整体趋势是逐渐增加的. 在所考虑的结构中, 对HfB₂和TaB₂, AlB₂结构是最稳定的; 对WB₂, ReB₂, OsB₂, IrB₂和AuB₂, ReB₂结构是最稳定的; 对PtB₂, WB₂结构是最稳定的. 在所考虑的化合物中, ReB₂结构的ReB₂具有最大的剪切模量(295 GPa), 是最硬的化合物, 与先前的理论和实验结果相符. 计算得到的总态密度显示所有结构都具有金属特性. 讨论了系列化合物的变化趋势. 关键词： 弹性性质 热力学性质 第一性原理 5d过渡金属二硼化物     

P掺杂单壁硅纳米管Mg原子吸附性能的第一性原理研究

采用密度泛函理论的广义梯度近似和平面波赝势方法,研究P掺杂单壁硅纳米管对Mg原子的吸附性能.计算本征、掺杂P、施加形变作用（压缩和拉伸）的（6,6）硅纳米管外壁对Mg原子的吸附能,分析掺杂P前后的成键情况及电荷布局数.结果表明,掺杂P使体系形成Mg-P和Si-P间的离子性键,增强了Si-Si间的离子性键,P掺杂硅纳米管超晶格中离子键与共价键共存;掺杂P后显著提高了硅纳米管外壁对Mg原子的吸附能力;硅纳米管外壁对Mg原子的吸附能在0.25%,0.50%,1.00%,1.25%的压缩量和1.00%,1.25%的拉伸量时增大,可显著增强硅纳米管材料作为增强相时与基体界面间结合的粘附性.     

He原子在金属Ti中行为的第一性原理计算

采用基于量子化学基本原理的密度泛函理论，研究He原子在金属T冲的占位、能量及结构优化后材料各性质参数的变化情况，以及He原子聚集成泡的微观原因。     

过渡金属氮化物中单原子固溶和力学性能的第一性原理研究

基于密度泛函理论(DFT)的第一性原理,计算Si原子在Ti族和V族氮化物中以及B、C和Ge原子在TiN晶体中固溶的稳定结构,讨论置换型和间隙型固溶的低能量稳定结构与晶体间距的关系,研究金属氮化物和固溶原子固溶结构的力学性能.结果表明:Si原子在TiN、ZrN、HfN和TaN晶体中固溶以及Ge原子在TiN晶体中固溶情况为,单原子不进入对应过渡金属氮化物晶体中形成间隙固溶或置换固溶,随着晶体间距离变化单原子可以在晶体之间形成间隙固溶或置换固溶;Si原子在NbN以及B原子在TiN晶体中可以实现间隙固溶,而不能形成置换固溶;Si原子在VN和C原子在TiN晶体中固溶结构形式均为置换固溶.单原子固溶形成低能量置换型固溶体和间隙型固溶体的弹性常数、体模量和剪切模量均低于原过渡金属氮化物的对应值.     

氧、硫掺杂六方氮化硼单层的第一性原理计算

采用基于密度泛函理论和投影缀加平面波的第一性原理计算方法, 研究了六方氮化硼单层(h-BN)中的氮原子缺陷(V_N)、氧原子取代氮原子(O_N)和硫原子取代氮原子(S_N)时的几何结构、磁性性质和电子结构.研究发现, V_N和O_N体系形变较小, 而S_N体系形变较大; h-BN本身无磁矩, 但具有N缺陷或者掺杂后总磁矩都是1 μ_B; 同时给出了态密度和能带结构.利用掺杂体系的局域对称性和分子轨道理论解释了相关结果, 尤其是杂质能级和磁矩的产生. 关键词： 六方BN单层 第一性原理计算 密度泛函理论 分子轨道理论     

原子分子在Ni(100)表面吸附的第一性原理研究

本文采用密度泛函理论,结合周期性平板模型,通过对原子H、N、O、S和C,分子CO、N2、NH3、NO,以及自由基CH3、CH、CH2、OH在Ni(100)表面吸附的研究,比较了它们的吸附能,稳定吸附位点,吸附结构及扩散能垒等信息.这些吸附质与表面结合能力从小到大依次是N2NH3COCH3NOHOHCH2CNSONCHC.在所有的原子中,O原子倾向于吸附在桥位,而其余的原子则倾向于吸附在空位.除N2之外的分子吸附物(CO、NO、NH3),最佳吸附位点均为四重空位,而N2的最稳定吸附位置为顶位.对于自由基吸附物(CH、CH2、CN、OH)而言,它们倾向于吸附在四重空位,而CH3则稳定吸附在桥位.     

First principle study of unzipped boron nitride nanotubes

Systematic first principle calculations have been used to explain the dangling bonds behaviour in the rolling up of a boron nitride nanoribbon (BNNR) to construct a single-walled boron nitride nanotube (BNNT). We found in armchair BNNR two degenerate dangling bonds split and move up to higher energies due to symmetry breaking of system. While in zigzag BNNR changing the topology of system does not affect on metallic features of the band structure, but in unzipped BNNT case a metallic-semimetallic phase transition occurs. Considering the width dependent electronic properties of hydrogen passivated armchair BNNRs, exhibit zigzag behaviour of energy gap in agreement with previous results.     

Selectively strong molecular adsorption on boron nitride monolayer induced by transition metal substrate

We studied adsorption of several molecules (CO, CO₂, H₂O, N₂O, NO, NO₂, and O₂) on hexagonal boron nitride (h-BN) monolayers supported on transition metal (TM) surfaces, using density functional calculations. We observed that all the molecules bind very weakly on the pristine h-BN, with binding energies in the range of 0.02–0.03 eV. Interestingly, however, when h-BN is supported on the TM surface, NO₂ and O₂ become strongly chemisorbed on h-BN, with binding energies of >1 eV, whereas other molecules still physisorbed, with binding energies of ～0.1 eV at most. The electron transfer from TM to p_z states of h-BN played a substantial role in such strong bindings of NO₂ and O₂ on h-BN, as these molecules possess unpaired electrons that can interact with p_z states of h-BN. Such selective molecular binding on h-BN/TM originates from the peculiar distribution of the spin-polarized highest occupied and lowest unoccupied molecular orbitals of NO₂ and O₂. Strong molecular adsorption and high selectivity would make the h-BN/TM system possible for a variety of applications such as catalysts and gas sensors.     

Electronic properties of C-doped boron nitride nanotubes studied by first-principles calculations

The geometry and electronic structure of C-doped BNNTs are investigated using the hybrid Heyd–Scuseria–Ernzerhof. The van Hove singularity (vHs) peaks split in density of states (DOS) The impurity states decrease the bandgap.

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A DFT study for adsorption of CO on Ni,Pd and Pt atoms doped (7, 0) boron nitride nanotube

By using density functional theory calculations, we investigated the structural, electronic and magnetic properties of carbon monoxide (CO) adsorption on the pure, Ni, Pd and Pt doped atoms in zigzag single-walled (7, 0) boron nitride nanotubes (BNNTs). The results indicated that compared to the pure (7, 0) BNNTs, replacing B atom by Ni, Pd and Pt atoms can significantly increase the adsorption energy of CO gas on the BNNTs. The adsorption energies of CO gas on the pure (7, 0) Ni, Pd and Pt doped (7, 0) BNNTs are ?0.2013, ?1.746, ?1.593 and ?2.257 eV, respectively. Our results revealed that in comparison with the pure (7, 0) BNNTs, CO gas is chemisorbed on the transition metal doped (7, 0) BNNTs with the appreciable adsorption energy. In addition, it was found that by doping these atoms, band gap energy of the pure (7, 0) BNNTs is considerably decreased. These observations suggested that the Pt doped (7, 0) BNNTs can be introduced as a promising candidate in gas sensor devices for detecting CO gas.     

Boron nitride nanotubes with quadrangular cross sections: Density functional studies

Density functional theory (DFT) calculations have been performed to investigate the availabilities and properties of boron nitride nanotubes (BNNTs) with quadrangular cross sections. To achieve the purposes, the original structure of a representative BNNT was individually decorated by the carbon and silicon atoms to make the C-BNNT and Si-BNNT models. The sp³ hybridizations were set for the C and Si atoms to make possible the formation of the quadrangular cross sections for the BNNTs. The optimized results indicated that the investigated models could be stabilized; however, they showed different properties. The atomic scale properties based on computations of quadrupole coupling constants (C_Q) also approved different properties for the C-BNNT and Si-BNNT models. Moreover, the C_Q parameters indicated that the properties of C-BNNT could be considered similar to the original BNNT; however, more discrepancies were observed for the Si-BNNT.     

Adsorption of HCN molecules on Ni,Pd and Pt-doped (7, 0) boron nitride nanotube: a DFT study

We studied affinity of pure and Ni, Pd and Pt-doped (7, 0) boron nitride nanotubes (BNNTs) to toxic HCN molecules using density functional theory calculations. The results indicated that the pure (7, 0) BNNTs can weakly adsorb HCN molecules with adsorption energy of ?0.2474 eV. Upon adsorption of HCN molecules on this nanotube, the band gap energy was decreased from 3.320 to 2.960 eV. The more negative adsorption energy between these transition metal-doped (7, 0) BNNTs and HCN molecules indicated that doping of (7, 0) BNNTs with Ni, Pd and Pt elements can significantly improve the affinity of BNNTs toward this gas. Additionally, it was found that the interaction energy between HCN molecules and Pt-doped BNNTs is more negative than those of the Ni and Pd-doped BNNTs. These observations suggested that the Pt-doped (7, 0) BNNTs are strongly sensitive to HCN molecules and therefore it may be used in gas sensor devices for detecting this toxic gas.     

First principles study of structural and electronic properties of different phases of boron nitride

A theoretical study of structural and electronic properties of the four phases of BN (zincblende, wurtzite, hexagonal and rhombohedral) is presented. The calculations are done by full potential (linear) augmented plane wave plus local orbitals (APW+lo) method based on the density functional theory (DFT) as employed in WIEN2k code. Using the local density approximation (LDA) and generalized gradient approximation (GGA-PBE) for the exchange correlation energy functional, we have calculated lattice parameters, bulk modulus, its pressure derivative and cohesive energy. In order to calculate electronic band structure, another form of the generalized gradient approximation proposed by Engel and Vosko (GGA-EV) has been employed along with LDA and GGA-PBE. It is found that all the three approximations exhibit similar band structure qualitatively. However, GGA-EV gives energy band gap values closer to the measured data. Our results for structural and electronic properties are compared with the experimental and other theoretical results wherever these are available.     

Structure,electronic and magnetic properties of hexagonal boron nitride sheets doped by 5d transition metal atoms: First-principles calculations and molecular orbital analysis

A first-principles calculation based on density functional theory is carried out to reveal the geometry, electronic structures and magnetic properties of hexagonal boron nitride sheets (h-BNSs) doped by 5d transitional mental atoms (Lu, Hf, Ta, W, Re, Os, Ir, Pt, Au and Hg) at boron-site (B_5d) and nitrogen-site (N_5d). Results of pure h-BNS, h-BNS with B vacancy (V_B) and N vacancy (V_N) are also given for comparison. It is shown that all the h-BNSs doped with 5d atoms possess a C_3v local symmetry except for N_Lu and N_Hg which have a clear deviation. For the same 5d dopant, the binding energy of B_5d is larger than that of N_5d, which indicates the substitution of a 5d atom for B is preferred. The total densities of states are presented, where impurity energy levels exist. Besides, the total magnetic moments (TMMs) change regularly with the increment of the 5d atomic number. Theoretical analyses by molecular orbital under C_3v symmetry explain the impurity energy levels and TMMs.