Band decomposed charge densities of any K point

[sgyang345]

Background

At present, it seems that ABACUS can only calculate the partial (band decomposed) charge density for $\Gamma$ point according to parameter calculation = get_pchg.

Describe the solution you'd like

It is suggested to increase the function for band decomposed charge densities of any K point.

Additional Context

In addition, I hope to get some help from the developers on how to calculate the partial charge density when the atomic orbitals and coefficients are obtained.

I 'm developing post-processing functionality for DeepH programs, but I need some help in theory and technology, and I 'll be grateful !

[hongriTianqi]

@sgyang345 The Chapter 15 "Localized orbitals: full calculations" in the book of Electronic Structure: Basic Theory and Practical Methods of Richard M. Martin is suggested.

[sgyang345]

Thank you very much for your help!

The biggest difficulty I face is how to get the charge density in real space for LCAO.
As far as I know, a Fourier transform from reciprocal space to real space is needed, and I have no clue about this part.
Could you please provide me some suggestions?

Thanks a lot!

[hongriTianqi]

@sgyang345 Fourier transform related codes are put in the module_basis/module_pw, maybe you can run the unit tests inside that module to find some clues.

[hongriTianqi]

@sgyang345 ABACUS's reference might also help:

Pengfei Li, et al. “Large-scale ab initio simulations based on systematically improvable atomic basis.” Computational Materials Science 112 (2016): 503-517. 

[hongriTianqi]

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