B12-nAlnN12 (n=0, 6, 12) 的稳定性和电子结构研究

通过Al取代B在B12N12中掺杂,基于密度泛函理论对B6Al6N12的稳定性进行了系统研究．表明在B6Al6N12中,Al和B倾向于相对分开．在最稳定结构中,B原子和Al原子分别处在笼的两半．我们还分析了B12-nAlnN12 (n=0, 6, 12)的电子结构,B12N12的能隙为6.84eV,掺Al后其能隙明显变窄,Al12N12和B6Al6N12的能隙分别为3.91eV和4.08eV．NBO分析表明,B12N12中B/N原子的电荷分别为±1.17,Al12N12中Al/N 原子的电荷分别为±1.85．在B6Al6N12中,B/Al原子上的电荷分别为1.06~1.12和1.86~1.91,N原子上的电荷为-1.18~-1.83．     

B12-nAlnN12 (n=0, 6, 12) 的稳定性和电子结构研究

通过Al取代B在B12N12中掺杂,基于密度泛函理论对B6Al6N12的稳定性进行了系统研究．表明在B6Al6N12中,Al和B倾向于相对分开．在最稳定结构中,B原子和Al原子分别处在笼的两半．我们还分析了B12-nAlnN12 (n=0, 6, 12)的电子结构,B12N12的能隙为6.84eV,掺Al后其能隙明显变窄,Al12N12和B6Al6N12的能隙分别为3.91eV和4.08eV．NBO分析表明,B12N12中B/N原子的电荷分别为±1.17,Al12N12中Al/N 原子的电荷分别为±1.85．在B6Al6N12中,B/Al原子上的电荷分别为1.06~1.12和1.86~1.91,N原子上的电荷为-1.18~-1.83．     

Effects of bonded and non-bonded B/N codoping of graphene on its stability,interaction energy,electronic structure,and power factor

We model boron and nitrogen doped/codoped monolayer graphene to study its stability, interaction energy, electronic and thermal properties using density functional theory. It is found that a doped graphene sheet with non-bonded B or N atoms induces an attractive interaction and thus opens up the bandgap. Consequently, the power factor is enhanced. Additionally, bonded B or N atoms in doped graphene generate a repulsive interaction leading to a diminished bandgap, and thus a decreased power factor. We emphasis that enhancement of the power factor is not very sensitive to the concentration of the boron and nitrogen atoms, but it is more sensitive to the positions of the B or N atoms in ortho, meta, and para positions of the hexagonal structure of graphene. In the B and N codoped graphene, the non-bonded dopant atoms have a weak attractive interaction and interaction leading to a small bandgap, while bonded doping atoms cause a strong attractive interaction and a large bandgap. As a result, the power factor of the graphene with non-bonded doping atoms is reduced while it is enhanced for graphene with bonded doping atoms.     

C,N, O原子在金属V中扩散行为的第一性原理计算

基于密度泛函理论, 采用第一性原理计算方法研究了C, N, O原子在金属V中的扩散行为. 首先, 讨论了C, N, O原子在V体心立方晶格中的间隙占位情况, 分析了其在间隙位置与V晶格的相互作用, 并探究了这种相互作用对金属V电子结构的影响. 研究结果表明: C, N, O原子在V的八面体间隙位置更为稳定, 并且C, N, O原子的2p电子与V的3d电子之间有比较强的成键作用; C, N, O原子的扩散势垒分别为0.89, 1.26, 0.98 eV, 并得出了其扩散系数表达式; 最后, 通过阿仑尼乌斯关系图对比了三者在V中扩散系数的大小, 并计算出体系温度在500–1100 K之间时其在V中的扩散系数, 计算结果与实验值基本符合.     

Atomic N00N state generation in distant cavities by virtual excitations

A general scheme of generating N00N states of virtually-excited 2N atoms is proposed. The two cavities are fibre-connected with N atoms in each cavity. Although we focus on the case of N=2, the system can be extended to a few atoms with N>2. It is found that all 2N atoms can be entangled in the form of N00N states if the atoms in the first cavity are initially in the excited states and atoms in the second cavity are all in the ground states. The feasibility of the scheme is carefully discussed, it shows that the N00N state with a few atoms can be generated with good fidelity and the scheme is feasible in experiment.     

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.     

SrTiO3(001)表面上Au和N原子相互作用的第一性原理研究

采用基于密度泛函理论的第一性原理平面波赝势方法研究了SrTiO₃(001)表面上Au和N原子间相互作用的微观机理.通过比较分析N置换表面层O原子前后SrTiO₃(001)表面吸附Au原子体系的相关能量和电子结构,发现SrTiO₃(001)表面吸附Au原子和N替代表面层O原子的置换过程二者之间存在明显的"协同效应",即N原子置换SrTiO₃(001)表面层O原子的过程增强了相应表面吸附Au原子的稳定性,而SrTiO关键词： 表面结构 相互作用 第一性原理     

Fe中刃型位错上扭折及掺杂体系的电子结构

利用离散变分方法和DMol方法,研究了体心立方Fe中1/2［111］（110）刃型位错上扭折及掺杂（N,O）体系的电子结构.能量（杂质偏聚能及格位能）计算结果表明,杂质元素N,O进入扭折芯区的偏聚趋势,这与位错扭折引起的晶格畸变有关.同时,在杂质元素周围有一些电荷聚集,导致扭折上电荷的不均匀分布,杂质原子得到电子,其周围Fe原子失去电子.由于N原子的2p轨道与近邻Fe原子的3d4s4p轨道之间杂化,使N原子与近邻Fe原子间有较强的相互作用,不利于扭折的迁移,使位错运动受阻,有利于材料强度的提高;而O与最近邻Fe原子之间的相互作用较弱.杂质-扭折复合体的局域效应明显影响体系的电子结构、能量及性能. 关键词： 电子结构 刃型位错 扭折 杂质元素     

Optical second-harmonic generation study of incorporation of nitrogen atoms at Si(1 0 0) surfaces

The kinetics of N incorporation into Si layers has been studied on the Si(1 0 0) surface probing surface dangling bonds with an optical second-harmonic (SH) generation during surface exposure to N atoms generated by a radio frequency N₂ plasma. It is observed that SH intensity decreases with N dose. The rate of decrease in SH intensity apparently decreases with surface temperature, whereas total amount of N atoms taken on the surface remains constant. This fact suggests that N atoms are incorporated at the subsurface layers at higher temperatures. It is shown that the N incorporation at the subsurface layers proceeds by the indiffusion of N atoms either directly or indirectly via intermediate, metastable adsorption at the first surface layer. Applying Kisliuk adsorption model, activation energies of the N indiffusion are evaluated to be 0.30 ± 0.03 and 0.34 ± 0.05 eV for the indirect and direct path, respectively.     

Directed spontaneous emission from an extended ensemble of N atoms: timing is everything

A collection of static atoms is fixed in a crystal at a low temperature and prepared by a pulse of incident radiation of wave vector . The atoms are well described by an entangled Dicke-like state, in which each atom carries a characteristic phase factor exp(ik0.r(j)), where is the atomic position in the crystal. It is shown that a single photon absorbed by the N atoms will be followed by spontaneous emission in the same direction. Furthermore, phase matched emission is found when one photon is absorbed by N atoms followed by two-photon down-conversion.     

氮掺杂双层石墨烯吸附钠的第一性原理研究

采用密度泛函理论(DFT)的第一性原理方法,对Na在本征双层石墨烯(PBLG)和不同掺杂浓度的N掺杂石墨烯(NBLG)表面的吸附性质进行了研究.确定了不同N掺杂浓度时NBLG的最稳定N分布结构,计算了Na在PBLG和不同掺杂浓度的NBLG表面的吸附能.计算结果表明,N原子掺杂倾向于取代对位或次临近位置的C原子,并与下层C原子相对;随着N掺杂浓度的增加,吸附高度逐渐增加,且与掺杂N原子分布相匹配; Na在PBLG表面吸附使平均层间距增加,而在NBLG表面吸附使之减小; Na与C_(27)N_9表面的结合最稳定.     

Energetics and electronic properties of BN nanocones with pentagonal rings at their apexes

The geometric structures, energetics and electronic properties of the recently discovered BN nanocones are investigated using first-principles calculations based on the density-functional theory. We have proposed one particular structure for BN nanocones associated with the 240^° disclination, derived by the extraction of four 60^° segments, presenting as characteristic four pentagons at the apex and termination in two atoms. The cones are simulated by three clusters containing 58 B plus N atoms and additional 12 H atoms to saturate the dangling bonds at the edge. The most stable configuration is obtained when the two terminating atoms are one B and one N. For the cases where the two terminating atoms are of the same kind, the tip with B atoms is determined to have lower binding energy than with N atoms. The local densities of states of these BN nanocones are investigated and sharp states are found in the regions close (below and above) to the Fermi energy. Received 14 October 2002 / Received in final form 6 December 2002 Published online 11 February 2003 RID="a" ID="a"e-mail: ppiquini@smail.ufsm.br     

Silicon carbide nanocones: Computational analysis of chemical shieldings for pristine and boron/nitrogen decorated models

Density functional theory (DFT) calculations were performed to investigate the electronic and structural properties of pristine and boron/nitrogen (B/N) decorated models of a representative silicon carbide nanocone (SiCNC). The atoms of apexes and tips were differently decorated by B/N atoms to make all possible decorations of the investigated SiCNC. The evaluated parameters by the optimization processes and nuclear magnetic resonance (NMR) calculations indicated that the overall and atomic scale properties of the investigated SiCNCs are significantly dependent on the ways of decorations of Si/C atoms by B/N atoms. The Si/C atoms close to the decorated regions also exhibited notable changes in comparison to the pristine model.     

外来原子替代碳的氟化石墨烯的磁性和电子性质

采用基于自旋极化密度泛函理论的第一性原理计算,研究了在氟化石墨烯中少量C原子被M原子(M=B,N,Si,P)替代后原子片的磁性和电子性质.结果表明:不同原子掺杂后的氟化石墨烯的电子结构会发生很大的变化,并有很大的不同.掺杂B和P原子后,纳米原子片由半导体转变为金属,并且由非磁性转变为磁性;掺杂N原子后,材料则仍为半导体,但具有磁性;进一步讨论了掺杂原子浓度与磁性的关系.对于Si原子掺杂的氟化石墨烯原子片,其半导体性质不变,但禁带宽度也会发生改变.     

聚铜络合物[Cu(L)μ-1,3-N3]n(ClO4)n的密度泛函计算及磁性研究

基于广义梯度近似密度泛函和全势能线性缀加平面波方法,本文对聚铜络合物[Cu(L)μ-1,3-N3]n(ClO4)n(其中L=tridentate Schiff base为三齿席夫基)的态密度和磁矩进行了计算.磁矩计算结果表明:①该聚铜络合物晶体格子的总磁矩为1.00 μB;②中心铜原子(离子)具有最大的原子磁矩,为0.531 μB;③铜原子和它周围最邻近的氮原子的原子磁矩是该聚铜络合物晶体格子总磁矩的主要来源.通过对中心铜原子及其最邻近氮原子的自旋态密度图进行分析,得出了铜原子和它周围最邻近氮原子的磁性主要分别来源于它们的d轨道和p轨道,同时还发现了中心铜离子的d轨道与叠氮末端氮原子的p轨道之间存在杂化现象, 以及中心铜离子向叠氮末端氮原子的自旋退局域化现象.自旋退局域化效应通过叠氮这一旁道使相邻两中心铜离子发生铁磁性相互作用.     

Stability of (3)He(2)(4)He(n) and (3)He(3)(4)He(n) L=0 clusters

We have studied the stability of mixed (3)He/(4)He clusters in L=0 states by the diffusion Monte Carlo method, employing the Tang-Toennies-Yiu He-He potential. The clusters (3)He(4)He(N) and (3)He(2)(4)He(N) are stable for N>1. The lighter atoms tend to move to the surface of the cluster. The minimum number of 4He atoms able to bind three 3He atoms in a L=0 state is nine. Two of three fermionic helium atoms stay on the surface, while the third one penetrates into the cluster.     

元素替代对LiNH2储氢材料释氢能力影响的第一性原理研究

采用第一性原理赝势平面波方法,研究了元素替代对 LiNH₂释氢能力影响及作用机理.计算给出了结合能、电子态密度、电荷布居,分析了结构的稳定性和原子间的成键情况.结果表明：金属Ca,Na,Al替代LiNH₂部分Li时,可以使N—H键有所减弱.Mg,Al同时替代Li时,效果最好.在Li（Mg）NH₂中,非金属元素B,C,P替代N时,C的效果最好.预测Mg,Al,C共同替代时,会得到的一种较低释氢温度的储氢材料. 关键词： 2储氢材料')" href="#">LiNH₂储氢材料 密度泛函理论 元素替代行为 释氢能力     

Structural stability of heat-treated CoN/CN soft X-ray multilayers fabricated by dual-facing-target sputtering

286 , 176 (1996)]. (1) The interdiffusion critical wavelengths were calculated as 2.00–2.04 nm at temperatures ranging from 473 to 523 K, which is equal to those of Co/C multilayers within the experimental error, indicating that the interdiffusion behaviours in the CoN/CN multilayers are still decided by the thermodynamic properties of the Co-C system. (2) The effective interdiffusivities and macroscopic diffusion coefficients are smaller. (3) The activation energy for diffusion is larger. The features imply that it is possible to improve the thermal stability of Co/C multilayers by doping with N atoms. The high-temperature annealing results imply that the destructive threshold of the CoN/CN multilayers is 100–200 °C higher than that of Co/C multilayers. The small-angle X-ray diffraction of CoN/CN soft X-ray multilayers indicates that the period expansion of the multilayers is only 4% at 400 °C, and the interface pattern still exists even if they were annealed at 700 °C. The large-angle X-ray diffraction and transmission electron microscopy analysis reveal that the crystalline process is significantly retarded if doped with N atoms, leading to a smaller grain size at higher annealing temperatures. The significant improvement of the thermal stability can be interpreted with Raman spectroscopy and X-ray photoelectron spectroscopy analysis. The Raman spectra give the evidence that the formation of the sp³ bonding in the CN sublayers can be suppressed effectively by doping with N atoms, and thus the period expansion resulting from the changes in the density of CN layers can be decreased considerably. The X-ray photoelectron spectra give information about existence of the strong covalent bonding between N atoms and the ionic bonding between Co and N atoms, which can slow down the tendency of the structural relaxation. The interstitial N atoms decrease the mobility of Co atoms, and thus the fcc Co and hcp Co coexist even though the annealing temperature is much higher than the phase transformation temperature of 420 °C, leading to the suppression of the grain growth. Received: 29 May 1997/Accepted: 8 September 1997     

Electronic structure and magnetic properties of the N monodoping and (Li, N)-codoped ZnO

Using first-principles calculations based on density functional theory, we investigated systematically the electronic structures and magnetic properties of N monodoping and (Li, N) codoping in ZnO. The results indicate that monodoping of N in ZnO favors a spin-polarized state with a magnetic moment of 0.95 μ_B per supercell and the magnetic moment mainly comes from the unpaired 2p electrons of N and O atoms. In addition, it was found that monodoping of N in ZnO is a weak ferromagnet and it is the spin-polarized O atoms that mediate the ferromagnetic exchange interaction between the two N atoms. Interestingly, by Li substitutional doping at the cation site (Li_Zn), the ferromagnetic stability can be increased significantly and the formation energy can be evidently reduced for the defective system. Therefore, we think that the enhancement of ferromagnetic stability should be attributed to the accessorial holes and the lower formation energy induced by Li_Zn doping.