共查询到19条相似文献,搜索用时 0 毫秒
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本文用Matsubara和Toyozawa的locator展开方法重新推导单粒子和双粒子格林函数的相干势近似(CPA)方程,文中不采用对累积量做自洽处理的方法来考虑原子之间的体积排斥效应,而采用Yonezawa早先提出的一种图形法,本文的重点是提出一个可以用来生成单格点图形自洽方程的系统方法,并用在处理双粒子平均格林函数上,这种处理方法可以推广到处理包括液态金属或非晶态金属等具有短程序系统电导率的CPA方程。
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本文推广应用CPA方法来计算由多层无序合金膜组成的超晶格的声子结构.仅考虑合金膜内的质量无序,而对力常数的无序采用虚晶(Virtual Crystal)近似,我们计算了无序超晶格的结构平均声子格林函数的自能及声子态密度曲线,并由此对无序引起该种材料振动模式的变化作了定性的分析. 相似文献
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本文在紧束缚模型内得到了液态金属和非晶态中电子电导率的相干势近似(CPA)结果,用文献[4]提出的处理单格点图形的系统方法可以得到平均双粒子格林函数的近似方程,这里采用具有短程序的点阵-气体模型,液态金属和非晶态金属相对应的CPA方程可以从点阵-气体模型的极限求得,这样得到的目洽方程包括所有的单格点图形,具有CPA的所有性质。
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H. W. Diehl 《Zeitschrift für Physik B Condensed Matter》1977,27(2):189-197
A model with random 1-, 2-, and 3-point potentials is used to study the elementary excitations in substitutionally disordered crystals. The equations of motion for the 1- and 2-point Green's functionsG(1),G(12) are derived and averaged over the ensemble of random configurations. An extension of the coherent potential method is proposed, which leads to a self-consistent set of equations for the averaged 1- and 2-point Green's functions, including corresponding conditional averages. The theory takes into account that randomness effects the anharmonic interactions both via the explicit configuration dependence of the cubic vertices and via the implicit dependence through the Green's functions. The final equations take a similar form as in the usual CPA if the harmonic potential of the pure system and the harmonic single-site impurity potential are replaced by corresponding functionals of averaged and conditionally averaged 1- and 2-point functions, and the definition of the single-site mass-operator is appropriately generalized.Work supported by the Deutsche ForschungsgemeinschaftExtract from thesis, D 26 相似文献
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Berciu M 《Physical review letters》2006,97(3):036402
We present a new, highly efficient yet accurate approximation for the Green's functions of dressed particles, using the Holstein polaron as an example. Instead of summing a subclass of self-energy diagrams (e.g., the noncrossed ones, in the self-consistent Born approximation), we sum all the diagrams, but with each diagram averaged over its free propagators' momenta. The resulting Green's function satisfies exactly the first six spectral weight sum rules. All higher sum rules are satisfied with great accuracy, becoming asymptotically exact for coupling both much larger and much smaller than the free particle bandwidth. Possible generalizations to other models are also discussed. 相似文献
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Moshiour RahamanKartick Tarafder Biplab SanyalAbhijit Mookerjee 《Physica B: Condensed Matter》2011,406(11):2121-2125
We propose and briefly describe the generalized recursion in augmented space using a minimal TB-LMTO basis set for the calculation of configuration averaged current response functions in disordered binary alloys. Since disorder in the current terms is off-diagonal and non-separable, single-site mean-field approaches are unable to deal with it without further approximations. The augmented space approach is ideally suited for such situations and the generalized recursion proposed by Viswanath and Müller provides a fast and accurate O(N) technique for the actual calculations of the configuration averaged susceptibilities. We have applied the method to the disordered FeCo alloy. The results agree reasonably well with available experimental data on ordered versions of both the alloy systems, with extra broadening due to disorder induced lifetime effects. 相似文献
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The one-dimensional tight-binding model and the Green's function method are used to study the chemisorption energy of an atomic H on disordered binary alloys within the average T-matrix approximation. The one-electron chemisorption theory is used to describe the chemisorption process. The chemisorption energy is calculated as a function of the concentration percentages of the two components of the disordered binary alloys. The effect of the surface segregation of the CuNi system is also investigated. 相似文献
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Franz Wegner 《Zeitschrift für Physik B Condensed Matter》1979,35(3):207-210
An apparently overlooked symmetry of the disordered electron problem is derived. It yields the well-known Ward-identity connecting the one- and two-particle Green's function. This symmetry and the apparent shortrange behaviour of the averaged one-particle Green's function are used to conjecture that the critical behaviour near the mobility edge coincides with that of interacting matrices which have two different eigenvalues of multiplicity zero (due to replicas). As a consequence the exponents of the d.c. conductivity is expected to approach 1 for real matrices and 1/2 for complex matrices as the dimensionality of the system approaches two from above. In two dimensions no metallic conductivity is expected. 相似文献
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Prabhakar P Singh 《Pramana》1996,47(2):99-108
Using the atomic-sphere approximation formulation of the Korringa-Kohn-Rostoker coherent potential approximation (KKR CPA)
method, we have studied the effects of relativity on the electronic structure of ordered and substitutionally disordered Ni-Pt
alloys. The inclusion of mass-velocity and Darwin terms are found to be essential for describing the experimentally observed
ground-state properties. For the stability of disordered Ni-Pt alloys we find that, in addition to relativity, the minimization
of charge-transfer effects are important. We also find that the treatment of ordering tendencies based on the band energy
term alone is not sufficiently accurate for alloys with charge-transfer effects. Further analysis, in terms of basis functions,
densities of states and non-spherically averaged charge densities, indicate the importance ofs- andd-electrons of Pt for the stability of both ordered and disordered Ni-Pt alloys. 相似文献
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The alloy transfer matrix approximation is used to study the uniform dynamic susceptibility of a disordered ferromagnetic chain. This approximation allows for a consistent treatment of diagonal and off-diagonal disorder. The results, in the limit of low concentrations, are in agreement with the exact single impurity ones. Intensities and lineshapes for infrared absorption are calculated for finite impurity concentrations and different values of the relative anisotropy parameter of a model alloy. 相似文献
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The coherent potential approximation is not sufficiently accurate to describe the details of the energy spectrum of a disordered alloy when the mean free path is short. A new approximation based on treating, self-consistently, clusters of sites is introduced. 相似文献
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We apply renormalization group techiques to evaluate the local density of phonon states for the isotopically (randomly) disordered linear chain. The method is based on a systematic decimation of atoms in the chain. Numerical studies reveal a richly structured spectrum, in reasonable agreement both with numerical simulations and with exact moments results. This is the first analytic alloy approximation which takes into account potential fluctuations of arbitrary range. 相似文献