Paramagnetic Ni Cu Alloys: Electronic Density of States in the Coherent-Potential Approximation
Paramagnetic Ni Cu Alloys: Electronic Density of States in the Coherent-Potential Approximation
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顺磁镍铜合金：相干势近似中的电子态密度
DOI：
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发表时间：
1970
期刊：
影响因子：
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通讯作者：
H. Ehrenreich
中科院分区：
文献类型：
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作者：
S. Kirkpatrick;B. Velicky;H. Ehrenreich
相干势近似（CPA）被扩展到研究一般能带形状和具有轨道简并的系统。这使得它能够应用于现实系统，特别是 $mathrm{Ni}mathrm{Cu}$ 合金。详细考虑了合金化对面心立方过渡金属中状态密度的一些特征的高度不对称模型状态密度的影响。使用正交平面波和紧束缚 $d$ 函数的基础构建顺磁 $mathrm{Ni}mathrm{Cu}$ 模型哈密顿量。轨道简并和杂化被视为顺磁镍。假设合金化的影响仅限于 $densuremath{-}d$ 块的对角元素。该模型适用于富镍合金，用于获得完整 CPA 方程的简单解的近似也是如此。结果与最近的 $mathrm{Ni}mathrm{Cu}$ 光电发射数据以及 Lang 和 Ehrenreich 使用的“最小极性”假设一致。它们与刚性带模型不兼容，因为随机合金的散射势与峰宽度相比很强。计算出的浓度依赖性表明，主峰在改变幅度和形状时保持静止，而不是状态密度的严格变化。将总态密度分解为 Ni 和 Cu 贡献证实，对于费米能级的预期位置，$d$ 空穴主要位于 Ni 位点上。
The coherent-potential approximation (CPA) is extended to study general band shapes and systems having orbital degeneracy. This permits its application to realistic systems, in particular the $mathrm{Ni}mathrm{Cu}$ alloys. The effects of alloying on a highly asymmetric model density of states characteristic of some of the features of the density of states in fcc transition metals are considered in detail. A model Hamiltonian for paramagnetic $mathrm{Ni}mathrm{Cu}$ is constructed using a basis of orthogonalized plane waves and tight-binding $d$ functions. Orbital degeneracy and hybridization are treated as in paramagnetic Ni. Effects of alloying are assumed to be restricted to the diagonal elemensts of the $densuremath{-}d$ block. The model is applicable to the Ni-rich alloys, as is the approximation used to obtain simple solutions of the full CPA equations. The results are consistent with recent photoemission data on $mathrm{Ni}mathrm{Cu}$, and with the "minimum polarity" hypothesis used by Lang and Ehrenreich. They are incompatible with the rigid-band model because the scattering potential of the random alloy is strong compared to the peak widths. Rather than a rigid shift of the density of states, the calculated concentration dependence shows that the main peaks remain stationary while changing magnitude and shape. Decomposition of the total density of states into Ni and Cu contributions confirms that, for the expected position of the Fermi level, the $d$ holes are located primarily on Ni sites.