Lineshape theory of the plasmon-phonon sidebands of a semiconductor plasma gain spectrum

The gain spectrum of an electron-hole plasma in direct-gap semiconductors due to plasmon-phonon-assited radiative transitions is calculated for various plasma densities at zero temperature. The screened Coulomb interaction is treated within a damped plasmon-phonon-pole approximation. The validity of this approximation is checked in the simpler case without phonon participation by comparing it with the dynamical random-phase approximation (RPA). For CdS the calculated spectra are in good qualitative agreement with the spectra experimentally observed by Saito.     

CALCULATION OF THE FIXED LENGTH FUNDAMENTAL su(2) HIGGS MODEL

The phase diagram of the lattice system of SU(2) gauge field coupled with the fixed length Higgs field in fundamental representation has been calculated by the variational-cumulant expansion method to the third order approximation.The method of determining the variational parameter has been improved by using the free energy to the second order approximation.Thus calculated phase diagram is in good agreement with the Monte Carlo estimation and the order of the phase transition is clearly determined in the third order approximation.     

双原子分子非谐振转波函数和能级

从双原子分子简谐势近似波函数出发,运用微扰理论计算出了双原子分子在非谐振转相互作用下的一级、二级近似能级和一级近似波函数.     

二维伊辛模型相变临界点温度的模拟计算

用计算模拟方法计算了二维伊辛模型的相变临界点温度,其结果接近严格解,明显布喇格－威廉斯近似和贝特近似的结果。     

利用鞍点近似法计算串音对阵列波导光栅复用器性能的影响

基于光的波动性,考虑信号和串音偏振态,改进了鞍点近似法的数学模型,计算了阵列波导光栅复用器的误码率和功率代价,并与高斯近似法和实验结果进行了比较,显示出较高的计算精度。     

Calculations of total ionization cross sections of Ne,Ar, Kr,and Xe atoms in the born approximation allowing for electron perturbations in the continuous spectrum

Electron impact ionization cross sections of Ne, Ar, Kr, and Xe atoms are numerically calculated. The electron perturbation in the continuous spectrum in the target field is taken into account. The matrix elements are calculated in many-electron, nonrelativistic approximation with allowance for the superposition of configurations and relaxation effect. The radial part of the electron wave function in the continuum is calculated by solving the single-configuration Hartree-Fock equation. The wave functions of electrons in the continuum are orthogonalized with respect to the core orbital functions. The calculated cross sections are compared to the experimental data and calculations made using the plane-wave Born approximation and that involving generalized oscillator strengths.     

类硼离子的电子碰撞电离截面

运用扭曲波玻恩交换近似对处于Hartree-Fock基态的类硼离子的电子碰撞直接电离截面进行了计算。电离过程中直接电离与交换电离振幅的干涉有重要的贡献。研究结果表明“自然相因子”近似比“最大干涉”近似要好。后者用于其它离子种类的计算与实验符合很好。同Moores等人的Coulomb-Born近似计算相比较,我们的计算结果与现有的实验数据符合有改进。 关键词：     

A theory of vibrations of solid solutions with inclusion of the cluster effects: Non-self-consistent and self-consistent approximations

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.     

Lattice dynamics and phase diagram of aluminum at high temperatures

The dispersion of phonons in the fcc, hcp, and bcc phases of aluminum is calculated at ultrahigh pressures by the method of small displacements in a supercell. The stability of the phonon subsystem is studied. The thermodynamic characteristics are calculated in the quasi-harmonic approximation, and a phase diagram of aluminum is plotted. As compared to the Debye model, the use of a phonon spectrum calculated in the quasi-harmonic approximation significantly broadens the hcp phase field and strongly shifts the phase boundary between the fcc and bcc phases. The normal isentrope is calculated at megabar pressures. It is shown to intersect the fcc-hcp and hcp-bcc phase boundaries. The sound velocity along the normal isentrope is calculated. It is shown to have a nonmonotonic character.     

计算半导体平板微腔自发发射的近似方法

引入新变量,并利用高阶泰勒展开完成半导体平板微腔自发发射的空间积分,由此得到半导体平板微腔TE模式自发发射的近似表达式.在腔长为半个中心波长和高反射率腔面的半导体平板微腔中,结合电子和空穴的费米分布函数,用近似方法计算垂直方向小角度内自发发射谱和总的自发发射谱,分别与数值空间积分基本相同,可以用于计算量子阱平板微腔自发发射谱.     

Approximations relating to strictly regular mixtures

The approximation of Kikuchi for strictly regular mixtures is simplified, generalized and applied to four types of lattice. The dependence on temperature of the compositions of co-existing phases below the critical temperature is calculated according to Kikuchi's approximation and compared with that given by the quasi-chemical approximation.     

Linear approximation in classical scattering by a moliégre potential

Abstract

In the context of a Monte Carlo simulation of channeling, it is shown how the scattering angle of an ion by a Molière potential can be calculated by linear interpolation. In the case of impulse approximation, this reduces the computing time to ?1/17 of that needed by the usual procedure.

The maximum error introduced by the linear approximation is calculated as a function of the interval width used for interpolation. Using Firsov's inversion formula, the corresponding approximation to the atomic potential is also evaluted. It is shown that such approximation is very good, if compared with the present knowledge of atomic potential.     

Exact analysis of a balanced receiver for differential phase-shift keying signals

The performance of differential phase-shift keying signals with a balanced receiver is exactly analyzed by using a closed-form expression without approximation. The numerical results are well matched with previous results based on the saddle-point approximation. The error probability is calculated exactly using the well-known Marcum Q function.     

Determining the applicability boundaries of small-angle approximation solutions to the radiative transfer equation for elastic peak electron spectroscopy

The nonlinear term of the radiative transfer equation is considered in the small-angle approximation. Angular distributions of electrons elastically scattered from semi-infinite Au and Be samples are calculated. The error introduced by calculating flows of electrons elastically scattered from a semi-infinite target in the small-angle approximation is estimated.     

Plane wave born cross sections including exchange forK-shell ionization of light atoms

Cross sections forK-shell ionization by electron impact have been calculated in plane wave Born approximation (PWBA) including outer screening with allowance for electron exchange in Ochkur approximation. The results agree reasonably with available experimental data.     

A comparison of density-functional-theory and coupled-cluster frequency-dependent polarizabilities and hyperpolarizabilities

The frequency-dependent polarizabilities and hyperpolarizabilities of HF, CO, H₂O and para-nitroaniline calculated by density-functional theory are compared with accurate coupled-cluster results. Whereas the local-density approximation and the generalized gradient approximation (BLYP) perform very similarly and overestimate polarizabilities and, in particular, the hyperpolarizabilities, hybrid density-functional theory (B3LYP) performs better and produces results similar to those obtained by coupled-cluster singles-and-doubles theory. Comparisons are also made for singlet excitation energies, calculated using linear response theory.     

Review of the characteristic effective medium approximation: Fundamentals and use in calculating the optical properties of ultrathin layer structures

This article presents a review of several aspects of the characteristic effective medium approximation that has been used to calculate the optical properties of ultrathin multilayer systems treated as one uniform layer with a single set of effective optical constants. The method, applied for normal incidence, enables one to represent any layer stack by one characteristic matrix whose elements are functions of the structure effective optical constants, stack thickness, and wavelength of the incident light wave. The error between values of the optical properties of a layer system calculated by the standard characteristic matrix technique and those calculated by the characteristic effective matrix approximation can be used as a criterion for establishing a limit beyond which the validity of the approximation could be compromised. As part of this grand review, calculations of the optical properties for normal incidence for numerous layer systems that were reported earlier in separate communications, are reviewed and analyzed.     

Calculation of Four-Quark Condensate Beyond Vacuum Saturation Approximation

Based on a modification of theaglobal color symmetry model, we have calculated the four-quark condensate beyond vacuum saturation approximation by including the contribution of r and u mesons. The numerical results show that there is a sizeable correction of the four-quark condensate in comparison with its factorized value using the vacu urn saturation approximation.     

Light Propagation in an Inhomogeneously Absorbing Medium: Near Field of GaAs-Light Emitting Diodes

The light propagation in media with inhomogeneous absorption is investigated by solving the wave equation in the approximation of very short wavelengths. The lowest order correction of the straight-on light propagation is given. In the approximation of light rays the near-field intensity of a light emitting diode (LED) is calculated by using a special absorption function within the region of light excitation.     

Application of a uniform semiclassical theory to the multiple Coulomb excitation of heavy ions

Transition probabilities of classically allowed multiple Coulomb excitation of deformed heavy nuclei induced by heavy ions are calculated within a uniform semiclassical approximation. It is found that a Bessel uniform approximation is necessary and that caustics have to be treated carefully.