mirror of https://gitlab.com/QEF/q-e.git
118 lines
3.7 KiB
Fortran
118 lines
3.7 KiB
Fortran
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!
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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 mode_group &
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(modenum, xq, at, bg, nat, nrot, s, irt, minus_q, rtau, sym)
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!-----------------------------------------------------------------------
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!
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! This routine selects, among the symmetry matrices of the point group
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! of a crystal, the symmetry operations which leave a given mode unchanged
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! For the moment it assumes that the mode modenum displaces the atom
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! modenum/3 in the direction mod(modenum,3)+1
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!
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USE kinds, ONLY : DP
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USE constants, ONLY : tpi
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implicit none
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integer, intent(in) :: nat, s (3, 3, 48), irt (48, nat), nrot, modenum
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! nat : the number of atoms of the system
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! s : the symmetry matrices
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! irt : the rotated atom
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! nrot: number of symmetry operations
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! modenum: which displacement pattern
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real(DP), intent(in) :: xq (3), rtau (3, 48, nat), bg (3, 3), at (3, 3)
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! xq : the q point
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! rtau: the translations of each atom
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! bg : the reciprocal lattice vectors
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! at : the direct lattice vectors
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logical, intent(in) :: minus_q
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! if true Sq=>-q+G symmetry is used
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logical, intent(inout) :: sym (48)
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! on input: .true. if symm. op. has to be tested
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! on output: .true. if symm. op. does not change mode modenum
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!
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integer :: isym, nas, ipols, na, sna, ipol, jpol
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! counters
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real(DP) :: arg
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! auxiliary
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complex(DP), allocatable :: u (:,:)
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! the original pattern
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complex(DP) :: fase, sum
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! the phase of the mode
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! check for orthogonality
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complex(DP), allocatable :: work_u (:,:), work_ru (:,:)
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! the working pattern
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! the rotated working pattern
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allocate(u(3, nat), work_u(3, nat), work_ru (3, nat))
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if (modenum > 3*nat .or. modenum < 1) call errore ('mode_group', &
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'wrong modenum', 1)
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nas = (modenum - 1) / 3 + 1
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ipols = mod (modenum - 1, 3) + 1
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u (:,:) = (0.d0, 0.d0)
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u (ipols, nas) = (1.d0, 0.d0)
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do na = 1, nat
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call trnvecc (u (1, na), at, bg, - 1)
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enddo
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do isym = 1, nrot
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if (sym (isym) ) then
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do na = 1, nat
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do ipol = 1, 3
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work_u (ipol, na) = u (ipol, na)
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enddo
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enddo
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work_ru (:,:) = (0.d0, 0.d0)
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do na = 1, nat
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sna = irt (isym, na)
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arg = 0.d0
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do ipol = 1, 3
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arg = arg + xq (ipol) * rtau (ipol, isym, na)
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enddo
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arg = arg * tpi
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if (isym.eq.nrot.and.minus_q) then
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fase = CMPLX(cos (arg), sin (arg) ,kind=DP)
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else
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fase = CMPLX(cos (arg), - sin (arg) ,kind=DP)
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endif
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do ipol = 1, 3
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do jpol = 1, 3
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work_ru (ipol, sna) = work_ru (ipol, sna) + s (jpol, ipol, &
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isym) * work_u (jpol, na) * fase
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enddo
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enddo
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enddo
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!
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! Transform back the rotated pattern
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!
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do na = 1, nat
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call trnvecc (work_ru (1, na), at, bg, 1)
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call trnvecc (work_u (1, na), at, bg, 1)
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enddo
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!
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! only if the pattern remain the same up to a phase we keep
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! the symmetry
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!
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sum = (0.d0, 0.d0)
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do na = 1, nat
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do ipol = 1, 3
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sum = sum + CONJG(work_u (ipol, na) ) * work_ru (ipol, na)
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enddo
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enddo
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sum = abs (sum)
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if (abs (sum - 1.d0) .gt.1.d-7) sym (isym) = .false.
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endif
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enddo
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deallocate ( work_ru, work_u, u)
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return
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end subroutine mode_group
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