mirror of https://gitlab.com/QEF/q-e.git
39 lines
1.2 KiB
Fortran
39 lines
1.2 KiB
Fortran
!
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! Copyright (C) 2017 Quantum ESPRESSO Foundation
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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 defined by 3 vectors
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! a1, a2, a3, given in units of "alat" (alat may be 1):
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! omega = alat^3 * [ a1 . (a2 x a3) ]
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! ( . = scalar product, x = vector product )
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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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REAL(dp), INTENT(IN) :: alat, a1(3), a2(3), a3(3)
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REAL(dp), INTENT(OUT) :: omega
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!
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omega = a1(1) * ( a2(2)*a3(3)-a2(3)*a3(2) ) - &
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a1(2) * ( a2(1)*a3(3)-a2(3)*a3(1) ) + &
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a1(3) * ( a2(1)*a3(2)-a2(2)*a3(1) )
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!
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IF ( omega < 0.0_dp) THEN
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call infomsg('volume','axis vectors are left-handed')
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omega = ABS (omega)
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END IF
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!
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IF ( alat < 1.0_dp) call infomsg('volume','strange lattice parameter')
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omega = omega * alat**3
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!
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RETURN
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!
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END SUBROUTINE volume
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