mirror of https://gitlab.com/QEF/q-e.git
79 lines
2.5 KiB
Fortran
79 lines
2.5 KiB
Fortran
!
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! Copyright (C) 2001-2008 Quantum ESPRESSO 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 sgam_ph_new (at, bg, nsym, s, irt, tau, rtau, nat)
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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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USE kinds, ONLY : DP
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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, intent(in) :: nsym, s (3, 3, 48), nat, irt (48, nat)
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! nsym: number of symmetries of the point group
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! s: matrices of symmetry operations
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! nat : number of atoms in the unit cell
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! irt(n,m) = transformed of atom m for symmetry n
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real(DP), intent(in) :: at (3, 3), bg (3, 3), tau (3, nat)
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! at: direct lattice vectors
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! bg: reciprocal lattice vectors
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! tau: coordinates of the atoms
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real(DP), intent(out):: rtau (3, 48, nat)
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! rtau: the direct translations
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!
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! here the local variables
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!
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integer :: na, nb, isym, ipol
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! counters on: atoms, symmetry operations, polarization
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real(DP) , allocatable :: xau (:,:)
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real(DP) :: ft (3)
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!
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allocate (xau(3,nat))
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!
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! compute the atomic coordinates in crystal axis, xau
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!
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do na = 1, nat
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do ipol = 1, 3
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xau (ipol, na) = bg (1, ipol) * tau (1, na) + &
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bg (2, ipol) * tau (2, na) + &
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bg (3, ipol) * tau (3, na)
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enddo
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enddo
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!
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! for each symmetry operation, compute the atomic coordinates
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! of the rotated atom, ft, and calculate rtau = Stau'-tau
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!
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rtau(:,:,:) = 0.0_dp
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do isym = 1, nsym
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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) + &
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s (2, ipol, isym) * xau (2, na) + &
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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) + &
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at (ipol, 2) * ft (2) + &
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at (ipol, 3) * ft (3)
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enddo
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enddo
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enddo
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!
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! deallocate workspace
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!
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deallocate(xau)
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return
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end subroutine sgam_ph_new
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!
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