mirror of https://gitlab.com/QEF/q-e.git
79 lines
2.4 KiB
Fortran
79 lines
2.4 KiB
Fortran
!
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! Copyright (C) 2001-2010 Quantum ESPRESSO group
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! This file is distributed under the terms of the
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! GNU General Public License. See the file `License'
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! in the root directory of the present distribution,
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! or http://www.gnu.org/copyleft/gpl.txt .
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!
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!----------------------------------------------------------------------------
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SUBROUTINE gk_sort_limit( k, ngm, g, ecut, ngk, igk, gk )
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!----------------------------------------------------------------------------
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!
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! ... sorts k+g in order of increasing magnitude, up to ecut
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! ... NB: this version should yield the same ordering for different ecut
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! ... and the same ordering in all machines AS LONG AS INPUT DATA
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! ... IS EXACTLY THE SAME
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!
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USE kinds, ONLY : DP
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USE constants, ONLY : eps8
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USE wvfct, ONLY : npwx
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!
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IMPLICIT NONE
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!
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REAL(DP), INTENT(in) :: k(3) ! the k point
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INTEGER, INTENT(in) :: ngm ! the number of g vectors
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REAL(DP), INTENT(in) :: g(3,ngm) ! the coordinates of G vectors
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REAL(DP), INTENT(in) :: ecut ! the cut-off energy
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INTEGER, INTENT(out) :: ngk ! the number of k+G vectors inside the "ecut sphere"
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INTEGER, INTENT(out) :: igk(npwx) ! the correspondence k+G <-> G
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REAL(DP), INTENT(out) :: gk(npwx) ! the moduli of k+G
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!
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INTEGER :: ng ! counter on G vectors
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INTEGER :: nk ! counter on k+G vectors
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REAL(DP) :: q ! |k+G|^2
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REAL(DP) :: q2x ! upper bound for |G|
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!
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! ... first we count the number of k+G vectors inside the cut-off sphere
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!
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q2x = ( sqrt( sum(k(:)**2) ) + sqrt( ecut ) )**2
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!
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ngk = 0
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igk(:) = 0
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gk (:) = 0.0_dp
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!
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DO ng = 1, ngm
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q = sum( ( k(:) + g(:,ng) )**2 )
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IF(q<=eps8) q=0.d0
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!
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! ... here if |k+G|^2 <= Ecut
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!
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IF ( q <= ecut ) THEN
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IF ( ngk+1 > npwx ) exit
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ngk = ngk + 1
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!
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gk(ngk) = q
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!
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! set the initial value of index array
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igk(ngk) = ng
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ELSE
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! if |G| > |k| + SQRT( Ecut ) stop search and order vectors
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IF ( sum( g(:,ng)**2 ) > ( q2x + eps8 ) ) exit
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ENDIF
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ENDDO
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!
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IF ( ng > ngm ) &
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CALL infomsg( 'gk_sort', 'unexpected exit from do-loop')
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!
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! ... order vector gk keeping initial position in index
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!
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CALL hpsort_eps( ngk, gk, igk, eps8 )
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!
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! ... now order true |k+G|
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!
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DO nk = 1, ngk
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gk(nk) = sum( (k(:) + g(:,igk(nk)) )**2 )
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ENDDO
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!
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END SUBROUTINE gk_sort_limit
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