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Time-Dependent Local Density Approximation Calculations for Absorption Spectra of Small Carbon Clusters
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Absorption spectra for Cn clusters (n = 2-8) are calculated using an adiabatic time-dependent density functional formalism within the local density approximation (TDLDA). We compare the calculated spectra with those computed using a simple local density approximation approach. It is readily observed that the TDLDA spectra display a significant blue shift with respect to the Kohn-Sham eigenvalue spectra. The calculated spectra exhibit a variety of features that can be used for comparison against future experimental investigations. We also obtain a significant threshold absorption, which can distinguish different ground states of the carbon clusters. 相似文献
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V. S. Vinogradov 《Physics of the Solid State》2010,52(3):568-573
A theory of vibrational spectra of solid solutions proposed by the author has been developed, in which a cluster of n cells statistically filled with impurity atoms is used as a phonon scattering unit. The calculation of vibrational spectra
of a disordered linear chain in the generalized non-self-consistent approximation has demonstrated a strong dependence of
the spectrum on the number n. For n = 6, the calculated spectrum is in an excellent agreement with the result of the computer experiment performed by Dean for
a chain of 8000 atoms. The maximum number of impurities in the cluster to be considered depends on the magnitude of the initial
damping (in real crystals, it is damping due to anharmonicity). The spectrum has also been calculated in the generalized self-consistent
approximation. This calculation gives a smeared structureless curve, which absolutely does not agree either with the theoretical
calculation in the non-self-consistent approximation or with the results obtained by Dean. This means that the generalized
self-consistent approximation overestimates the weight of the incoherent scattering processes, which leads to averaging of
the phases. The spectrum of a three-dimensional solid solution is calculated using a simple model of the crystal. 相似文献
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J. Fandio M.F. García-Snchez G. Santana A. Crespo J.C. Alonso A. Oliver 《Superlattices and Microstructures》2008,43(5-6):454
Gold nanoclusters with diameters up to 50 nm were grown in sandwich structures consisting in 15 nm of plasma deposited silicon nitride, 1 nm of gold grown by sputtering and 15 nm of plasma deposited silicon nitride (SiN/Au/SiN). Previous to the last step, ammonia plasma treatments of the gold surface were carried out with time as the main variable. The resulting structures were analyzed by high resolution transmission electron microscopy and spectroscopic ellipsometry. As a result of plasma treatments, island-like structures of as-grown gold clusters evolve to near spherical-shape features with decreasing diameter as the plasma treatment time rises. Ellipsometric spectra were modeled based on the Bruggeman effective medium approximation and the influence of size and shape of nanoparticles on the optical properties were calculated. 相似文献
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The detailed comparison between static (frozen core) and polarization radiation emission channel in electron-tungsten ions collisions is presented. Both Bremsstrahlung and radiative recombination spectra are calculated for different ion charges Zi and electron energies E. The consideration is based on quasiclassical approach using statistical (Thomas-Fermi) and local plasma frequency models for ion cores as well as rotational approximation for emission spectra. The frequency and energy domains where polarization channel is comparable or even dominates over static one are determined. The results are of interest for modern magnetic fusion investigations of plasmas with tungsten impurity. 相似文献
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《Nuclear Physics A》1997,617(3):316-330
Double-differential cross sections of the 208Pb(n,p) reaction have been measured at 97 MeV in the angular range 0°–30° for excitation energies up to 40 MeV. The experimental proton spectra have been compared with calculated spectra obtained with a statistical multistep direct reaction theory, in which charge exchange and inelastic response functions are described microscopically in the quasiparticle random phase approximation. The direct parts of the spectra have also been distributed on different multipole components by using a decomposition technique, based on sample angular distributions calculated within the distorted-wave Born approximation. 相似文献
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The Landau-Dykhne approximation for the spectrum of above-threshold electrons produced upon ionization of atoms by a monochromatic laser field is used to calculate the spectrum in the case of ionization by a short laser pulse. The spectra obtained in this way are compared with those calculated by the adiabatic theory. The comparison shows that the Landau-Dykhne approximation with the properly chosen exponential factor describes well the averaged spectrum. 相似文献
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G. N. Ten T. G. Burova K. V. Berezin A. A. Yakovleva M. N. Nurlygayanova V. I. Baranov 《Optics and Spectroscopy》2012,113(5):487-494
The structure of the first excited electronic states of indole has been calculated for the isolated state and aqueous solution. The vibrational spectra of isolated indole have been calculated by the DFT method in the harmonic and anharmonic approximations. The resonance Raman spectra of indole have been calculated quantum mechanically in the Herzberg-Teller approximation. The effect of hydrogen bonds on the structure and vibrational (Raman and resonance Raman) spectra of indole has been analyzed. 相似文献
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Nie Yaozhuang Xie Youqing Li Xiaobo Peng Hongjian 《Journal of Physics and Chemistry of Solids》2008,69(4):852-858
A first-principles study of the anisotropic thermal expansion of hcp metals Be and Y is reported. According to quasiharmonic approximation, the phonon spectra were computed at a set of lattice parameters using the pseudopotential plane wave method with the local density approximation in the framework of the density functional perturbation theory. The free energies were obtained according to the calculated phonon spectra and thermal properties such as specific heat at constant volume (pressure) were calculated. The electronic contribution to specific heat was found important to metal Y not only at very low temperature but also over room temperature. The calculated results are in good agreement with available experimental data in a wide range of temperature. 相似文献
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Angle resolved photoemission spectra of Pt(111) were measured along the
direction of the surface Brillouin zone (SBZ). The electronic structure of a semi-infinite Pt(111) crystal was calculated applying the LMTO-TB approximation to aid interpretation of the spectra. The experimental spectra are well described by the calculated bulk band structure. Both the experiment and calculation reveal a surface state near the Fermi level in the neighborhood of the
point of the SBZ. 相似文献
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采用红外椭圆偏振光谱对微波等离子体化学气相沉积法(MPCVD)和热丝化学气相沉积法(H-FCVD)制备的金刚石薄膜在红外波长范围(2.5—12.5μm)的光学参数进行了测量.建立了不同的光学模型,且在模型中采用Bruggeman有效介质近似方法综合考虑了薄膜表面和界面的椭偏效应.结果表明,MPCVD金刚石膜的椭偏数据在模型引入了厚度为77.5nm的硅表面氧化层、HFCVD金刚石膜引入879nm粗糙层之后能得到很好的拟合.最后对两种模型下金刚石薄膜的折射率和消光系数进行了计算,表明MPCVD金刚石薄膜的红外
关键词:
金刚石薄膜
红外椭圆偏振光谱
光学参数
有效介质近似 相似文献
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The energy spectra of single-wall carbon nanotubes (CNTs) with chiralities of (10, 10), (11, 9), and (12, 8) are calculated in the static fluctuation approximation for the Hubbard model. The choice of these systems for investigation was dictated by the fact that these systems are the most typical of heterogeneous samples obtained by synthesis. It is shown that in the chosen model and approximation, the type of conduction is independent of chirality, which contradicts the generally accepted opinion concerning the critical dependence of the CNT conduction current on the chirality indices. The optical absorption spectra of the CNTs under investigation are calculated using the resultant energy spectra. The shape of the optical absorption spectrum averaged over the known weight composition is in good agreement with experimental data. The results of investigation suggest that the rule according to which CNTs exhibit metal-type conductivity when the difference in the chirality indices is a multiple of three; otherwise, they have the semiconductor-type conductivity, is in all probability not general, but has applicability limits that can be established by rigorous calculations based on the Hubbard model. 相似文献
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The structure of the excited states and absorption spectra of butadiene, hexatriene, and octatetraene are calculated by the parametric method of the theory of vibronic spectra using models of the first-and second-order approximations. It is shown that these molecular models adequately reflect the molecular structure and allow one to predict quantitatively the shape and fine vibrational structure of the absorption spectra. When passing to the second-order approximation, only two additional (angular) parameters are used. These parameters are transferable in the series of polyenes. Compared to the first-order approximation model, the second-order approximation model more accurately takes into account the angular deformations of polyenes upon their excitation and describes the intensity distribution in the vibrational spectrum, including weak lines. In addition, the calculations also quantitatively predict spectral variations in the molecular series. The parametric method is more efficient for modeling polyatomic molecules in the excited states and their vibrational spectra compared to other semiempirical and ab initio methods. 相似文献
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The coupled plasmon-LO-phonon and single-particle excitations of a photocreated electron-hole plasma in high purity GaAs are studied by means of Raman scattering measurements. The experimental results are described by the random-phase approximation with respect to the multicomponent character of optical plasma. From single-particle spectra the plasma distribution function and drift velocities up to 107 cm/s have been determined. Using the coupled modes as probe for the plasma density the temperature dependence of the recombination in the EHP is studied. 相似文献
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In an approximation of the generalized valence force field, the frequencies and forms of the normal vibrations of the free
molecule of spiroanthraceneoxazine (SAO) are calculated. The vibrational spectra of SAO are measured: the IR absorption spectra
in an NaCl disk and the Raman spectra in a KBr disk. The calculated and experimental data were correlated with the aid of
a method of refined initial data. The results obtained agree with the calculated and experimental spectra of model and related
compounds.
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Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 72, No. 5, pp. 576–571, September–October, 2005. 相似文献
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通过测量纳米磷化镓(GaP)粉体在紫外可见光波段(200-800nm)的反射光谱,运用三流理论由反射光谱计算出纳米GaP粉体的吸收系数(Ea)和散射系数(Es)的比值(Ea/Es)。纳米GaP粉体的反射光谱的形状主要受吸收的影响,即GaP禁带结构的影响。 相似文献
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The electronic structure of titanium monoxide TiO y (0.810 ≤ y ≤ 1.262) in the high-temperature cubic phase with vacancies randomly distributed over the titanium and oxygen sublattices is calculated in the coherent potential approximation. The changes in the electronic spectra with the concentration of vacancies are retraced. The calculated spectra are compared to the available experimental data. 相似文献