Si2CmN团簇的结构及稳定性的密度泛函理论研究

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。     

GanNm+(n=1～8,m=1～2)团簇的结构及稳定性的DFT研究

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.     

第一性原理计算LiNBe(N=1～12)团簇的基态结构及其电子性质

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.     

从头计算对GanNm团簇的结构与稳定性的研究

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.     

碱土金属Be 、Mg 、Ca掺杂磷团簇结构演变规律与光谱性质研究

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。     

CoAlN(N=2-11)团簇基态结构的稳定性和磁性

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.     

GanN-m阴离子团簇的结构及稳定性的研究

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.     

MgnLa(n=2-6)掺杂团簇的密度泛函研究

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．     

密度泛函理论研究Bn Ni(n=6-12)团簇的结构和磁性

基于第一性原理,用密度泛函理论中的广义梯度近似(generalized gradient approximation,GGA)方法,在充分考虑自旋多重度的前提下,优化并得到了Bn(n=6一12)和BnNi(n=6-12)团簇的平衡构型,按照能量最低原理确定其基态结构.Bn团簇的计算结果与已有的理论结果相一致.当Ni原子掺杂在Bn团簇中,B12Ni团簇的基态结构为平面结构,其余均为三维结构.基态结构的自旋多重度除了n=8以外呈现2,l交替的规律.计算团簇基态结构的平均结合能(Eb)、团簇能量的二阶差分(△2 E)和能隙(HOMO.I.UMO,gap)均表明,l=8为B.Ni(,l=6一12)团簇的幻数,即B8Ni团簇较相邻团簇稳定.计算团簇的磁矩表明B8Ni团簇磁矩最大(2цB),团簇总磁矩和平均磁矩随团簇尺寸增大呈现奇偶振荡趋势且磁矩主要由Ni原子的3d轨道提供.     

第一性原理研究SinB(n=1～12)团簇的稳定性

基于密度泛函理论(DFT),我们研究了SinB(n=1～12)团簇的稳定性.结果表明:SinB的基态构型是在Sin-1B的基态或亚稳态构型上带帽一个Si原子而得到;随着团簇尺寸的增大,B原子逐渐从吸附在Sin团簇的表面位置移动到Sin团簇笼内;掺杂B原子提高了纯硅团簇的稳定性;电子总是从Si向B转移,B原子所带的电荷数不仅与B原子的配位数有关,还与SinB团簇的基态结构密切相关.     

Theoretical analysis and simulation of conjugate heights for dual-conjugate AO system in lidar

A multi-conjugate adaptive optics （MCAO） can offer a possibility of widening field of view （FOV） characterized by the isoplanatic angle, and the choose of conjugate height becomes a basic problem for MCAO, which influences the size of iosplanatic angle. Considering the application of lidar, the isoplanatic angle＇s expressions of two deformable mirrors （DMs） MCAO for uplink and downlink are deduced. The effects of conjugate heights for dual-conjugate AO are thoughtfully discussed, and the isoplanatic angles are further analyzed. The results show that the isopanatic angle varies with the conjugate height and reaches the maximum as the conjugate height is at the optimal altitude. Moreover, the optimal conjugate height changes with the propagation distance.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Characterization of PolyA and PolyC mismatches by Raman spectroscopy

A.C mismatches are studied by Raman spectral characterization of PolyA, PolyC, and their equimolar complex in solution of 0.14 mol/L Na ,pH7.0.Experimental results show that A·C mismatches occur to be A/B (mainly A) conformers, and unlike Watson-Crick base pairing, this kind of mismatches is stabilized by only one hydrogen bond involving cytosine N4H2 and adenine N7.The formation of A·C complex makes the base stacking interactions much stronger, and conformation of the backbone more ordered, which leads to obvious Raman hypochromic effect with some shifts in corresponding bands.     

Improvement of four-wave mixing-based wavelength conversion efficiency in dispersion shifted fiber by 40-GHz clock pumping

40-GHz clock modulated signal as a pump to improve the efficiency of four-wave mixing (FWM)-based wavelength conversion in a 26.5-km dispersion shifted fiber (DSF) is investigated. The experimental results demonstrate that the conjugated FWM component has higher intensity with the clock pumping than that with the continuous-wave (CW) light pumping. The improvement of FWM-based wavelength conversion efficiency is negligible when the pump power is less than Brillouin threshold. But when the pump power is greater than Brillouin threshold, the improvement becomes significant and increases with the increment of pump power. The improvement can increase up to 9 dB if pump power reaches 17 dBm.     

Multi-pulse operation of a Kerr-lens mode-locked femtosecond laser

Our experimental results show that the presence of a proper amount of negative group velocity dispersion is essential to multi-pulse operation of a Kerr-lens mode-locked femtosecond laser. We demonstrate that the pulse separations and the number of pulses contained within a cavity round trip are strongly dependent on the initial perturbations. The results allow us to get a better understanding on the influences of the convoluted self-phase modulation and intra-cavity dispersions on the stable multi-pulse oscillation in a Kerr-lens mode-locked femtosecond laser.     

Propagation of Helmholtz-Gauss beams in weak turbulent atmosphere

Based on the Rytov approximation of light propagation in weak turbulent atmosphere,the closed-form expressions of field and average irradiance of each one of the four fundamental families of Helmholtz-Gauss (HzG)beams:cosine-Gauss beams,stationary Mathieu-Gauss beams,stationary parabolic-Gauss beams,and Bessel-Gauss beams,which are propagating in weak turbulent atmosphere,are obtained.The results show that the field and average irradiance can be written as the product of four factors:complex amplitude depending on the z-coordinate only,a Ganssian beam.a factor of complex phase perturbation induced by atmospheric turbulence,and a complex scaled version of the transverse shape of the non-diffracting beam.The effect of weak atmospheric turbulence on irradiance distribution of the HzG beam can be ignored.     

An effective method for reducing speckle noise in digital holography

An effective method for reducing the speckle noise in digital holography is proposed in this paper.Different from the methods based on classical filtering technique,it utilizes the multiple holograms which are generated by rotating the illuminating light continuously.The intensity images reconstructed by a series of holograms generated by rotating the illuminating light possess different speckle patterns.Hence by properly averaging the reconstructed intensity fields,the speckle noises can be reduced greatly.Experimental results show that the proposed method is simple and effective to reduce speckle noise in digital holography.     

Influence of purity of HfO2 on reflectance of ultraviolet multilayer

The impurities in two kinds of HfO2 materials and in their corresponding single layer thin films were determined through glow discharge mass spectrum technology and secondary ion mass spectrometry(SIMS) equipment respectively.It was found that ZrO2 was the main impurity in the two kinds of HfO2 either in the original HfO2 materials or in the electron beam deposited films.In addition,the difference of Zr content in the two kinds of HfO2 single laver films was much laxger than that of the other impurities such as Ti and Fe.which showed that it was just ZrO2 that made the difference between the optical performance of the film products including the two kinds of HfO2.With these two kinds of HfO2 and the same kind of SiO2.we deposited HfO2/SiO2 multilayer reflective coatings at the wavelength of 266 nm.Experimental results showed that the reflectances of these two mirrors were about 99.85% and 99.15% respectively,which agreed well with the designed results what were based on the optical constants obtained from the corresponding single layer thin films.     

Speech enhancement by array crosstalk resistant ANC and spectrum subtraction

Microphone array-based speech enhancement has great importance for speech communications and speech recognition. To reduce the aperture of the microphone array and to increase the effect of the speech enhancement will greatly broaden the application areas of the microphone array. An array crosstalk resistant adaptive noise cancellation method is therefore presented. And then an improved spectral subtraction algorithm is further cascaded to obtain better enhancement results. Theoretic analysis and experiments indicate that the proposed scheme needs only a very small microphone array while it simultaneously achieves a higher SNR improvement. Besides, the proposed scheme can be used in many noisy environments and is easy for real-time implementation.