[Pw_forum] indexing of G and k+G vectors.

Stefano de Gironcoli degironc at sissa.it
Mon Apr 14 17:38:41 CEST 2003

Dear user,

the list of G vectors g(3,ngm) contains all plane wave with kinetic energy
below ecutrho in order of increasing length.

The index igk(npw) created by calling
gk_sort (xk (1, ik), ngm, g, ecutwfc / tpiba2, npw, igk, g2kin)
for each kpoint when needed (or reading from the file  'prefix'.igk, 
contains the information in order to go from the ordering of increasing  
length (the one used for eigenvectors) to the ordering od increasing G 
(used for charge density, potential etc).

That is:  k+G(igk(i)) is the vector that comes in the i-th place in the 
list of k+G
ordered by their length

g2kin(i) is the corresponding kinetic energy in unit of tpiba2 

best regards,

   Stefano de Gironcoli

Raghani Pushpa wrote:

>Dear user,
>There is variable in the code called 'npwx'. I thought it is the number of 
>plane waves i.e. the no of G vectors. However, there is a difference of 
>factor of 8 between them, i.e. no of G vectors ~ 8*npwx. What does this 
>variable physically mean? 
>How can I get the coefficients C(k+G) from the code and how will I get the 
>correspondence between C(k+G) and G vectors i.e. which C(k+G) corresponds 
>to which G vector?

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