!-----------------------------------------------------------------------
  ! Copyright (C) 2010-2015 Henry Lambert, Feliciano Giustino
  ! 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 .
  !-----------------------------------------------------------------------
!
! Copyright (C) 2001-2004 PWSCF 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 openfilq()
!----------------------------------------------------------------------------
! ... This subroutine opens all the files necessary for the GW q
! ... calculation.
 
  USE kinds,          ONLY : DP
  USE control_flags,  ONLY : io_level, modenum
  USE units_gw,       ONLY : iuwfc, iudwf, iubar, iucom, iudvkb3, &
                             iudrhous, iuebar, iudrho, iudyn, iudvscf, &
                             lrwfc, lrdwf, lrbar, lrcom, lrdvkb3, lrcoul, &
                             lrdrhous, lrebar, lrdrho, iudwfm, iudwfp, iuncoul, lrgrn, iungreen
  USE io_files,       ONLY : tmp_dir, diropn, seqopn, wfc_dir
  USE freq_gw,        ONLY : nfs, nwgreen
  USE control_gw,     ONLY : ext_recover, trans, tmp_dir_gw, lgamma, do_coulomb
  USE save_gw,        ONLY : tmp_dir_save
  USE qpoint,         ONLY : nksq
  USE output,         ONLY : fildyn, fildvscf
  USE wvfct,          ONLY : nbnd, npwx
  USE fft_base,       ONLY : dfftp, dffts
  USE lsda_mod,         ONLY : nspin
  USE uspp,             ONLY : nkb, okvan
  USE io_files,         ONLY : prefix, iunigk
  USE noncollin_module, ONLY : npol, nspin_mag
  USE control_flags,    ONLY : twfcollect, io_level
  USE mp_global,        ONLY : me_pool
  USE io_global,        ONLY : ionode
  USE buffers,          ONLY : open_buffer
  USE input_parameters, ONLY : nk1, nk2, nk3
  USE mp_world,      ONLY : nproc, mpime
  !
  IMPLICIT NONE
  !
  INTEGER :: ios
  ! integer variable for I/O control
  CHARACTER (len=256) :: filint
  ! the name of the file
  LOGICAL :: exst, exst_mem
  ! logical variable to check file existe
  !
  REAL(DP) :: edum(1,1), wdum(1,1)
  INTEGER :: ndr, ierr
  !
  !
  IF (LEN_TRIM(prefix) == 0) CALL errore ('openfilq', 'wrong prefix', 1)
  !     There are six direct access files to be opened in the tmp area
  !     The file with the wavefunctions. In the lgamma case reads those
  !     written by pw.x. In the other cases those calculated by gw.x
  tmp_dir=tmp_dir_gw
  IF (lgamma) tmp_dir=tmp_dir_save
  iuwfc = 20
  lrwfc = nbnd * npwx * npol


  CALL open_buffer (iuwfc, 'wfc', lrwfc, io_level, exst_mem, exst, tmp_dir_gw)
  IF (.NOT.exst.AND..NOT.exst_mem) THEN
     CALL errore ('openfilq', 'file '//trim(prefix)//'.wfc not found', 1)
  END IF
  !
  ! From now on all files are written with the _gw prefix
  !
  tmp_dir=tmp_dir_gw
  !
  !    The file with deltaV_{bare} * psi
  !
  if(do_coulomb) then
    iubar = 21
    lrbar = nbnd * npwx * npol
    CALL open_buffer (iubar, 'bar', lrbar, io_level, exst_mem, exst, tmp_dir)
    IF (ext_recover.AND..NOT.exst) &
       CALL errore ('openfilq','file '//trim(prefix)//'.bar not found', 1)
  !
  !    The file with the solution delta psi
  !
    iudwf = 22
    lrdwf =  nbnd * npwx * npol
    CALL open_buffer (iudwf, 'dwf', lrdwf, io_level, exst_mem, exst, tmp_dir)
    IF (ext_recover.AND..NOT.exst) &
    CALL errore ('openfilq','file '//trim(prefix)//'.dwf not found', 1)

    iudwfm = 29 
    iudwfp = 30
    CALL open_buffer (iudwfp, 'dwfp', lrwfc, io_level, exst_mem, exst, tmp_dir)
    CALL open_buffer (iudwfm, 'dwfm', lrwfc, io_level, exst_mem, exst, tmp_dir)
  endif
  !
  !   open a file with the static change of the charge
  !
    IF (okvan) THEN
     iudrhous = 25
     lrdrhous =  dfftp%nnr * nspin_mag
     CALL open_buffer (iudrhous, 'prd', lrdrhous, io_level, exst_mem, exst,tmp_dir)
     IF (ext_recover.AND..NOT.exst) &
        CALL errore ('openfilq','file '//trim(prefix)//'.prd not found', 1)
  ENDIF
  !
  !  Optional file(s) containing Delta\rho (opened and written in solve_e
  !  and solve_linter). Used for third-order calculations.
  !
  iudrho = 23
  lrdrho = 2 * dfftp%nr1x * dfftp%nr2x * dfftp%nr3x * nspin_mag
  !   Here the sequential files
  !   The igk at a given k (and k+q if q!=0)
  !
  IF (nksq > 1) CALL seqopn (iunigk, 'igk', 'unformatted', exst)

!HL write files for \Delta\psi^{\pm}
  RETURN
END SUBROUTINE openfilq