[QE-users] npw vs npwx

[Paolo Giannozzi]

On Wed, Nov 11, 2020 at 7:29 PM Andrew Xu <andrewaccount at gmail.com> wrote:

I'm confused why npw and npwx is used, instead of only npw or only npwx
>

npw = actual number of plane waves
npwx= physical dimension of arrays containing plane-wave components

The reason for the difference is that different k-points have different
values of npw, so npwx is set to the maximum value of npw across k-points.
Once upon a time, npwx was used to increase efficiency: setting it to an
odd number, for obscure reasons related to memory access and memory banks,
allowed to speed up some calculations, but I don't think this is done any
longer.

Paolo

. Is this saying the number of columns of op(wfc) (which is the number of
> rows of swfc) is npwx, but we only use the first npw columns of op(wfc)
> (rows of swfc) because the entries in the last npwx - npw columns of
> op(wfc) (rows of swfc) are all zero?
>
> Best regards,
> Andrew
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-- 
Paolo Giannozzi, Dip. Scienze Matematiche Informatiche e Fisiche,
Univ. Udine, via delle Scienze 208, 33100 Udine, Italy
Phone +39-0432-558216, fax +39-0432-558222
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