Ar-H2(D2, T2)碰撞体系的振转相互作用势及散射截面的理论计算

用量子力学从头算的耦合族CCSD(T)方法, 使用相关一致基组aug-cc-pV5Z并加3s3p2d1f1g高斯键函数计算了Ar原子与H₂分子的振转相互作用和电荷分布, 采用Boys和Bernardi提出的均衡法消除了基组重叠误差(BSSE). 然后用Tang-Toennies势能函数拟合得到Ar-H₂体系相互作用势的解析表达式. 在该相互作用势下, 用密耦方法计算了Ar原子入射能量为83 meV时, Ar-H₂(D₂, T₂)碰撞体系的散射截面. 计算Ar-D₂体系的微分截面与实验值比较符合很好. 计算结果及分析表明, 在长程吸引势的散射中, 色散能起主要作用; 在短程排斥势的散射中, 交换能起重要作用. 当碰撞参数在0.27 nm至0.47 nm的范围时, Ar-H₂(D₂, T₂)碰撞体系的径向偶极发生两次转向.     

低能电子与氢分子碰撞的振动激发积分散射截面的研究

采用振动密耦合方法,研究了低能电子与H₂分子碰撞的振动激发积分散射截面.研究表明,使用18个Morse振动波函数、5个分波和4个对称性可以得到收敛的0→0,0→1,0→2和0→3积分散射截面;而且振动波函数的性质和振动能级的精确性会直接影响振动激发散射势能和振动激发积分散射截面.计算结果与实验符合得很好. 关键词： 电子散射 振动激发 2分子')" href="#">H₂分子 积分截面     

Ne-HF体系的相互作用势及散射截面的密耦计算

利用非线性最小二乘法拟合在CCSD(T)/aug-cc-pVQZ理论水平下计算的相互作用能,得到了基态Ne-HF体系相互作用势的解析表达式.基于拟合的CCSD(T)势,通过密耦计算得到了入射能量分别为60,75,100和150meV 时,Ne-HF散射的微分截面和分波截面,详细讨论了散射截面随能量的变化趋势以及态-态激发截面对总非弹性散射截面的影响. 关键词： 相互作用势 散射截面 密耦计算 Ne-HF体系     

20 Ne(34 Ne)原子与18 Na2(23 Na2,37 Na2)分子低温下冷碰撞的同位素效应研究

本文用多体刚性椭球模型计算了相对入射能量为190 meV时,氖的同位素原子²⁰Ne,³⁴Ne与钠的同位素分子¹⁸Na₂,²³Na₂,³⁷Na₂ 替代碰撞体系的态态转动激发积分散射截面和总转动激发积分散射截面,在此基础上计算并分析了相互作用势的不同区域对²⁰Ne-¹⁸Na_{2关键词： 多体刚性椭球模型 转动激发积分散射截面 钠同位素分子 椭球等势面}     

基于严格交换势的低能电子与H2分子碰撞振动激发散射截面的研究

严格交换势用于研究低能电子与H₂分子的弹性和非弹性散射截面,线性代数方法和R-矩阵传播子相结合求解基于振动密耦合方法的积分-微分耦合方程组,由此得到收敛的(0→0,0→1,0→2)散射微分截面和积分截面.理论计算结果与目前优秀的实验值和其他理论计算值进行了比较,表明基于振动密耦合方程的严格交换势在低能电子与H₂分子振动激发散射中有重要作用. 关键词： 严格交换势 2分子振动激发')" href="#">H₂分子振动激发 微分截面 积分截面     

球形粒子之间的声相互作用

本文讨论某种介质(其中包括许多球形粒子,例如浓悬浮体)对平面波的散射问题,计算了粒子之间的声相互作用场,从而得到了粒子的等效散射截面。当粒子大小比声波波长小很多时,可有如下的结论:(1)由于声相互作用,一个粒子的散射截面只有原来的Q倍,从几何上看,这是由于粒子的互相遮蔽的结果,其遮蔽因子为Q= |1-(γ₀A₀⁽¹⁾+γ₁A₁⁽¹⁾|²;(2)考虑到相互作用之后,散射系数与浓度不再是线性关系;(3)当粒子的尺度比声波波长小很多但比粘滞波波长大很多时,相互作用之后粒子的散射系数与频率的关系仍服从瑞利散射。但当粒子半径接近或小于粘滞波波长时,散射系数与频率的关系比四次方要高。 关键词：     

耦合广义非线性薛定谔方程的相互作用表象龙格库塔算法及其误差分析

本文通过表象变换, 将耦合广义非线性薛定谔方程 (C-GNLSE) 变换成相互作用表象中的向量方程, 再利用向量形式的4阶龙格-库塔迭代格式, 建立了一种在频域内求解C-GNLSE的同步更新迭代算法. 通过将该向量形式的相互作用表象中的4阶龙格-库塔 (V-JH-RK4IP) 算法应用于高双折射光子晶体光纤中超连续谱产生的数值模拟, 验证了算法的有效性, 通过与现有其他典型算法的比较, 表明以V-JH-RK4IP算法求解C-GNLSE具有最高的计算精度和计算效率. 关键词： 耦合广义非线性薛定谔方程(C-GNLSE) 相互作用表象 4阶龙格-库塔算法 超连续谱产生     

三维目标与粗糙面复合散射的广义稀疏矩阵平面迭代及规范网格算法

提出了快速计算二维导体粗糙面与面上金属目标复合散射的广义稀疏矩阵平面迭代及规范网格法(G-SMFSIA/CAG).推导了二维导体粗糙面与面上目标相互作用的耦合积分方程,用稀疏矩阵平面迭代及规范网格法(SMFSIA/CAG)求解粗糙面部分的表面积分方程,而用基于RWG基函数的矩量法(MOM)计算目标部分的表面积分方程,并通过更新方程的激励项迭代求解目标与粗糙面的相互耦合作用.结合Monte-Carlo方法产生具有PM(Pierson-Moskowitz)海浪谱的随机海洋粗糙面,数值分析了海面上不同形状导体目 关键词： 复合散射 广义稀疏矩阵平面迭代及规范网格法 随机海洋粗糙面 双站散射系数     

两体组合坐标表象的建立、性质及应用

为了研究具有相互作用势和运动耦合的两个非全同的量子谐振子体系的动力学问题,利用有序算符乘积内的积分技术,建立了一种两粒子体系的组合坐标新表象|η₁,η₂〉,构造了一个双模压缩算符U并分析了其压缩特性. 应用组合坐标新表象严格求解了具有相互作用势和运动耦合的两个非全同的量子谐振子体系的动力学问题. 这为研究复杂耦合量子谐振子体系提供了一个有效途径. 关键词： 有序算符乘积内的积分技术 组合坐标表象 双模压缩算符 幺正矩阵     

时域小波Galerkin法在有耗地面与任意目标复合散射中的应用

采用时域小波Galerkin(WGTD)方法计算了有耗地面与三维目标的复合散射,其中连接边界采用三波法.得到近场数据后,为避免复杂的Sommerfeld积分用互易原理简化了外推过程.计算了地面目标的雷达散射截面,验证了WGTD方法的精度和有效性.与时域有限差分方法相比,WGTD方法具有色散线性好、节省内存、计算速度快等优点. 关键词： 时域小波Galerkin法 复合散射 有耗半空间     

Molekularstrahlmessungen von Stoßquerschnitten für Übergänge zwischen definierten Rotationszuständen zwei-atomiger Moleküle

Previously reported experimental results for inelastic cross sections for rotational excitation of TlF molecules in low-lying, well defined rotational states are interpreted in terms of a time dependent perturbation theory formulation of the high energy approximation. In order to calculate inelastic cross sections for the observed small angle scattering the Born approximation and the classical deflection function are shown to be applicable. In this approximation the ΔJ selection rules are characteristic of the individual terms in the expansion of the potential, whereas the ΔM selection rules depend on the orientation of the molecule with respect to the scattering trajectory. An approximation for dealing with a scattering gas consisting of molecules is introduced and the appropriate orientation averaging is carried out for the case of a generalized electrostatic potential. The measured results for the transition TlF(2.0)→ (3.0) in collisions with the rare gases and CH₄ and SF₆ are more than a factor three larger than calculated results for the induced dipole-quadrupole (α, μ, Q) interaction. Rough argeement is found between calculated results for a dipole-quadrupole interaction and the experimental results for the above mentioned transition produced by the scattering gases O₂, N₂ (air), N₂O, and H₂O. Finally, the dipole-dipole potential appears to provide an explanation for the large inelastic cross sections observed with NH₃ and CF₂Cl₂. Calculated inelastic and total cross sections are however considerably larger (about a factor 2) than the measured results with NH₃. Possible explanations are discussed.     

Radiative corrections to low-energy ππ scattering

Radiative corrections to low-energy ππ scattering are calculated. A chiral SU(2) × SU(2) Lagrangian is used to describe low-energy scattering. This strong interaction Lagrangian is modified in the presence of the electromagnetic field in a gauge invariant way. It is found that photons do not probe the strong vertex. Corrections to the cross sections are calculated to O(α). All the ultra-violet divergences cancel, and the results are independent of cut-off parameters. Corrections to the Weinberg scattering lengths of the order of 1% are defined by removal of the Coulomb pole terms. The field theoretic calculation is compared with a potential theory approach. It is argued that the potential theory calculation of radiative corrections is more reliable.     

Local atomic ordering in nickel based Ir and Rh alloys

Experimental measurements of the diffuse X-ray scattering are performed on alloys of Ni with Rh and Ir. The atomic short range order (SRO) parameters α_i are calculated from the measured intensity. The existence of SRO is established in the two systems. The values of α₁ are observed to have anomalously large negative values for all the samples.The experimental data so obtained is interpreted theoretically by calculating the interaction energies on the basis of electronic theory of ordering. Theoretically calculated values of interaction energies are found to be in agreement with the experimentally determined type of order in these alloys.     

He-N2碰撞体系散射截面的理论研究

本文运用量子化学从头计算MP2方法6-311 G(3df,2p)基组,计算了He-N2相互作用的势能,拟合出He原子与N2分子相互作用的各向异性势函数,其势函数参数:势能球平均势阱位置、势阱深度、势能零点位置与通过散射实验数据分析的ESMSV(Exponential-Spline-Morse-Spline-Van der waals)势比较吻合.然后,用公认精确度高的密耦方法计算了He原子与N2分子碰撞体系的总微分截面、弹性微分截面、转动激发的非弹性微分截面和积分截面,计算结果与实验数据符合得较好.     

Phonon response of the high‐temperature spin‐density‐wave superconductors

The phonon response of a spin density wave superconductor (SD^W-SC) is calculated. The phonon self energy due to electron-phonon interaction, which involves the electronic density response function, is evaluated explicitly for the coexistent SDW-SC state. It has a square-root singularity at a frequency corresponding to the superconducting gap 2Δ. As a consequence, the spectral density function of the SDW-phonon will show a peak at 2Δ The possibility of observing the 2Δ-peak by Raman scattering is discussed. The relevance of the results to high-temperature superconductors is pointed out. The available Raman data for YBa₂Cu₃O_7-δare compared with the results of the calculation.     

A Monte Carlo model for determination of binary diffusion coefficients in gases

A Monte Carlo method has been developed for the calculation of binary diffusion coefficients in gas mixtures. The method is based on the stochastic solution of the linear Boltzmann equation obtained for the transport of one component in a thermal bath of the second one. Anisotropic scattering is included by calculating the classical deflection angle in binary collisions under isotropic potential. Model results are compared to accurate solutions of the Chapman–Enskog equation in the first and higher orders. We have selected two different cases, H₂ in H₂ and O in O₂, assuming rigid spheres or using a model phenomenological potential. Diffusion coefficients, calculated in the proposed approach, are found in close agreement with Chapman–Enskog results in all the cases considered, the deviations being reduced using higher order approximations.     

Coupled cluster ab initio potential energy surfaces for CO… He and CO… H2

Ab initio potential energy surfaces including the vibrational coordinate dependence are presented for CO… He and CO… H₂ using the coupled cluster method with Brueckner orbitals. The interaction energy is calculated using the supermolecule approach. The calculation of rate constants for the vibrational relaxation of CO(v = 1) by He and their comparison with the experimentally measured values over the temperature range 40–300 K is used to test the accuracy of the CO… He surface. Comparison with results from an earlier surface calculated by symmetry adapted perturbation theory shows that the two surfaces have similar scattering characteristics and reproduce the experimental measurements to a similar level of accuracy. The potential surface for the CO… H₂ system is presented as raw data in anticipation of future calculations.     

Long-range coulomb interaction in ionic crystals

Expressions have been proposed for calculating the matrix elements of the Coulomb interaction of p and d electrons in a chosen ion of a crystal with an infinite crystal lattice. The matrix elements have been calculated at Gaussian-type orbitals. The Coulomb interaction energy per molecular unit of the ????-NaV₂O₅ crystal has been calculated in the ionic approximation for homogeneous and chain orderings. It has been shown that the more correct determination of the energetic favorability of one or other ordering requires calculation of the Coulomb interaction energy with an infinite crystal lattice of electrons that are at different orbitals of the ion under consideration.     

Density and thermodynamics of hydrogen adsorbed on the surface of single-walled carbon nanotubes

A method is proposed for calculating the adsorption of hydrogen in single-walled carbon nanotubes. This method involves solving the Schrödinger equation for a particle (hydrogen molecule) moving in a potential generated by the surrounding hydrogen molecules and atoms forming the wall of the carbon nanotube. The interaction potential for hydrogen molecules is taken in the form of the Silvera-Goldman empirical potential, which adequately describes the experimental data on the interaction between H₂ molecules (including the van der Waals interaction). The interaction of hydrogen molecules with carbon atoms is included in the calculation through the Lennard-Jones potential. The free energy at a nonzero temperature is calculated with allowance made for the phonon contribution, which, in turn, makes it possible to take into account the correlations in the mutual arrangement of the neighboring molecules. The dependences of the total energy, the free energy, and the Gibbs thermodynamic potential on the applied pressure P and temperature T are calculated for adsorbed hydrogen molecules. These dependences are obtained for the first time with due regard for the quantum effects. The pressure and temperature dependences of the hydrogen density m(P, T) are also constructed for the first time.     

A comparative multi-property analysis of existing models for the He–N2 potential energy surface

The ability of an improved version of a recent three-dimensional ab initio potential energy surface for the He–N₂ interaction [Phys. Rev. A 66, 042703 (2002)], determined from high-level coupled-cluster calculations (including full singles and doubles, perturbative triples, and Brueckner orbitals), to predict scattering cross-sections and various bulk gas mixture properties is tested. The full three-dimensional potential energy surface has been employed for the calculation of vibrational relaxation rates, and a two-dimensional version (at a fixed N₂ bond length of 2.0743 a ₀) has been used for the calculation of molecular beam scattering cross-sections using quantum close-coupling methods and for the calculation of bulk gas phenomena using classical trajectory methods. The results obtained from the two-dimensional version of the present potential energy surface are compared with those obtained from three other recent accurate two-dimensional representations of the He–N₂ interaction.