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标题: VASP的那个Band Decomposed Charge Density到底是个什么概念？是如何定义的？ [打印本页]

作者
Author: xexlalalan 时间: 2020-10-12 00:03
标题: VASP的那个Band Decomposed Charge Density到底是个什么概念？是如何定义的？
看到有很多文献用VASP计算了一些材料CBM和VBM的charge density/ Partial charge density/ Band decomposed charge density (VASP manual里是这么称呼的)，请问这个东西到底是怎么定义的？感觉这个概念有些奇怪，为什么电子密度这个东西会随不同的band而变化呢？或者这个charge density实质上只是晶体轨道的某种等值面图？

作者
Author: xexlalalan 时间: 2020-10-12 00:12
本帖最后由 xexlalalan 于 2020-10-12 00:16 编辑

补一下VASP manual 原文（2016版，114页）：6.66 Band decomposed chargedensity (parameters)
VASP can calculate the partial (band decomposed) charge density according to parameters specifified in the fifile INCAR. It [size=9.96264pt]must be noted, that the densities calculated by VASP (including the band decomposed charge density) are always symmetrized [size=9.96264pt]using the space group and point group symmetry determined by VASP. In some cases (calculation of charge from selected [size=9.96264pt]k-points) this can lead to undesired results for the band decomposed charge density. In this case, the symmetry needs to be [size=9.96264pt]switched off for the groundstate and successive band decomposed charge density calculations.
Mind that the partial charge density can be calculated only if a preconverged WAVECAR fifile exists, VASP enters the [size=9.96264pt]evaluation routine very quickly and stops immediately after evaluating the partial charge density. This implementation was [size=9.96264pt]chosen to allow a fast (almost interactive) recalculation of the charge density for particular bands and kpoints.[size=13.2835px]

[size=13.2835px]图片写错了，上传的是VBM

作者
Author: 卡开发发 时间: 2020-10-12 19:23

xexlalalan 发表于 2020-10-12 00:12
补一下VASP manual 原文（2016版，114页）：6.66 Band decomposed chargedensity (parameters)
VASP c ...

晶体的轨道和能带编号n和Bloch波矢k都有关，即ψ_nk(r)，band decomposed charge density如果限定了n和k就是ψ_nk(r)的模平方，和n、k还是有关的量。

作者
Author: granvia 时间: 2020-10-12 23:41

卡开发发发表于 2020-10-12 19:23
晶体的轨道和能带编号n和Bloch波矢k都有关，即ψ_nk(r)，band decomposed charge density如果限定了n和k ...

如果是模平方为什么还与波矢k有关？因为Bloch波的k都在exp(i k.r)项里了吧，模平方这一项不是消失了么？

作者
Author: 卡开发发 时间: 2020-10-13 00:16

granvia 发表于 2020-10-12 23:41
如果是模平方为什么还与波矢k有关？因为Bloch波的k都在exp(i k.r)项里了吧，模平方这一项不是消失了么？

轨道系数也是k的函数。直接从上图来看也知道不会是波函数，波函数绘制有相位正负。

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