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1.
MgO是具有强极性的离子化合物,电场诱导MgO吸附H_2是一种有效的储氢方法,但外加的电场很强,如何降低所需电场的强度是需要解决的关键问题.本文在密度泛函理论水平上研究了电场中H_2在(MgO)_4团簇上的吸附性质.结果表明(MgO)_4能承受强电场并保持立方结构,可用于电场储氢.电荷分析表明(MgO)_4在电场中被极化,其偶极矩增大为场强0.005 a.u.和0.010 a.u.时的1.67和3.33 Debye. H_2能稳定吸附在单个Mg/O原子上. H_2在Mg上为侧位吸附,而在O上为端位吸附.外加电场可提高其吸附强度.仅需0.010 a. u.的外电场,就可使H_2在Mg/O上的吸附能由无电场时–0.118/–0.060 eV提高到–0.225/–0.150 eV.所需电场强度小于较大尺寸的(MgO)9团簇,表明降低团簇尺寸是减少所需电场强度的一种可能方式.利用QTAIM方法研究了H_2与(MgO)_4间的弱相互作用,表明电场使团簇及氢分子极化,从而增强了其间的静电作用.当团簇尺寸降低时,更多的原子位于表面,且具有较低的配位数,更容易被极化,因此储氢所需的电场强度更低.电场中(MgO)_4中最多能吸附16个H_2,相应的质量密度为16.7 wt%,表明(MgO)_4是一种可能的电场储氢材料. 相似文献
2.
三角形钠原子团簇中的表面等离激元 总被引:1,自引:0,他引:1
运用含时密度泛函理论研究等边三角形钠原子团簇中的表面等离激元激发.发现:在团簇尺寸较大时,沿三角形底边和底边中垂线方向激发的共振模式不同,然而沿两方向的吸收光谱线形一样,主要吸收峰的共振能量也相同.低能聚集共振在空间引起电场增强的极大值主要分布在三角形的端点附近. 相似文献
3.
利用基于密度泛函理论的第一性原理方法,在广义梯度近似(GGA)下对Ga_(2n)(n=1~4)团簇进行了几何结构优化和结合能计算,并对其电子结构及成键特性进行了分析.结果表明,Ga_2,Ga_4团簇的基态都是自旋极化态,Ga_6团簇的能量局域极小的八面体结构也具有自旋极化;这些团簇的最外层分子轨道的空间分布是对称的,最外层分子轨道之间的能量相差很小,最外层分子轨道的近简并引起了自旋极化;对称性较高的团簇容易形成近简并的最外层分子轨道. 相似文献
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利用过渡金属掺杂的硅基团簇, 构建了一种自旋分子结; 并利用第一性原理方法, 对其电子自旋极化输运性质进行了研究. 计算表明, 通过过渡金属掺杂可以有效地产生自旋极化电流, 磁性金属Fe和非磁性金属Cr和Mn掺杂的体系呈现出较明显的自旋极化透射现象, 但分子结的自旋极化输运能力与团簇孤立状态下的磁矩无一致性.从Sc到Ni的掺杂, 体系的自旋极化透射能力先增大后迅速减小, 在Fe掺杂的Si12团簇中出现最大值.
关键词:
硅团簇
自旋极化输运
密度泛函理论
非平衡格林函数 相似文献
7.
采用密度泛函理论(DFT)中的B3LYP方法,在LANL2DZ基组水平上对WnNim(n+m=8)团簇的各种可能构型进行了几何参数全优化,得到了它们的基态构型;并对基态构型的偶极距、极化率、红外光谱和拉曼光谱性质进行了分析,结果表明:团簇WnNim(n+m=8)都具有极性,富W团簇非线性光学效应强,容易被外加场极化;振动频率主要分布在0-350 cm-1范围内,团簇W4Ni4因其振动方式的特殊性,红外光谱和拉曼光谱在频率421.971 cm-1处,都有明显强峰;团簇W5Ni3因其结构的高对称性在振动光谱中出现多处共振现象. 相似文献
8.
采用密度泛函m062x的方法在6-31g(d)基组上对双酚A型环氧树脂分子进行优化得到了它的稳定结构,并且研究了不同外电场(0-0.013 a.u., 1 a.u.=5.142×10~(11) V/m)作用下双酚A型环氧树脂分子的分子结构、电偶极矩和分子总能量,偶极矩、极化率、前线轨道的能级和成分,原子之间的键能和红外光谱的变化.研究表明:随着外加电场的增大,双酚A型环氧树脂分子从倒V型结构逐渐变成线性结构,总能量降低,偶极矩和极化率都升高,且双酚A型环氧树脂分子的稳定性随着外加电场的增大而降低;最高占据轨道能级随着外加电场的增大而增大,沿逆电场方向分子链端表现出亲核反应活性,最低空轨道能级随着外加电场的增大而减小,沿电场方向分子链端表现出亲电反应;位于分子两端环氧基团上的C-C,C-O容易发生断裂,进而破环了双酚A型环氧树脂分子的稳定性;分子红外光谱在高频区的吸收峰出现了明显的红移现象. 相似文献
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《原子与分子物理学报》2021,(2)
采用密度泛函m062x的方法在6-31g(d)基组上对双酚A型环氧树脂分子进行优化得到了它的稳定结构,并且研究了不同外电场(0-0.013 a.u.,1 a.u.=5.142×10~(11)V/m)作用下双酚A型环氧树脂分子的分子结构、电偶极矩和分子总能量,偶极矩、极化率、前线轨道的能级和成分,原子之间的键能和红外光谱的变化.研究表明:随着外加电场的增大,双酚A型环氧树脂分子从倒V型结构逐渐变成线性结构,总能量降低,偶极矩和极化率都升高,且双酚A型环氧树脂分子的稳定性随着外加电场的增大而降低;最高占据轨道能级随着外加电场的增大而增大,沿逆电场方向分子链端表现出亲核反应活性,最低空轨道能级随着外加电场的增大而减小,沿电场方向分子链端表现出亲电反应;位于分子两端环氧基团上的CC,C-O容易发生断裂,进而破环了双酚A型环氧树脂分子的稳定性;分子红外光谱在高频区的吸收峰出现了明显的红移现象. 相似文献
11.
通过建立石墨烯的光学布洛赫方程, 研究了弱光场下的单层石墨烯超快动态光学性质. 理论研究表明在太赫兹辐射光场下由于泡利不相容和能量守恒原理使得石墨烯系统建立动态非平衡载流子并达到饱和的时间是20–200 fs, 能够在1 ps之内迅速产生光电流. 研究发现√2evF E0 t<0 和ω 分别对应入射光的强度和频率, t为时间, vF是石墨烯狄拉克点附近电子的费米速度. 研究发现光子能量?ω越大, 电极化强度以及光电流越强. 我们的理论研究结果与已有的众多实验结果一致, 表明石墨烯在超快动态光学领域尤其是太赫兹领域拥有重要的研究和应用价值. 相似文献
12.
Abdelilah Mejdoubi 《Physics letters. A》2008,372(6):741-748
Based on the finite-element method, it is demonstrated that the electrostatic resonance features of a range of heterostructures made of clusters of dielectric cylinders depend sensitively on the shape and arrangement of the inclusions in the background matrix, and on the polarization of the applied electric field. 相似文献
13.
Field electron emission and field desorption of cesium ions from a monatomic graphene film on Ir and graphene clusters in amorphous carbon are investigated using field electron microscopy and continuous-mode field desorption microscopy. The deposition of cesium on amorphous carbon with graphite clusters leads to inversion of the emission (i.e., emission from the emission centers disappears against the back-ground of uniform emission from the previously nonemitting surface). In both systems, ion current pulses are observed during field desorption in a stationary electric field. During field desorption from the graphene film, current pulses of Cs+ ions with a duration shorter than 0.1 s appear from the plane faces of the iridium point. During desorption from graphite clusters, ion current pulses form a pattern of “collapsing rings” on the screen. Possible mechanisms of the observed processes are considered using the model of cesium intercalation by graphite and by the graphene layer and the desorption of Cs atoms under the action of the electric field, as well as the “flip” of the dipole moment during the cesium intercalation. 相似文献
14.
The resonance fluorescence of a degenerate V-type three-level atom in the field of an intense monochromatic wave with arbitrary polarization composition is investigated. The equations of motion, the general form of the radiation relaxation operator, and the analytical expressions for the angular distribution of the intensity of the spontaneous radiation from atoms, and the total intensity of the resonance fluorescence for such systems are obtained. The angular distribution of the spontaneous radiation from atoms for the D line of alkali-metal vapors is investigated. It is predicted theoretically that the intensity of the resonance fluorescence will decrease as the intensity of the pump wave increases in observations in a direction of the electric field vector of the laser wave. 相似文献
15.
Polarization‐independent absorption enhancement in a graphene square array with a cascaded grating structure 下载免费PDF全文
Jun Wu 《Journal of synchrotron radiation》2018,25(2):419-424
The polarization‐independent enhanced absorption effect of graphene in the near‐infrared range is investigated. This is achieved by placing a graphene square array on top of a dielectric square array backed by a two‐dimensional multilayer grating. Total optical absorption in graphene can be attributed to critical coupling, which is achieved through the combined effect of guided‐mode resonance with the dielectric square array and the photonic band gap with the two‐dimensional multilayer grating. To reveal the physical origin of such a phenomenon, the electromagnetic field distributions for both polarizations are illustrated. The designed graphene absorber exhibits near‐unity polarization‐independent absorption at resonance with an ultra‐narrow spectrum. Moreover, the polarization‐independent absorption can be tuned simply by changing the geometric parameters. The results may have promising potential for the design of graphene‐based optoelectronic devices. 相似文献
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采用沉淀法制备了纳米氧化锌粒子,着重对其进行了不同条件(电场强度、极化温度)下的外电场极化处理.以X射线衍射仪和拉曼光谱仪对产物的结构、拉曼位移等进行了表征.测试了氧化锌极化产物在乙醇、丙酮气体中的气敏性能,研究了外电场效应对纳米氧化锌拉曼光谱和气敏性能的影响机制.结果表明,纳米氧化锌样品在外电场中存在着极化电场强度和温度的阈值,当电场强度和温度分别大于9375 V·cm~(-1)和150℃时,纳米氧化锌试片出现明显的漏电现象,极化效应显著降低并消失.在电场强度和温度阈值范围内,外电场极化作用能够导致氧化锌437 cm~(-1)处的拉曼特征峰强度明显降低.随外电场强度和极化温度增加,纳米氧化锌元件在丙酮气体中的灵敏度逐渐升高,在乙醇气体中的灵敏度逐渐降低,即外电场极化可以有效调控纳米氧化锌的气敏选择性. 相似文献
17.
The behavior of graphene bombarded by fullerene(C60 and C70)and its derivatives through using nonequilibrium molecular dynamics method are studied.The microscopic mechanism of passing through graphene is obviously related to the initial structure of destroying carbon-carbon bonds and the strong interaction between the circular region of graphene and the cluster.The probability of passing through graphene depends on the incident velocity of clusters,the species of clusters,the temperature of heat baths,and the defect of graphene.Our results can provide a perspective for further understanding the mechanism of generating nanopores in graphene.The clusters used here may also bring about some potential utilities in tie functionalization of graphene and the production of nanopores. 相似文献
18.
V. I. Konchenkov S. V. Kryuchkov T. A. Nosaeva D. V. Zav’yalov 《Physics of Wave Phenomena》2013,21(1):56-61
For graphene placed in a dc magnetic field and exposed to two electromagnetic waves of the same polarization but different frequencies, an expression for the direct current density in a direction perpendicular to the polarization plane of the waves is derived. The direct current component is nonzero for the wave frequency ratio equal to two; it is proportional to the magnetic field strength, the electric field strength of the higher-frequency wave, and the squared electric field strength of the lower-frequency wave. The physical mechanism of the current generation is similar to the Hall effect. 相似文献
19.
A molecular dynamics simulation of neutral clusters (H2O)
n ≤ 21 has been performed in the framework of the flexible polarized model. The formation and evolution of the dipole moment of
the cluster have been investigated with a change in the size and temperature of the cluster and an external electric field.
It has been shown that at low electric fields corresponding to the experiments on the deflection of clusters in the transverse
inhomogeneous electrostatic field (Moro et al., 2006), the induced polarization of the cluster is determined by the orientational
polarizability of the “rigid” cluster, rather than by the intracluster reorientation of the molecules. The calculated dependence
of the effective polarizability of the cluster in the low field on n qualitatively reproduces the experimental results, but the calculated polarizability is numerically much higher than the
experimental value by, e.g., a factor of 4 for n ≈ 20. 相似文献
20.
Dielectric constants for the Stockmayer fluid are computed both from the equilibrium fluctuations of the polarization and from the polarization response to an applied field in a molecular dynamics simulation with periodic boundary conditions and with the dipole interactions treated by the Ewald method. The dielectric constant at finite wavelength is obtained from a Kirkwood-like expression, while for uniform polarization fluctuations a different expression applies due to the absence of surface effects in the Ewald calculation. The results are nearly independent of the number (up to 500) of particles investigated, even at large values of the dipole moment. The dielectric constants obtained from the approximate solution of the hypernetted chain integral equation are considerably larger than the molecular dynamics results except at low dielectric constants. The external field simulation permits study of the non-linear dependence of the dielectric constant on the magnitude of the applied electric field. 相似文献