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1.
用密度泛函理论(DFT)的B3LYP/6-311G*方法,对Si2CmN(m=2-10)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=2-10的团簇为线性结构,随着m的增大,团簇的自旋多重度均为2,Si原子在C与N原子形成的线性链端部成键,团簇的基态能量近似线性增大。m为偶数的Si2CmN团簇比m为奇数的更为稳定。  相似文献   

2.
GanNm+(n=1~8,m=1~2)团簇的结构及稳定性的DFT研究   总被引:2,自引:2,他引:2  
用密度泛函理论(DFT)的B3LYP方法在6-31C*水平上对GanN (n=2~8)和GanN2 (n=1~7)阳离子团簇的几何结构、稳定性和振动频率等进行研究,得到GanN (n=2~8)和GanN2 (n=1~7)阳离子团簇的基态结构.其中,GanN (n=2~8)团簇在总原子数≤6时,其几何结构为平面结构,总原子数>6时,其几何结构为立体结构,N原子位于立体结构的中心;GanN2 (n=2~7)团簇在总原子数≤7时,其基态几何结构为平面结构,总原子数>7时,其基态几何结构为立体结构;原子总数为奇数的团簇Ga4N ,Ga6N ,Ga3N2 和Ga5N2 的基态结构较稳定.  相似文献   

3.
从第一性原理出发利用密度泛函理论(DFT)计算了LiNBe(N=1-12)团簇的基态结构及其电子性质.计算结果表明:铍掺杂锂团簇LiNBe(N=1-12)的基态结构相当于Be原子取代LiN 1主团簇基态结构中一个Li原子的位置;当团簇尺寸N≥6时,杂质原子Be被束缚在主团簇笼子内;随着团簇尺寸增大,团簇的离解能和二阶能量差分均出现了奇-偶振荡;从结构稳定性上来看,Li6Be是个幻数团簇.  相似文献   

4.
采用第一性原理在B3LYP\6-311G水平上对MnPm(n=1~2, m=1~10)(M=Be 、Mg 、Ca)团簇进行几何构型优化和频率分析,得到团簇各个尺寸的基态结构,结果表明,在m+n=5~6时锥体结构居多,相应的稳定性要高于同尺寸其他构型,m+n>6时,基态结构中出现四元环和五元环。裂化能和二阶能量差分计算结果表明,MPm(m=1~10)团簇在m=2时同时获得局域的最大值, Be2Pm(m=1~10)团簇幻数结构呈现规则的奇偶振荡。Be掺杂P团簇稳定性高于同尺寸的Mg 、Ca掺杂,与Mg 、Ca相比Be原子更易于与P原子结合。稳定结构团簇红外和拉曼光谱显示,高频段MP2团簇红外和拉曼活性较强,Mg2P2, Ca2P2团簇红外谱主峰在高频段出现,与拉曼活性谱主峰相反。  相似文献   

5.
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   

6.
采用密度泛函(DFT)中的B3LYP方法,选择CEP-31g基组,优化并得到了MgnLa(n=2- 6)小团簇的基态平衡结构,计算出了掺杂团簇的基态结构的平均键长、对称性、费米能级、能级间隙、束缚能、总能的二阶差分.结果表明,随着团簇原子数的增加,La原子更容易趋于团簇表面位置. 与未掺杂Mg团簇相比,La原子多采用取代其稳定基态结构的一个Mg原子形成掺杂团簇的稳定结构. 从有限的结果看,其中 Mg3La和 Mg6La的结构更为稳定.  相似文献   

7.
CoAlN(N=2-11)团簇基态结构的稳定性和磁性   总被引:1,自引:1,他引:0  
采用密度泛函理论中的广义梯度近似(GGA),对CoAlN(N=2-11)团簇进行构型优化和磁性计算.在考虑自旋多重度的情况下得到了团簇的平衡构型及基态结构,并重点讨论了Co原子的sp-d杂化效应对体系稳定性和磁性的影响.结果表明:N为偶数时,团簇的基态为自旋双重态,Co原子磁矩随N增加整体上呈减小趋势;N为奇数时(除N=5为自旋三重态外),团簇的基态为自旋单重态,Co原子磁矩为零.N≥8时,Co原子陷入主团簇内部,体系的对称性降低,稳定性增强;轨道杂化增强了体系的稳定性,但减小了双重态和三重态体系中Co原子的磁矩;N=3,8,10是团簇CoAlN(N=2.11)的幻数.  相似文献   

8.
GanN-m阴离子团簇的结构及稳定性的研究   总被引:2,自引:0,他引:2       下载免费PDF全文
利用密度泛函理论(DFT)对GanN-(n=2-8)和GanN2-(n=1-7)阴离子团簇的结构及稳定性进行了研究.在B3LYP/6-31G*水平上进行了结构优化和频率分析,得到了GanN-(n=2-8)和GanN2-(n=1-7)阴离子团簇的基态结构.在这些团簇中,原子总数小于等于6的团簇的几何结构为平面结构,原子总数大于6的团簇的几何结构为立体结构;在所研究的团簇中,Ga4N-,Ga6N-,Ga4N-2和Ga5N-2的基态结构较稳定.  相似文献   

9.
陈玉红  张材荣  马军 《物理学报》2006,55(1):171-178
用密度泛函理论(DFT)的杂化密度泛函B3LYP方法在6-31G基组水平上对MgmBn(m=1,2;n=1-4)团簇各种可能的构型进行几何结构优化,预测了各团簇的最稳定结构.并对最稳定结构的振动特性、电离势、成键特性、极化率和超极化率等性质进行了理论研究.结果表明,团簇的最稳定结构大多是平面结构,团簇的稳定结构中通常是几个呈负电性的B原子形成一个负电中心,而其他B原子和Mg原子通常处在端位,且显正电性;团簇中通常是B-B键和B-Mg键共存,极少出现Mg-Mg键, 关键词: mBn(m=1')" href="#">MgmBn(m=1 n=1-4)团簇 密度泛函理论 结构与性质  相似文献   

10.
用密度泛函理论(DFT)的B3LYP/6-311G*方法,对SiCmN(m=1-7)团簇的几何构型、振动频率和基态能量等性质进行了研究,讨论了化学键的特征和热力学稳定性。振动频率和振动强度被用来判断体系的基态结构。结果表明,m=1~5的团簇为线状结构,m=6、7的团簇为环状结构。m增大过程中,线状团簇自旋多重度均为2,而环状团簇出现2、4和6自旋多重度。能量的二次差分值表明m为奇数的团簇比m为偶数的更为稳定。  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.
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   

14.
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   

15.
16.
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   

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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