共查询到19条相似文献,搜索用时 78 毫秒
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朱正和 《原子与分子物理学报》2012,29(6)
只有由群的对称性才可能导出每个不可约表示的对称性波函数, 即对称化基函数.也只有由群的对称性才可能导出电子状态跃迁的最一般选择定则 , 即电偶极跃迁E1, 电四极跃迁E2 和 电八极跃迁E3跃迁的选择原则. 本文以 和 为例, 导出电多积跃迁的选择原则. 角动量的选择定则只是特例. 并用方法SAC-CI/6-31G 计算了 H2O和 CC的基态以及其激发态的激发能和振子强度.本文只适合单光子过程. 计算都与理论相合. 相似文献
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包含小型固态器件的介观电路因其易于集成、可大规模化的特点,在众多可能实现量子计算的方案中备受关注。本文利用正则量子化方法,给出了含有复杂耦合的介观LC电路的量子化方案,得到了该系统的能量算符;通过与一维量子谐振子相类比,并借助于幺正变换,导出了系统的能级公式及其态矢量表达式。在此基础上,讨论了介观电路两支路中电容器某一极板上的电荷量及穿过两线圈的等效磁通量在基态下的均方量子涨落。另外,考虑到一旦受到外电磁场的辐照,介观电路的状态将会改变,并可在相应能级之间发生跃迁,利用“不变本征算符”方法,得到了该系统能级跃迁的选择定则。 相似文献
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本文从非线性光学中辐射跃迁速率的表达式出发,在全量子理论下,导出了半导体中任意阶多光子吸收跃迁速率的一般表达式。理论分析结果表明,n光子吸收跃迁速率与光强的n次方和n阶光子相干度成正比。本文在多能带及二能带理论模型下,对多光子吸收跃迁速率的一般表达式进行了化简,并对非线性相互作用项对跃迁速率的贡献,作了讨论。 相似文献
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证明频率为v的辐射引起的量子跃迁中,跃迁系统始末两态能量差不必是hv的整数倍。跃迁的玻尔条件和光电效应的爱因斯坦定律都是微扰近似的结果,在强激光引起的跃迁中不成立。We prove that in the quantum transition of a system induced by the radiation of frequency v, the energy difference between the initial and the final states of the system is not necessarily being an integer multiple of hv. The Bohr condition for quantum transitions and the Einstein law for photo-electric effects are approximate results of perturbation. They are violated in the transitions induced by intense lasers. 相似文献
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《Molecular physics》2012,110(19-20):2455-2464
The well-known natural orbitals are defined as eigenfunctions of a one-particle reduced density operator, and can be obtained from a computed density matrix by diagonalization. Similarly, in this article we define the binatural orbitals, which are obtained for a pair of wave functions by a singular value decomposition of a reduced transition density matrix. The pair of states would usually be eigenstates of the electronic Hamiltonian, and the binatural orbitals then serve as a useful tool for the analysis of the transition between these states. More generally, application to any two state functions gives important information as to how the two states differ. Some examples are shown. 相似文献
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The valley valve effect was predicted in a straight zigzag graphene nanoribbon (ZGR) p/n junction. In this work, we address a possible valley selection rule in a Y-shaped ZGR junction. By modeling the system as a three-terminal device and calculating the conductance spectrum, we found that the valley valve effect could be preserved in the system and the Y-shaped connection does not mix the valley index or the pseudoparities of quasiparticles. It is also shown that the Y-shaped ZGR device can be used to separate spins in real space according to the unchanged valley valve effect. Our finding might pave a way to manipulate and detect spins in a multi-terminal graphene-based spin device. 相似文献
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The black-box fast multipole method 总被引:1,自引:0,他引:1
A new O(N) fast multipole formulation is proposed for non-oscillatory kernels. This algorithm is applicable to kernels K(x,y) which are only known numerically, that is their numerical value can be obtained for any (x,y). This is quite different from many fast multipole methods which depend on analytical expansions of the far-field behavior of K , for |x-y| large. Other “black-box” or “kernel-independent” fast multipole methods have been devised. Our approach has the advantage of requiring a small pre-computation time even for very large systems, and uses the minimal number of coefficients to represent the far-field, for a given L2 tolerance error in the approximation. This technique can be very useful for problems where the kernel is known analytically but is quite complicated, or for kernels which are defined purely numerically. 相似文献
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Thomas Vojta 《Annalen der Physik》2000,9(6):403-440
Quantum phase transitions occur at zero temperature when some non‐thermal control‐parameter like pressure or chemical composition is changed. They are driven by quantum rather than thermal fluctuations. In this review we first give a pedagogical introduction to quantum phase transitions and quantum critical behavior emphasizing similarities with and differences to classical thermal phase transitions. We then illustrate the general concepts by discussing a few examples of quantum phase transitions occurring in electronic systems. The ferromagnetic transition of itinerant electrons shows a very rich behavior since the magnetization couples to additional electronic soft modes which generates an effective long‐range interaction between the spin fluctuations. We then consider the influence of rare regions on quantum phase transitions in systems with quenched disorder, taking the antiferromagnetic transitions of itinerant electrons as a primary example. Finally we discuss some aspects of the metal‐insulator transition in the presence of quenched disorder and interactions. 相似文献
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On an example of a simple spin system with two ground states and no symmetry, we show how to control low-temperature systems near first-order phase transitions by a straightforward renormalization group argument. The method, as opposed to the Pirogov-Sinai approach, also works for complex Hamiltonians. 相似文献
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