[Pw_forum] what is the meaning of 'ngw' and 'igwx' in the output file of pw_export.x

[Chong Wang]

Hello,


I need access to electron wave functions, so I am using pw_export.x. However, I am confused by 'ngw' and 'igwx' in the output xml file.


This is my understanding:


1. 'Wfc_grids' - 'Kpoint.1' - 'grid' contains all Fourier base functions. For example, the first one is '0 0 0', which means the first Fourier base function is exp(i*(0*g1+0*g2+0*g3)).


2. 'Eigenvectors' - 'Kpoint.1' - 'Wfc.1' contains all Fourier coefficients of the wave function of the first band of the first k point. For example, if the first number is '-2.760388199287167E-002,-6.506816021159129E-001', the corresponding coefficient is -2.760388199287167E-002+i*-6.506816021159129E-001


3.  'igwx' tag in 'Eigenvectors' - 'Kpoint.1' - 'info' is the number of Fourier base functions.


What bothers me is that there is another number 'ngwx' which is different from 'igwx'. Also 'Wfc-grids' - 'Kpoint.1' - 'index' has 'igwx' numbers but the last number is 'ngwx'.


I want to know what's the meaning of 'ngwx' and 'igwx' so that I can make sure I correctly read the wave functions.


Best!


Chong Wang

Ph.D. Candidate

Institute of Advanced Study, Tsinghua University, 100084, Beijing
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