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!
! Copyright (C) 2001-2016 Quantum ESPRESSO group
! This file is distributed under the terms of the
! GNU General Public License. See the file `License'
! in the root directory of the present distribution,
! or http://www.gnu.org/copyleft/gpl.txt .
!
!-----------------------------------------------------------------------
SUBROUTINE setup_nbnd_occ
!-----------------------------------------------------------------------
!
! This subroutine computes the number of occupied bands for each k point
!
USE kinds, ONLY : DP
USE constants, ONLY : degspin, pi
USE klist, ONLY : xk, ltetra, lgauss, degauss, ngauss, nks, &
nelec, nelup, neldw, two_fermi_energies, wk
USE ener, ONLY : ef
USE wvfct, ONLY : nbnd, et
USE control_lr, ONLY : nbnd_occ
USE io_global, ONLY : stdout
USE noncollin_module, ONLY : noncolin
USE lsda_mod, ONLY : lsda, isk
USE ktetra, ONLY : tetra_type
!
IMPLICIT NONE
!
REAL(DP) :: target, small, fac, xmax
! auxiliary variables used
! to set nbnd_occ in the metallic case
INTEGER :: ik, ibnd, ipol
!
CALL start_clock ('setup_nbnd_occ')
!
ALLOCATE ( nbnd_occ(nks) )
nbnd_occ(:) = 0
IF (lgauss) THEN
!
! Discard conduction bands such that w0gauss(x,n) < small
!
! hint:
! small = 1.0333492677046d-2 ! corresponds to 2 gaussian sigma
! small = 6.9626525973374d-5 ! corresponds to 3 gaussian sigma
! small = 6.3491173359333d-8 ! corresponds to 4 gaussian sigma
!
small = 6.9626525973374d-5
!
! - appropriate limit for gaussian broadening (used for all ngauss)
!
xmax = sqrt ( - log (sqrt (pi) * small) )
!
! - appropriate limit for Fermi-Dirac
!
IF (ngauss.eq. - 99) THEN
fac = 1.d0 / sqrt (small)
xmax = 2.d0 * log (0.5d0 * (fac + sqrt (fac * fac - 4.d0) ) )
ENDIF
!
target = ef + xmax * degauss
!
DO ik = 1, nks
DO ibnd = 1, nbnd
IF (et(ibnd, ik) .lt.target) nbnd_occ(ik) = ibnd
ENDDO
IF (nbnd_occ(ik) .eq. nbnd) WRITE( stdout, '(5x,/,&
&"Possibly too few bands at point ", i4,3f10.5)') &
ik, (xk (ipol, ik) , ipol = 1, 3)
ENDDO
!
ELSE IF (ltetra) THEN
IF (tetra_type /= 1 .and. tetra_type /= 2) CALL errore &
('setup_nbnd_occ','Optimized or linear tetrahedra only', 1)
ELSE
!
IF (noncolin) THEN
nbnd_occ = nint (nelec)
ELSE
IF ( two_fermi_energies ) THEN
DO ik = 1, nks
IF (isk(ik)==1) THEN
nbnd_occ (ik) = nint (nelup)
ELSE
nbnd_occ (ik) = nint (neldw)
ENDIF
ENDDO
ELSE
IF (lsda) CALL infomsg('setup_nbnd_occ', &
'Occupation numbers probably wrong')
DO ik = 1, nks
nbnd_occ (ik) = nint (nelec) / degspin
ENDDO
ENDIF
ENDIF
!
ENDIF
!
CALL stop_clock ('setup_nbnd_occ')
!
RETURN
!
END SUBROUTINE setup_nbnd_occ
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