mirror of https://gitlab.com/QEF/q-e.git
78 lines
2.4 KiB
Fortran
78 lines
2.4 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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FUNCTION efermig (et, nbnd, nks, nelec, wk, Degauss, Ngauss, is, isk)
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!--------------------------------------------------------------------
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!
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! Finds the Fermi energy - Gaussian Broadening
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! (see Methfessel and Paxton, PRB 40, 3616 (1989 )
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!
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USE io_global, ONLY : stdout
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USE kinds, ONLY : DP
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USE constants, ONLY: rytoev
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USE mp, ONLY : mp_max, mp_min
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USE mp_global, ONLY : inter_pool_comm
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implicit none
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! I/O variables
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integer, intent(in) :: nks, nbnd, Ngauss, is, isk(nks)
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real(DP), intent(in) :: wk (nks), et (nbnd, nks), Degauss, nelec
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real(DP) :: efermig
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!
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real(DP), parameter :: eps= 1.0d-10
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integer, parameter :: maxiter = 300
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! internal variables
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real(DP) :: Ef, Eup, Elw, sumkup, sumklw, sumkmid
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real(DP), external:: sumkg
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integer :: i, kpoint
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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 mp_max( eup, inter_pool_comm )
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call mp_min( elw, inter_pool_comm )
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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, is, isk)
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sumklw = sumkg (et, nbnd, nks, wk, Degauss, Ngauss, Elw, is, isk)
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if ( (sumkup - nelec) < -eps .or. (sumklw - nelec) > eps ) &
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call errore ('efermig', 'internal error, cannot bracket Ef', 1)
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do i = 1, maxiter
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Ef = (Eup + Elw) / 2.d0
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sumkmid = sumkg (et, nbnd, nks, wk, Degauss, Ngauss, Ef, is, isk)
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if (abs (sumkmid-nelec) < eps) then
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efermig = Ef
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return
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elseif ( (sumkmid-nelec) < -eps) 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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if (is /= 0) WRITE(stdout, '(5x,"Spin Component #",i3)') is
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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 * rytoev, sumkmid
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!
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efermig = Ef
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return
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end FUNCTION efermig
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