[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,
unit=iunigk)
contains the information in order to go from the ordering of increasing
k+G
length (the one used for eigenvectors) to the ordering od increasing G
length
(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
[=(2pi/alat)^2]
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?
>
>Thanx,
>Pushpa
>
>
>
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