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.     

CoBn(n≤19)团簇结构、电子性质和磁性的密度泛函理论研究

采用密度泛函理论中的广义梯度近似(Generalized Gradient Approximation, GGA)方法, 对不同自旋多重度的CoBn(n≤19)团簇的平衡几何结构、电子性质和磁性进行了研究. 随着尺寸的增加, CoBn(n≤19)团簇最低能量结构从平面结构逐步演变为立体结构, Co从主团簇的外部向内部转移. 团簇最低能量结构的二阶能量差分表明CoB3、CoB7、CoB10、CoB12、CoB14和CoB16团簇较相邻团簇稳定. Co的掺杂增强了硼团簇的化学活性. 最低能量结构中Co的d轨道和B的p轨道存在着明显的杂化. 当n<13, Co处于主团簇的外部时, Co的带电量为正, Co具有磁矩. 当n≥13, Co处于主团簇的内部时, Co的带电量为负, Co的磁矩几乎为零. 团簇最低能量结构的总磁矩主要来自Co的3d轨道的贡献, 且总磁矩随团簇尺寸增大呈现奇偶振荡.     

YnN(n=2-12)团簇的结构与性质研究

在密度泛函理论框架下,用广义梯度近似（GGA）的方法研究YnN（n=2-12）团簇的电子结构,系统计算了它们的基态束缚能Be（eV）、最高占据轨道（HOMO）与最低未占据轨道（LUMO）之间的能隙、二阶能量差分 (au)、离解能 (au)、团簇的总磁矩Mt（ ）,最近邻N原子的Y原子所带的局域电荷QY（C）和磁矩MY（ ）、掺杂原子N所带的局域电荷QN（C）和磁矩MN（ ）。研究表明,Y6N、Y8N、Y10N的基态具有较高稳定性;对于YnN（n=2-12）的所有团簇,电荷总是由Y原子转移到N原子,YnN（n=2-12）团簇中Y—N表现为离子键的性质;当n=3,4,5,9,10,11,12时,团簇的磁矩为零,团簇的磁性消失,当n=2,6,7,8时,团簇具有磁性,其中n=6时,团簇的磁性最强。     

Nb_2Si_n~-(n=1～6)团簇的几何构型、电子性质和磁性的理论研究

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.     

密度泛函理论研究SinMn (n=2～14)团簇的结构和电子性质

采用密度泛函理论中的广义梯度近似对SinMn (n=2～14) 团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算. 结果表明,当n≥10时,Mn原子完全陷入Si原子形成的笼内.二阶能量差分、分裂能和垂直电离势都表明Si5Mn和Si12Mn是稳定的团簇,且12是团簇的幻数.通过对电子性质的分析发现Si12Mn团簇具有较高的化学稳定性.布局数分析表明,在Si5Mn团簇中Mn原子的磁矩(3.923 μB)是最大的.较多的电荷转移以及Mn原子的4s, 3d态和Si原子的3s, 4p态的较强杂化是导致Mn原子磁矩减小的原因.当n≥7时,SinMn 的总磁矩是1 μB.     

Ge_nMn(n≤8)团簇的电子结构与磁性的密度泛函理论研究

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.     

Nb2Sin-(n=1-6) 团簇的几何构型、电子性质和磁性的理论研究

运用密度泛函方法在(U)B3LYP/LanL2DZ水平上研究了 (n=1～6)团簇的几何结构和电子性质．结果发现 (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 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, 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, 团簇和Nb2Si3团簇分别是 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 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 (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 (n=1～6)团簇来讲, 和 团簇分别成为 (n=1～6)团簇中化学稳定性最强和化学活性最强的．且 (n=1~6)团簇呈现半导体属性．对磁矩的研究结果表明, (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 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．     

SinMn (n=2--14) 的结构和电子性质

采用密度泛函理论对SinMn (n=2--14)的几何结构和电子性质进行了研究,结果表明,从Si12Mn 团簇开始,Mn原子陷入了Si原子形成的笼内;二阶能量差分,分裂能和垂直电离势都表明5,10,12是团簇的幻数,其中Si12Mn团簇是最稳定的;在所研究的团簇中,Si5Mn团簇中Mn原子的磁矩是最大的(3.923uB);Mn 原子的4s, 3d 和Si原子的3s, 4p的较强杂化是导致Mn原子磁矩减小的原因;当n ≥7时,SinMn团簇的总磁矩是1 uB.     

BnTi(n=1-12)团簇的结构, 电子性质和磁性

利用密度泛函理论广义梯度近似方法得到了BnTi(n=1-12)团簇的基态结构, 并讨论了电子性质和磁性质. 结果表明, n≤5 时, BnTi 基态结构呈平面或准平面, n>5 时, Ti 原子倾向于与较多的B 原子成键而呈三维结构. 由二阶能量差分得出B3Ti, B5Ti, B10Ti 为幻数团簇. Mulliken 布居分析显示BnTi 团簇中电荷由Ti 原子向近邻B 原子转移且以共价键与离子键共存; 除BTi 磁矩为5 μB 外, 其余团簇磁矩处于0-2 μB 之间; 团簇总磁矩主要由Ti 原子的3d 轨道和个别B 原子提供. B3Ti和B7Ti 团簇中, B 原子表现为反铁磁性.     

BnTi(n=1-12)团簇的结构, 电子性质和磁性

利用密度泛函理论广义梯度近似方法得到了BnTi(n=1-12)团簇的基态结构, 并讨论了电子性质和磁性质. 结果表明, n≤5 时, BnTi 基态结构呈平面或准平面, n>5 时, Ti 原子倾向于与较多的B 原子成键而呈三维结构. 由二阶能量差分得出B3Ti, B5Ti, B10Ti 为幻数团簇. Mulliken 布居分析显示BnTi 团簇中电荷由Ti 原子向近邻B 原子转移且以共价键与离子键共存; 除BTi 磁矩为5 μB 外, 其余团簇磁矩处于0-2 μB 之间; 团簇总磁矩主要由Ti 原子的3d 轨道和个别B 原子提供. B3Ti和B7Ti 团簇中, B 原子表现为反铁磁性.     

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.