First principles calculations of the structural and electronic properties of(CdSe)n clusters

The structural and electronic properties of (CdSe)n(1≤n≤5) clusters are calculated using density functional theory within the pseudopotential and generalized gradient approximations. The calculated binding energies and highest occupied molecular orbital lowest unoccupied molecular orbital gaps are compared with those obtained within local density approximation.     

Ab initio study of structural, electronic and optical properties of MnHg(SCN)4 and FeHg(SCN)4

 The structural, electronic and optical properties of MnHg(SCN)₄ and FeHg(SCN)₄ were studied by means of quantum-mechanical calculations based on the density-functional theory and pseudopotential method. The lattice constants can be compared with the experimental values when the effects of temperature are considered. The peaks of partial density of states of S, C, N and Hg of FeHg(SCN)₄ have a tendency of shifting to the higher energy levels relative to those of MnHg(SCN)₄. The distributions of the 3d electronic states in the transition metal atoms show quite large difference and decide different optical properties. We found that absorptional peaks of FeHg(SCN)₄ lag behind those of MnHg(SCN)₄ and the peak in the infrared range has a higher absorptional intensity, which are in accord with the experimental results. By analyzing the distributions and transitions of the 3d electronic states, we explained the different absorption phenomena.     

The Electric Field Gradient of 111Ag in Macrocyclic Crown Thioethers

Time differential perturbed angular correlation experiments and ab-initio density functional theory calculation were used to determine the electric field gradients of the metal centres of the macrocyclic crown thioethers Ag(15S5)[BF₄], Ag(18S6-CH₂OH)[CF₃SO₃], Ag(18S6)⁺, Ag(19S6-OH)[Tosylat] and Ag(20S6-OH)[CF₃SO₃]. The density functional theory calculations have been performed with the Amsterdam Density Functional code ADF. A “fingerprint system” is introduced, which allows to assign electric field gradients to certain Ag coordinations in these crown thioether complexes.     

四种耐热含能化合物电子结构的第一性原理研究

本文模拟计算了2,2’,4,4’,6,6’-六硝基联苯(HNBP)、2,2’,4,4’,6,6’-六硝基二苯乙烯(HNS)、2,5-二苦基-1,3,4-噁二唑(DPO)和5,5''-双(2,4,6-三硝基苯基)-2,2''-双(1,3,4-噁二唑)(TKX-55)四种耐热含能化合物的分子结构、Mulliken电荷布居、分子静电势(MEP)和Hirshfeld表面, 通过研究其分子特性、电子特性以及分子间相互作用, 以了解高耐热性含能化合物的耐热机理. 结果表明, 桥连接结构的复杂性以及分子间强氢键相互作用会增强含能化合物的稳定性. 此外, 本研究还发现中间基团的加入会对四种含能化合物分子两侧芳香环上碳原子的电荷分布以及分子表面正负静电势区域面积产生一定的影响.     

Investigation of electronic,elastic, and optical properties of topological electride Ca_3Pb via first-principles calculations

Electrides are unique materials with the anionic electrons confined to the interstitial sites, expecting important applications in various areas. In this work, the electronic structure and detailed physical properties of topological electride Ca_3Pb are studied theoretically. By comparing the crystal structures and band structures of Ca_3Pb and Ca_3Pb O, we find that after removing O_2-ions from Ca_3Pb O, the remaining electrons are confined in the vacancies of the Ca_6 octahedra centers,playing the role as anions and forming an additional energy band compared with that of Ca_3Pb. These interstitial electrons partially result in the low work function of Ca_3Pb. Moreover, the calculated mechanic properties imply that Ca_3Pb has a strong brittleness. In addition, the dielectric functions and optical properties of Ca_3Pb are also analyzed.     

A metal-semiconductor transition triggered by atomically flat zigzag edge in monolayer transition-metal dichalcogenides

Due to the structure of three stacked layers, monolayer transition-metal dichalcogenides (TMDs) is different from graphene. Creating atomically flat graphene-like edges in them has long been expected, which is crucial to the modulation of electronic structures in two-dimensional systems. Recently, by thermal annealing, Chen et al. [21] successfully synthesized atomically flat Mo-terminated edge in monolayer MoS₂. Inspired by this, through first-principles calculations, we studied the electronic and transport properties of typical TMD monolayers with transition atom-terminated flat zigzag edges, i.e., ScS₂, VS₂, CrS₂, FeS₂, NiS₂, MoS₂ and WS₂. It is found that the nanoribbons with and without flat edges are both metallic. Interestingly, the vacancy in the flat edge could open a transmission gap at the Fermi level in the ScS₂ ribbon, and trigger a metal-semiconductor transition. Further analysis shows that, the opening of bandgap around the Fermi level induced by the specific pattern of vacancies is the mechanism behind, which could be used as an modulating method for electronic structures. We believe our results are quite beneficial for the development of many other monolayer transition-metal dichalcogenides configurations, showing great application potential.     

Structure, electronic and magnetic properties of Cr-doped (ZnS)12 clusters: A first-principles study

We have studied the structural, electronic, and magnetic properties of (ZnS)₁₂ clusters doped with one (monodoped) and two (bidoped) Cr atoms in terms of a first-principles method. Substitutional, exohedral, and endohedral doping are considered. The substitutional isomer is found to be most favorable in energy for monodoped clusters, while the exohedral isomers are found to be most favorable for bidoped clusters. The magnetic coupling between the Cr atoms is mainly governed by the competition between direct Cr-Cr antiferromagnetic (AFM) interaction and the ferromagnetic (FM) interaction between two Cr atoms via S atom due to strong p-d hybridization. Finally, we show that the exohedral bidoped (ZnS)₁₂ clusters favor the FM state, which has potential applications in nanoscale quantum devices.     

Cd、Sr掺杂Mg2Ge电子结构和光学性质的第一性原理研究

此文用基于密度泛函理论(DFT)的第一性原理计算方法,分别研究了本征、掺Cd、掺Sr的Mg₂Ge的能带结构、电子态密度和光学性质.研究结果表明,本征Mg₂Ge是一种间接带隙半导体,带隙值为0.228eV.Sr的掺入使其变成带隙为0.591 eV的直接带隙半导体,Cd掺杂Mg₂Ge后表现出半金属性质.掺杂后的主要吸收峰减小,吸收谱范围增加.在可见光能量范围内,掺杂的Mg₂Ge有更低的反射率,对可见光的利用率增强.此外,掺杂还提高了高能区的光电导率.     

Half-Heusler合金Cu1-xFexMnSb的电子结构和反铁磁-铁磁相变

基于密度泛函理论（DFT）,使用局域密度近似（LDA）研究了Heusler合金Cu1-xFexMnSb的电子结构和反铁磁-铁磁相变。研究发现,两种磁状态下的合金晶格常数随掺杂浓度x变化很好地满足Vegard定理。当x>0.5时,铁磁态合金的总磁矩很好地符合SP规律,然而当x<0.5时,却发生了明显的偏离。由于整个体系存在RKKY和超交换磁耦合的竞争,因而在x=0.25时,我们观察到了独特的反铁磁—铁磁相变。进一步的态密度分析发现,Cu的掺杂浓度可以有效调整铁磁态合金的费米面位置,并且反铁磁态合金由于不同自旋方向的Mn原子的分波态密度相互补偿,总态密度形成了几乎完全对称的自旋向上带和自旋向下带。     

Half-Heusler合金Cu1-xFexMnSb的电子结构和反铁磁-铁磁相变简

基于密度泛函理论(DFT),使用局域密度近似(LDA)研究了Heusler合金Cu1-xFex MnSb的电子结构和反铁磁-铁磁相变.研究发现,两种磁状态下的合金晶格常数随掺杂浓度x变化很好地满足Vegard定理.当x0.5时,铁磁态合金的总磁矩很好地符合SP规律,然而当x0.5时,却发生了明显的偏离.由于整个体系存在RKKY和超交换磁耦合的竞争,因而在x=0.25时,我们观察到了独特的反铁磁—铁磁相变.进一步的态密度分析发现,Cu的掺杂浓度可以有效调整铁磁态合金的费米面位置,并且反铁磁态合金由于不同自旋方向的Mn原子的分波态密度相互补偿,总态密度形成了几乎完全对称的自旋向上带和自旋向下带.     

Theoretical study on the electronic structures and properties of diindolocarbazole isomers

The objective of this work is to provide an in‐depth interpretation of the electronic structures and optical properties of diindolocarbazole isomers. A systematic study of these different structures caused by the linkage pattern was performed via theoretical calculations. The optimized geometries, electronic properties, frontier molecular orbitals, ionization potentials, electron affinities, reorganization energies, and absorption and emission spectra of these isomers have been calculated and analyzed. Based on the detailed comparisons, the diindolocarbazoles act as candidates of different functional materials for optoelectronic application was predicted and the theoretical reference for the synthesis efforts and experimental investigation was provided. Copyright © 2014 John Wiley & Sons, Ltd.     

Pressure effects on structural,elastic and electronic properties of BaZnO2: first-principles study

The structural, elastic and electronic properties of BaZnO₂ under pressure are investigated by the plane wave pseudopotential density functional theory (DFT). The calculated lattice parameters and unit cell volume of BaZnO₂ at the ground state are in good agreement with the available experimental data and other theoretical data. The pressure dependences of elastic constants C_ij, bulk modulus B, shear modulus G, B/G, Poisson’ s ratio σ, Debye temperature Θ and aggregate acoustic velocities V_P and V_S are systematically investigated. It is shown that BaZnO₂ maintains ductile properties under the applied pressures. Analysis for the calculated elastic constants has been made to reveal the mechanical stability and mechanical anisotropy of BaZnO₂. At the ground state, the calculated compressional and shear wave velocities are 8.26 km/s and 1.81 km/s, respectively, and the Debye temperature Θ is 240.8 K. The pressure dependences of the density of states and the bonding property of BaZnO₂ are also investigated.     

Structural and electronic properties of a single C chain doped zigzag BN nanoribbons

The effects of single C-chain on the stability, structural and electronic properties of zigzag BN nanoribbons (ZBNNRs) were investigated by first-principles calculations. C-chain was expected to dope at B-edge for all the ribbon widths _Nz$N_z$ considered. The band gaps of C-chain doped _Nz$N_z$-ZBNNR are narrower than that of perfect ZBNNR due to new localized states induced by C-chain. The band gaps of _Nz$N_z$-ZBNNR-C(n  ) are direct except for the case of C-chain position n=2$n=2$. Band gaps of BN nanoribbons are tunable by C-chain and its position n, which may endow the potential applications of BNNR in electronics.     

Electronic structure and optical properties of non-metallic modified graphene: a first-principles study

In this paper, the electronic structure and stability of the intrinsic, B-, N-, Si-, S-doped graphene are studied based on first-principles calculations of density functional theory. Firstly, the intrinsic, B-, N-, Si-, S-doped graphene structures are optimized, and then the forming energy, band structure, density of states, differential charge density are analyzed and calculated. The results show that B- and Si-doped systems are p-type doping, while N is n-type doping. By comparing the forming energy, it is found that N atoms are more easily doped in graphene. In addition, for B-, N-, Si-doped systems, it is found that the doping atoms will open the band gap, leading to a great change in the band structure of the doping system. Finally, we systematically study the optical properties of the different configurations. By comparison, it is found that the order of light sensitivity in the visible region is as follows: S-doped> Si-doped> pure > B-doped > N-doped. Our results will provide theoretical guidance for the stability and electronic structure of non-metallic doped graphene.     

气相中Fe+催化CO与N2O循环反应的理论计算研究

采用密度泛函UB3LYP/6–311+G(2d)方法计算研究了Fe+在基态和激发态与CO与N2O反应的反应机理。全参数优化了反应势能面上各驻点的几何构型,用频率分析方法和内禀反应坐标（IRC）方法对过渡态进行了验证,并用UB3LYP/6–311++G(3df,3pd)、单点垂直激发等方法分别进行各驻点单点能校正,四重态和六重态反应势能面交叉点CP确定,计算结果表明,该反应为两步反应,且反应机理都为插入—消去反应,势能面上的两个交叉点能够有效的降低反应的活化能,这在动力学和热力学上都是有利的。     

Structural,elastic, electronic,andoptical properties of layered TiNX (X = F,Cl, Br,I) compounds: a density functional theory study

ABSTRACT

Titanium nitride halides, TiNX (X = F, Cl, Br, I) in the α-phase (orthorhombic) are exciting quasi two-dimensional (2D) electronic systems exhibiting a fascinating series of electronic ground states. Pristine TiNX are semiconductors with varying energy gaps and possess attractive properties for potential applications in optoelectronics, photovoltaics, and thermoelectrics. Alkali metal intercalated TiNCl becomes superconducting at reasonably high temperature. We have revisited the electronic band structure of TiNX using density functional theory (DFT) based calculations. The atomic orbital resolved partial electronic energy densities of states are calculated together with the total density of states (TDOS). The structural and elastic properties have been investigated in details for the first time. The elastic anisotropy has been explored. The optical properties of TiNX are studied for the first time. The Debye temperatures have been calculated and the related thermal and phonon parameters are discussed. The calculated physical parameters are compared with existing theoretical and experimental results and showed fair agreement. TiNX are found to reflect electromagnetic radiation strongly in the mid ultraviolet region. The elastic properties show high degree of anisotropy. The effect of halogen atoms on various structural, elastic, electronic, and thermal properties in TiNX are also discussed in detail.     

ZnSe小团簇结构稳定性和电子性质研究

文章研究了小尺寸的(ZnSe)n团簇(n=2-16)的结构和电子性质.通过手工搭建得到团簇结构,用DMol软件包进行结构优化和能量计算,最后分析计算结果 .研究结果表明,对于n=2-4,平面环状结构的能量最低;对于n=5,非平面环状结构的能量最低;对于n=6-12,空心笼状结构的能量最低;对于n=13,核-壳笼状结构的能量最低;对于n=14-16,依旧是空心笼状结构的能量最低.通过分析(ZnSe)_n团簇(n=2-16)的电子性质,我们可以得到,(ZnSe)_9团簇、(ZnSe)_(12)团簇具有很好的稳定性.     

缺陷碳纳米管限域金属Ti原子的理论研究

基于密度泛函第一性原理研究了金属原子Ti在原始、单空位缺陷(SV)、Stone-Wales(SW)缺陷碳纳米管内外的吸附情况.我们的计算结果表明金属Ti原子在缺陷碳纳米管内外结合能的排列顺序为:SVSW-zSW-xpristine(外吸附),SVSW-xSW-zpristine(内吸附).同时,我们通过吸附结构、电子密度和态密度等分析了Ti原子与碳纳米管的作用机制.其中,SV缺陷碳纳米管由于失去一个碳原子而形成了的三个悬键具有很强的结合能力,金属原子Ti在SV缺陷碳纳米管内外的吸附能力都是最强的.对于SW缺陷的碳纳米管,由于缺陷的位置不同,对于金属原子Ti内外吸附的能力也是不同的.因此,缺陷的存在能调节碳纳米管载体对Ti原子的吸附性能.     

First-principles study on the structural and electronic properties of LiB and its hydrides (Li2BnHn, n=5, 8, 12, LiBH4)

Structural, electronic and vibrating properties of LiB and its hydrides (Li₂B_nH_n, n=5, 8, 12, LiBH₄) were calculated by the first-principles using density functional theory in its generalized gradient approximation. The calculated results are in good agreement with experimental studies. The deviation between theory and experimental results are also discussed. With the increasing of H atoms in range of 5-12, the band gap energy increases and the width of the conduction band decreases. Comparing with LiB, the band gap of LiBH₄ is broadened, which indicates the enhancement of Li-B and Li-H bond strength. Valence electrons mainly transfer from Li atoms to B and H atoms. As a result, Li atoms are thought to be partially ionized as Li⁺ cations. There is little contribution of Li orbital to the occupied states, resulting in Li-H and Li-B bond exhibiting an ionic nature, and B-H bond showing a covalent nature.