mirror of https://gitlab.com/QEF/q-e.git
63 lines
1.3 KiB
Fortran
63 lines
1.3 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 volume (alat, a1, a2, a3, omega)
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!---------------------------------------------------------------------
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!
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! Compute the volume of the unit cell
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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 I/O variables
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!
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real(DP) :: alat, a1 (3), a2 (3), a3 (3), omega
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! input: lattice parameter (unit length)
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! input: the first lattice vector
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! input: the second lattice vector
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! input: the third lattice vector
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! input: the volume of the unit cell
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!
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! Here the local variables required by the routine
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!
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real(DP) :: s
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! the sign of a permutation
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integer :: i, j, k, l, iperm
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!\
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! \
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! / auxiliary indices
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!/
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! counter on permutations
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!
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! Compute the volume
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!
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omega = 0.d0
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s = 1.d0
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i = 1
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j = 2
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k = 3
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101 do iperm = 1, 3
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omega = omega + s * a1 (i) * a2 (j) * a3 (k)
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l = i
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i = j
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j = k
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k = l
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enddo
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i = 2
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j = 1
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k = 3
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s = - s
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if (s.lt.0.d0) goto 101
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omega = abs (omega) * alat**3
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return
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end subroutine volume
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