mirror of https://gitlab.com/QEF/q-e.git
84 lines
2.3 KiB
Fortran
84 lines
2.3 KiB
Fortran
!
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! Copyright (C) 2001 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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MODULE sym_def_module
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CONTAINS
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subroutine sym_def (def, irr)
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!---------------------------------------------------------------------
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!! Symmetrizes the first order changes of the Fermi energies of an
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!! irreducible representation. These objects are defined complex because
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!! perturbations may be complex.
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!
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!! Used in the q=0 metallic case only.
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!
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USE kinds, only : DP
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USE modes, ONLY : npert, t, tmq
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USE control_ph, ONLY : lgamma_gamma
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USE lr_symm_base, ONLY : minus_q, nsymq
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implicit none
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integer :: irr
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!! input: the representation under consideration
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complex(DP) :: def(3)
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!! inp/out: the fermi energy changes.
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!! NB: def(3) should be def(npertx), but it is used only at Gamma
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!! where the dimension of irreps never exceeds 3.
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!
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! ... local variables
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!
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integer :: ipert, jpert, isym, irot
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! counter on perturbations
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! counter on perturbations
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! counter on symmetries
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! the rotation
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complex(DP) :: w_def(3)
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! the fermi energy changes (work array)
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IF (lgamma_gamma) RETURN
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if (nsymq == 1 .and. (.not.minus_q) ) return
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if (npert(irr) > 3) CALL errore("sym_def", "npert(irr) exceeds 3", 1)
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!
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! first the symmetrization S(irotmq)*q = -q + Gi if necessary
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!
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if (minus_q) then
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w_def = (0.d0, 0.d0)
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do ipert = 1, npert (irr)
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do jpert = 1, npert (irr)
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w_def (ipert) = w_def (ipert) + tmq (jpert, ipert, irr) &
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* def (jpert)
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enddo
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enddo
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do ipert = 1, npert (irr)
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def (ipert) = 0.5d0 * (def (ipert) + CONJG(w_def (ipert) ) )
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enddo
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endif
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!
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! Here we symmetrize with respect to the small group of q
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!
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w_def = (0.d0, 0.d0)
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do ipert = 1, npert (irr)
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do isym = 1, nsymq
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irot = isym
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do jpert = 1, npert (irr)
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w_def (ipert) = w_def (ipert) + t (jpert, ipert, irot, irr) &
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* def (jpert)
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enddo
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enddo
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enddo
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!
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! normalize and exit
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!
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def = w_def / DBLE(nsymq)
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return
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end subroutine sym_def
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END MODULE sym_def_module
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