mirror of https://gitlab.com/QEF/q-e.git
94 lines
3.0 KiB
Fortran
94 lines
3.0 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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!-----------------------------------------------------------------------
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subroutine sgam_ph (at, bg, nsym, s, irt, tau, rtau, nat, sym)
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!-----------------------------------------------------------------------
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!
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! This routine computes the vector rtau which contains for each
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! atom and each rotation the vector S\tau_a - \tau_b, where
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! b is the rotated a atom, given by the array irt. These rtau are
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! non zero only if fractional translations are present.
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!
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! revised layout 2 may 1995 by Andrea Dal Corso
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!
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#include "f_defs.h"
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USE kinds
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implicit none
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!
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! first the dummy variables
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!
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integer :: nsym, s (3, 3, 48), nat, irt (48, nat)
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! input: symmetries of the point grou
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! input: symmetry matrices
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! input: number of atoms in the unit
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! input: for each atom gives the rota
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real(DP) :: at (3, 3), bg (3, 3), tau (3, nat), rtau (3, 48, nat)
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! input: direct lattice vectors
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! input: reciprocal lattice vectors
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! input: coordinates of the atoms
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! output: the direct translations
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logical :: sym (nsym)
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! input: if true the symmetry exists
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!
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! here the local variables
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!
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integer :: na, isym, nb, ipol
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! counter on atoms
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! counter on symmetry operations
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! buffer for atom
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! counter on polarization
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real(DP) , allocatable :: xau (:,:), rau (:,:)
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real(DP) :: ft (3)
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! atomic coordinates in crystal axis
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! rotated atomic coordinates
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! fractionary translation
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allocate (xau(3,nat))
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allocate (rau(3,nat))
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!
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! compute the atomic coordinates in crystal axis
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!
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do na = 1, nat
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do ipol = 1, 3
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! crystal coordinates
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xau (ipol, na) = bg (1, ipol) * tau (1, na) + bg (2, ipol) &
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* tau (2, na) + bg (3, ipol) * tau (3, na)
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! of the current atom
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enddo
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enddo
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!
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! for each symmetry operation
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!
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do isym = 1, nsym
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if (sym (isym) ) then
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do na = 1, nat
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nb = irt (isym, na)
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do ipol = 1, 3
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ft (ipol) = s (1, ipol, isym) * xau (1, na) + s (2, ipol, isym) &
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* xau (2, na) + s (3, ipol, isym) * xau (3, na) - xau (ipol, nb)
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enddo
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do ipol = 1, 3
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rtau (ipol, isym, na) = at (ipol, 1) * ft (1) + at (ipol, 2) &
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* ft (2) + at (ipol, 3) * ft (3)
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enddo
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enddo
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endif
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enddo
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!
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! deallocate workspace
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!
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deallocate(rau)
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deallocate(xau)
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return
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end subroutine sgam_ph
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