mirror of https://gitlab.com/QEF/q-e.git
64 lines
1.9 KiB
Fortran
64 lines
1.9 KiB
Fortran
!
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! Copyright (C) 2001-2003 PWSCF 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 efermig (et, nbnd, nks, nelec, wk, Degauss, Ngauss, Ef)
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!--------------------------------------------------------------------
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!
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! Finds the Fermi energy - Gaussian Broadening (Methfessel-Paxton)
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!
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USE io_global, ONLY : stdout
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USE kinds
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implicit none
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integer :: nks, nbnd, i, kpoint, Ngauss
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real(kind=DP) :: wk (nks), et (nbnd, nks), Degauss, Ef, Eup, Elw, &
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sumkup, sumklw, sumkmid, nelec
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real(kind=DP), external:: sumkg
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!
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! find bounds for the Fermi energy. Very safe choice!
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!
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Elw = et (1, 1)
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Eup = et (nbnd, 1)
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do kpoint = 2, nks
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Elw = min (Elw, et (1, kpoint) )
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Eup = max (Eup, et (nbnd, kpoint) )
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enddo
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Eup = Eup + 2 * Degauss
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Elw = Elw - 2 * Degauss
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#ifdef __PARA
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!
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! find min and max across pools
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!
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call poolextreme (Eup, + 1)
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call poolextreme (Elw, - 1)
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#endif
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!
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! Bisection method
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!
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sumkup = sumkg (et, nbnd, nks, wk, Degauss, Ngauss, Eup)
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sumklw = sumkg (et, nbnd, nks, wk, Degauss, Ngauss, Elw)
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if ( (sumkup - nelec) .lt. - 1.0e-10.or. (sumklw - nelec) &
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.gt.1.0e-10) call errore ('Efermi', 'unexpected error', 1)
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do i = 1, 50
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Ef = (Eup + Elw) / 2.0
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sumkmid = sumkg (et, nbnd, nks, wk, Degauss, Ngauss, Ef)
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if (abs (sumkmid-nelec) .lt.1.0e-10) then
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return
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elseif ( (sumkmid-nelec) .lt. - 1.0e-10) then
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Elw = Ef
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else
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Eup = Ef
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endif
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enddo
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WRITE( stdout, '(5x,"Warning: too many iterations in bisection"/ &
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& 5x,"Ef = ",f10.6," sumk = ",f10.6," electrons")' ) &
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Ef * 13.6058, sumkmid
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!
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return
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end subroutine efermig
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