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redskywei

木虫 (著名写手)

应助: 14 (小学生)
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[交流] 【求助】castep中光学性能吸收反射谱的单位是什么？

请问，castep中计算光学性能的吸收谱中，单位是什么？
他的帮助里没找到相关的说明，另外，这个吸收系数为什么这么高？我算的碳管吸收有的峰值30000这么多。请高人给俺解惑一下。
反射系数的话就是简单的强度反射率了吧，可以认为是没有单位么？这个参量中峰值最大的才0.04. 不知道这么理解对否。

这里现行谢过。

我在帮助里仔细又找了一下，找到了相关公式，可是里面的量的说明还是不能让我得出吸收系数的单位是啥。我在5.0的Optical properties->Definition of optical constants下看到了公式，内容如下（公式不知道怎么能搞上了，呵呵）：CASTEP can calculate the optical properties of solids that are due to electronic transitions.

In general, the difference in the propagation of an electromagnetic wave through vacuum and some other material can be described by a complex refractive index, N:

Eq. CASTEP 48

In vacuum N is real, and equal to unity. For transparent materials it is purely real, the imaginary part being related to the absorption coefficient by:

Eq. CASTEP 49

The absorption coefficient indicates the fraction of energy lost by the wave when it passes through the material, so that the intensity at the distance x from the surface is I(x)=I(0)exp(-2πηx), where I(0) is the intensity of the incident light.

The reflection coefficient can be obtained for the simple case of normal incidence onto a plane surface by matching both the electric and magnetic fields at the surface:

Eq. CASTEP 50

However, when performing calculations of optical properties it is common to evaluate the complex dielectric constant and then express other properties in terms of it. The complex dielectric constant, ε(ω), is given by:

Eq. CASTEP 51

and hence the relation between the real and imaginary parts of the refractive index and dielectric constant is:

Eq. CASTEP 52

Another frequently used quantity for expressing optical properties is the optical conductivity, σ(ω):

Eq. CASTEP 53

Optical conductivity is usually used to characterize metals, however CASTEP is aimed more toward the optical properties of insulators and semiconductors. The main difference between the two is that intraband transitions play important role in the IR part of the optical spectra of metals and these transitions are not considered at all in CASTEP.

A further property that can be calculated from the complex dielectric constant is the energy loss function. It describes the energy lost by an electron passing through a homogeneous dielectric material and is given by:

Eq. CASTEP 54

还请高人不吝赐教～～～

[ Last edited by redskywei on 2010-11-29 at 20:28 ]

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