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enola

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[交流] 【转帖】半芯太电子 Semi-Core electron 已有5人参与

半芯太电子。。。
When we build a pseudopotential (psp), we froze the inner core states and
treat only the valence electrons due to the fact that the properties of
materials are largely determined by the outer-layer valence electrons. In
order to obtain a psp with good transferability, there should be very small
overlap between core and valence electron distributions which is true for most
light elements. For most the elements, the overlap between core and valence
electron can be so large that the psp built in the usual way cannot lead to
the correct properties of materials composed of that element (e.g., Na, K).
There are two methods to solve the above problem. 1) Nonlinear core
correction, we use an artificial core charge distribution to replace the real
core charge distribution. When building psp, we substract the contribution to
Vxc and VHartree, which comes from the artificial core, and when using the
psp, add the corresponding ones (see PRB 26, 1378). When doing nonlinear core
correction, we don't increase the number of valence electrons but only
increase the cutoff energy for plane-wave calculations due to the added core.
2) Semicore states, which means including some states that you usually treat
as core states when you build a pseudopotential. For example, when building a
psp for Ca, we not only include 4s, 4p, 3d but also include 3s, 3p in the
valence states. For this method, we include a lot more electrons (e.g. 8 more
e/atom for Ca), and also need a much large cutoff energy because we have
included much more localized 3s, 3p electrons. So including semicore states
will result in much harder calculations.

In fact, for most cases, nonlinear core correction is already enough for a
good psp and including semicore states is kind of overkill. So my suggestion
is: use the nonlinear core correction when you need it, use semicore states
unless you have to.

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timeflies..

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xianggui7895

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不错，学习了

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2楼2011-01-09 17:20:42

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zhangguangping

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gzqdyouxia(金币+1):鼓励交流 2011-01-09 21:55:22

引用回帖:

Originally posted by enola at 2011-01-09 08:29:16:
半芯太电子。。。
When we build a pseudopotential (psp), we froze the inner core states and
treat only the valence electrons due to the fact that the properties of
materials are largely determ ...

不错，学写了。顺便问一句：“need a much large cutoff energy”中的cutoff energy是指的什么呢？是平面波基矢里面的一个量吧？如果是原子轨道基矢的话，如siesta对应的量是不是就是MeshCutoff呢？决定了数值计算中格点的密度。谢谢！

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弘德明志博学笃行

3楼2011-01-09 20:39:34

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enola

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引用回帖:

Originally posted by zhangguangping at 2011-01-09 20:39:34:

不错，学写了。顺便问一句：“need a much large cutoff energy”中的cutoff energy是指的什么呢？是平面波基矢里面的一个量吧？如果是原子轨道基矢的话，如siesta对应的量是不是就是MeshCutoff呢？决定了数值计 ...

cutoff energy 就是就起方程展开时的基组大小。
Siesta不是很熟悉啊。。。

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timeflies..

4楼2011-01-10 08:56:01

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