mirror of https://gitlab.com/QEF/q-e.git
111 lines
3.5 KiB
Fortran
111 lines
3.5 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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subroutine smallg_q (xq, iswitch, at, bg, nrot, s, ftau, nr1, nr2, &
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nr3, sym, minus_q)
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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 q unchanged.
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! Furthermore it checks if one of the above matrices send q --> -q+G.
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! In this case minus_q is set true.
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#include"machine.h"
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!
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! input-output variables
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!
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use parameters
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implicit none
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real(kind=DP) :: bg (3, 3), at (3, 3), xq (3)
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! input: the reciprocal lattice vectors
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! input: the direct lattice vectors
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! input: the q point of the crystal
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integer :: s (3, 3, 48), nrot, nr1, nr2, nr3, ftau (3, 48), &
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iswitch
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! input: the symmetry matrices
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! input: number of symmetry operations
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! input: fft grid dimension (units for ftau)
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! input: fractionary translation of each symmetr
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! input: main switch of the program, used for
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! q<>0 to restrict the small group of q
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! to operation such that Sq=q (exactly,
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! without G vectors) when iswitch = -3.
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logical :: sym (48), minus_q
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! input-output: .true. if symm. op. S q = q + G
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! output: .true. if there's an op. sym.: S q = -
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!
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! local variables
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!
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real(kind=DP) :: aq (3), raq (3), zero (3)
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! q vector in crystal basis
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! the rotated of the q vector
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! the zero vector
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integer :: irot, ipol, jpol
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! counter on symmetry op.
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! counter on polarizations
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! counter on polarizations
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logical :: eqvect
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! logical function, check if two vectors are equa
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!
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! return immediately (with minus_q=.true.) if xq.eq.(0,0,0)
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!
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minus_q = .true.
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if (xq (1) .eq.0.d0.and.xq (2) .eq.0.d0.and.xq (3) .eq.0.d0) &
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return
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!
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! Set to zero some variables
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!
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minus_q = .false.
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zero(:) = 0.d0
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!
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! Transform xq to the crystal basis
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!
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call DCOPY (3, xq, 1, aq, 1)
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call cryst_to_cart (1, aq, at, - 1)
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!
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! Test all symmetries to see if this operation send S q in q+G or in -
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!
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do irot = 1, nrot
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if (.not.sym (irot) ) goto 100
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raq(:) = 0.d0
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do ipol = 1, 3
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do jpol = 1, 3
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raq(ipol) = raq(ipol) + float( s(ipol,jpol,irot) ) * aq( jpol)
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enddo
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enddo
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sym (irot) = eqvect (raq, aq, zero)
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!
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! if "iswitch.le.-3" S must be such that Sq=q exactly !
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!
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if (iswitch.le. -3.and.sym (irot) ) then
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do ipol = 1, 3
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sym(irot) = sym(irot) .and. abs(raq(ipol)-aq(ipol)).lt.1.0d-5
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enddo
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endif
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if (sym (irot) .and..not.minus_q) then
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! l'istruzione "originale" in kreductor era la seguente...
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! if (.not. minus_q) then
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call DSCAL (3, - 1.d0, raq, 1)
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minus_q = eqvect (raq, aq, zero)
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endif
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100 continue
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enddo
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!
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! if "iswitch.le.-3" time reversal symmetry is not included !
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!
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if (iswitch.le. -3) minus_q = .false.
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return
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end subroutine smallg_q
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