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! Copyright (C) 2002-2005 J. K. Dewhurst, S. Sharma and C. Ambrosch-Draxl.
! This file is distributed under the terms of the GNU General Public License.
! See the file COPYING for license details.
!BOP
! !ROUTINE: olpistl
! !INTERFACE:
pure subroutine olpistl(ngp,igpig,ld,o)
! !USES:
use modmain
! !INPUT/OUTPUT PARAMETERS:
! ngp : number of G+p-vectors (in,integer)
! igpig : index from G+p-vectors to G-vectors (in,integer(ngkmax))
! ld : leading dimension of o (in,integer)
! o : overlap matrix (inout,complex(*))
! !DESCRIPTION:
! Computes the interstitial contribution to the overlap matrix for the APW
! basis functions. The overlap is given by
! $$ O^{\rm I}({\bf G+k,G'+k})=\tilde{\Theta}({\bf G-G'}), $$
! where $\tilde{\Theta}$ is the characteristic function. See routine
! {\tt gencfun}.
!
! !REVISION HISTORY:
! Created April 2003 (JKD)
!EOP
!BOC
implicit none
! arguments
integer, intent(in) :: ngp,igpig(ngkmax),ld
complex(8), intent(out) :: o(ld,*)
! local variables
integer ig,j1,j2,j3,i,j
do j=1,ngp
ig=igpig(j)
j1=ivg(1,ig); j2=ivg(2,ig); j3=ivg(3,ig)
do i=1,j
ig=igpig(i)
ig=ivgig(ivg(1,ig)-j1,ivg(2,ig)-j2,ivg(3,ig)-j3)
o(i,j)=cfunig(ig)
end do
end do
end subroutine
!EOC
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