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1.
采用半经验的Gupta多体势结合遗传算法对Rhn、Con(n=3~56)团簇的基态结构特性进行了系统的研究.除在n=18~40尺寸范围内有少数团簇的构型不同,两种团簇具有相似的几何结构.在Rhn、Con(n=3~56)团簇的生长中,存在类Ih构型与类fcc构型之间的竞争,对于n≤24,两种团簇都从紧致密堆积结构过渡为类二十面体构型,Rh38及Co38为具有Oh对称性的类fcc构型,从n=39开始,铑团簇和钴团簇都呈现出明显的Ih生长模式.两种团簇的平均束缚能随原子数目的增加而增大,且在所研究的尺寸范围内铑团簇的平均结合能高于钴团簇.Rhn、Con(n=3~56)团簇具有相同的幻数序列:n=13,19,23,38,55.  相似文献   

2.
运用密度泛函方法在(U)B3LYP/LanL2DZ水平上研究了Nb2Sin-(n=1~6)团簇的几何结构和电子性质.结果发现Nb2Sin-(n=1~6)团簇只是在相应的Nb2Sin团簇的结构基础上发生了微小畸变.其中Nb2Si-6团簇结构变化较为严重.对平均束缚能和分裂能的研究发现,Nb2Sin-(n=1~6)团簇的平均束缚能和分裂能均明显高于相应的Nb2Sin团簇,表明增加一个电子可以提高Nb2Sin(n=1~6)团簇的稳定性.通过对最低能构型的分裂能的研究发现,Nb2Si-3团簇和Nb2Si3团簇分别是Nb2Sin-和Nb2Sin(n=1~6)团簇中所有最低能构型中最稳定的.对电荷自然布局的研究发现,在Nb2Sin-(n=1~6)团簇中出现了电子反转.而对于Nb2Sin(n=1~6)团簇,当n=4~6时出现电子反转现象,n=1~2时电子转移符合常规.对HOMO-LUMO能隙的研究结果表明,除了n=1,6外,其余Nb2Sin-(n=2~5)团簇最低能结构的HOMO-LUMO能隙均小于相应的Nb2Sin团簇,说明在这些团簇中增加一个电子增强了团簇的化学活性,但是当n=1、6时增加一个电子,该团簇的化学活性反而降低了.对于Nb2Sin-(n=1~6)团簇来讲,Nb2Si-2和Nb2Si-5团簇分别成为Nb2Sin-(n=1~6)团簇中化学稳定性最强和化学活性最强的.且Nb2Sin-(n=1~6)团簇呈现半导体属性.对磁矩的研究结果表明,Nb2Sin-(n=1~6)团簇的最低能结构的总磁矩均为1.00μB,两个Nb原子的局域磁矩方向,除了Nb2Si5-团簇有一个铌原子与总磁矩相反外,其余均与总磁矩方向相同.说明各团簇中两个铌原子和硅原子对磁矩的贡献不同,方向也不完全相同.  相似文献   

3.
运用密度泛函方法在(U)B3LYP/Lan L2DZ水平上对Nb_2Ge_n(n=1~4)团簇进行了系统的理论研究,得到Nb_2Ge_n(n=1~4)团簇的最低能结构的几何构型和电子性质.优化结果表明:Nb_2Ge_n(n=1~4)团簇最低能结构的自旋多重度均为单重态.团簇最低能结构的电子态与团簇的大小有关.当n为奇数时,团簇的电子态为~1A~1,n为偶数时电子态为1A.通过对计算平均束缚能和分裂能发现:Nb_2Ge_n(n=1~4)团簇中热力学稳定性最强的是Nb_2Ge_2团簇;最弱的是Nb_2Ge_4团簇.自然电荷分布的结果说明Nb_2Ge_n(n=1~4)团簇中当n=1-2时,电子转移正常,而当n=3-4时出现电荷反转现象.同时还研究了HOMOLUMO能隙、磁性和红外光谱.  相似文献   

4.
本文从第一性原理出发,利用密度泛函理论的B3PW91方法,在6-311G水平上对Mg-n,AlMgn-1(n=2~13)团簇进行了几何结构优化和频率分析,并对团簇的平均结合能,二阶能量差分,劈裂能等进行了计算.结果表明:与Mgn团簇相比,带负电Mg-n团簇的最低能量结构整体(除n=6,8,11)变化不大.Al原子的掺杂对Mgn(n=2~13)团簇的最低能量结构没有太大影响,Mgn,AlMgn-1团簇有类似的结构生长方式.带一个负电和掺杂一个Al原子均能使Mgn团簇的平均结合能增大,稳定性增强.并发现Mg-n(n=2~13)团簇在n=4,9时比较稳定,在n=11时稳定性较差,与实验结果一致;而等电子的AlMgn-1团簇在n=4,7,9时比较稳定.  相似文献   

5.
运用杂化密度泛函理论方法在(U)B3LYP/Lan L2DZ水平研究了Ru Sin(n=1~6)团簇体系的稳定结构及电子性质.结果发现:Ru Sin(n=1~6)团簇基本保持了纯硅团簇的框架.对原子平均束缚能和分裂能的计算表明,Ru Si6团簇是Ru Sin(n=1~6)团簇中热力学稳定性最强的.对自然电荷分布的研究结果发现,Ru Sin(n=2,4~6)团簇的最低能结构出现电荷反转现象.HOMO-LUMO能隙的研究结果表明掺入钌原子后团簇的化学活性增强了,且Ru Si的化学活性是Ru Sin(n=1~6)团簇最强的.通过对团簇磁矩的研究发现,Ru Si和Ru Si3团簇具有了磁性,其余团簇的总磁矩为零,且Ru Sin(n=1~6)团簇中各原子对团簇总磁矩的贡献不同.  相似文献   

6.
运用杂化密度泛函理论方法在(U)B3LYP/LanL2DZ水平研究了RuSin(n=1~6)团簇体系的稳定结构及电子性质.结果发现:RuSin(n=1~6)团簇基本保持了纯硅团簇的框架.对原子平均束缚能和分裂能的计算表明,RuSi6团簇是RuSin(n=1~6)团簇中热力学稳定性最强的.对自然电荷分布的研究结果发现,RuSin(n=2,4~6)团簇的最低能结构出现电荷反转现象. HOMO-LUMO能隙的研究结果表明掺入钌原子后团簇的化学活性增强了,且RuSi的化学活性是RuSin(n=1~6)团簇最强的。通过对团簇磁矩的研究发现,RuSi和RuSi3团簇具有了磁性,其余团簇的总磁矩为零,且RuSin(n=1~6)团簇中各原子对团簇总磁矩的贡献不同.  相似文献   

7.
采用密度泛函理论中的PW91/DNP方法研究了Cun(n=2~20)团簇的稳定性和电子性质.结果表明:在n=2~8区间,平均结合能曲线几乎呈现线性增长;在n=9~20区间,平均结合能曲线相对较平缓.Cun(n=4,7,8,17)团簇相对较稳定.Cun(n=2,4,8,13,19)团簇的能隙值相对较大,化学活性较弱.在n=2~20区间,垂直电离能略微大于绝热电离能,绝热亲和能略微大于垂直亲和能.在n=2~9区间,电离能曲线呈现出显著的奇—偶振荡效应,即n为偶数团簇的电离能比临近奇数团簇的要大;亲和能曲线呈现出同电离能曲线相反的奇—偶振荡效应.  相似文献   

8.
利用密度泛函理论的B3LYP/LanL2DZ方法,对AgGe_n(n=1~17)团簇进行了系统的研究,较小的AgGe_m(n=1~11)和相对较大的AgGe_n(n=12~17)团簇出现了不同的生长方式.从n=12开始,形成了银原子被锗原子完全包围的笼状结构.根据AgGe_n团簇的分裂能和二阶能量差分,预测了AgGe_n(n=1~17)团簇的幻数为n=5、10、12和15.Mulliken电荷布局分析显示电荷转移的方向和团簇的大小与掺杂的金属种类有关.通过分析振动光谱,研究了团簇的动态稳定性,在实验中明显的红外谱和拉曼谱能被用来区别团簇结构.  相似文献   

9.
从头计算对GanNm团簇的结构与稳定性的研究   总被引:2,自引:0,他引:2  
用B3LYP-DFT方法对GanN2(n=1~7)和GanN(n=2~8)团簇的结构与稳定性进行了研究.在6-31G*水平上进行了结构优化和频率分析,得到了GanN2(n=1~7)和GanN(n=2~8)团簇的基态结构.在GanN(n=2~8)团簇的基态几何结构中,N原子处在分子结构的中心;在GanN2(n=1~3)团簇中,N—N键比Ga—N键强;在GanN2(n=4~7)团簇中存在Ga3N单元和Ga4N单元.在GanN2(n=1~7)和GanN(n=2~8)团簇中,Ga4N2,Ga6P2,Ga3N,Ga5N和Ga7N较其它团簇稳定.  相似文献   

10.
采用密度泛函理论下广义梯度近似方法,对Mn掺杂Ge基半导体团簇Ge_nMn(n≤8)的结构与磁性进行了理论研究.结果表明:Ge_nMn(n≤8)的最稳定构型与相应的Ge_(n+1)团簇相似.Mn掺杂后团簇的原子平均结合能与纯锗团簇比较近似;能量二次差分表明:Ge_3Mn和Ge_5Mn团簇较相邻团簇表现出较高的稳定性;当n=1,3和6时,HMO-LUMO能隙较大,n=2时,能隙较小,说明GeMn、Ge_3Mn和Ge_6Mn具有相对较好的化学稳定性,而Ge_2Mn具有较高的化学活性.对Ge_nMn(n≤8)团簇的磁性研究发现,除Ge_8Mn的总磁矩为1μB外,其他团簇的总磁矩均为3μB,且团簇的磁性主要来源于Mn原子.  相似文献   

11.
Two-dimensional scanning of a 0.6328 mum guided-light beam has been realized using noncolinear acousto-optic (AO) coplanar Bragg diffraction together with colinear AO guided-mode to substrate radiation-mode conversion in a Z-cut Xpropagation LiNbO3 proton-exchanged (PE) waveguide. The two surface acoustic (SAW) waves utilized are at the center frequencies of 500 and 200 MHz, propagating in the Y and X axes, respectively. Two-dimensional scanning of approximately 720 resolvable light beam spots, namely, 18 40 (horizontal vertical) scanning, has been demonstrated using a light beam of 1.0 mm aperture. The total number of resolvable beam spots can be greatly increased from 720 by simply utilizing SAW transducers of larger bandwidth and a light beam of greater aperture. It should also be possible to significantly increase the diffraction efficiency from 3 % by optimizing the parameters of the PE waveguide and the SAWs.  相似文献   

12.
A simple technique of pulse compression, based on the linear chirp compensation of self-phase modulation (SPM) spectra in dispersion shifted fibers, is demonstrated. The optimization procedure is carried out, for a short span of a single-mode fiber, using a parabolic law, which describes the behavior of the squared output pulse width versus the pump peak power in the case of Gaussian pulses. The experimental results give a minimum pulse duration of 233 fs, which is in good agreement with the model. Shorter and coherent pulses, down to 90 fs, have been obtained by inserting an interference filter at the optical output.  相似文献   

13.
A review of schemes for multiple access in fiber optic networks shows that a hybrid of wavelength and code division multiple access (WCDMA) combines the best features of both. In particular, the hybrid scheme retains the large information carrying capacity of wavelength division multiple access (WDMA) and flexibility of code division multiple access (CDMA). In this paper WDMA, optical CDMA (OCDMA), and WCDMA networks are discussed. In OCDMA networks, concept of incoherent and coherent coding including inverse decoding and matched filter is introduced. The delay performance of both WDMA and WCDMA networks, under the simple suboptimum access protocols based on cyclic search, is computed. It has been shown quantitatively that tuning delay significantly affects the delay performance of both WDMA and WCDMA networks. Futhermore, delay performance of WCDMA networks is always better than the WDMA networks for the same tuning delay, load, and number of users.  相似文献   

14.
The Shanghai Synchrotron Radiation Facility(SSRF)booster ring,a full energy injector for the storage ring,is deigned to accelerate the electron beam energy from 150MeV to 3.5GeV that demands high extraction efficiency at the extraction energy with low beam loss rate when electrons are ramping.Closed orbit distortion(COD)caused by bending magnet field uniformity errors which affects the machine performance harmfully could be effectively reduced by bending magnet location sorting.Considering the affections of random errors in measurement,both ideal sorting and realistic sorting are studied based on measured bending magnet field uniformity errors and one reasonable combination of bending magnets which can reduce the horizontal COD by a factor of 5is given as the final installation sequence of the booster bending magnets in this paper.  相似文献   

15.
16.
Results of a study of the effect of γ-radiation on the spectral luminescence properties of cadmium tungstate crystals doped with silver, bismuth, and molybdenum cations are presented. Spectral characteristics of the nondnnnoped crystals are briefly described. Absorption and photo and X-ray luminescence spectra of the crystals taken before and after exposure to γ-radiation (5.5·104 Gy) are compared. It is found that the spectral characteristics of the crystals doped with silver, bismuth, and molybdenum cations do not change markedly after the exposure. The relation between the type of impurity-induced defects, individual characteristics of the impurity cations, and the character of the effect of γ-radiation on the spectral luminescence properties of impure crystals is analyzed (preliminarily). Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 1, pp. 55–60, January–February, 1997.  相似文献   

17.
A transient suppression method for piezoelectric ceramic transducer is presented. By adding some special pedestal pulses to the original transmitted signal, the transient effects in the output of the transducer can be just precisely transmission by use of a narrowband transducer. canceled, thereby achieving the broadband The experimental results show that the transient responses of the sinusoid pulses and coded signals are suppressed successfully and the acoustic waveforms radiated into the surrounding water are improved significantly.  相似文献   

18.
We experimentally demonstrate amplitude squeezed soliton utilizing intensity-dependent self-phase modulation in an asymmetric Sagnac interferometer.The system.whose components are connected via ferrule connector/physical connection(FC/PC)fiber connectors,constitutes all-fiber configuration to generate squeezed soliton.Soliton amplitude reduction measured by homodyne detection is near 4.0 dB below the shot-noise level.Optimal squeezing fields in both simple and compact all-fiber configuration are obtained.  相似文献   

19.
The(2 1)-dimensional nonlinear Schr(o)dinger(NLS)equation with spatially inhomogeneous nonlinearities is investigated,which describes propagation of light in(2 1)-dimensional nonlinear optical media with inhomogeneous nonlinearities.New types of optical modes and nonlinear effects in optical media are presented numerically.The results reveal that the regular split of beam can be obtained in (2 1)-dimensional nonlinear optical media with inhomogeneous nonlinearities,by adjusting the guiding parameter.Furthermore,the stability of beam regular split is discussed numerically,and the results reveal that the beam regular split is stable to the finite initial perturbations.  相似文献   

20.
In the real-world application of face recognition system, owing to the difficulties of collecting samples or storage space of systems, only one sample image per person is stored in the system, which is so-called one sample per person problem. Moreover, pose and illumination have impact on recognition performance. We propose a novel pose and illumination robust algorithm for face recognition with a single training image per person to solve the above limitations. Experimental results show that the proposed algorithm is an efficient and practical approach for face recognition.  相似文献   

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