mirror of https://gitlab.com/QEF/q-e.git
91 lines
2.8 KiB
Fortran
91 lines
2.8 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 dielec_test
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!-----------------------------------------------------------------------
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!! Calculates the dielectric tensor using the finite-differences-derivative
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!! of the wavefunctions. This should be used only for testing purposes
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!! while doing a raman calculation.
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!
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USE kinds, ONLY : DP
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USE constants,ONLY : fpi
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USE cell_base,ONLY : omega, at, bg
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USE klist, ONLY : wk, ngk
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USE symme, ONLY : symmatrix, crys_to_cart
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USE buffers, ONLY : get_buffer
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USE wavefunctions, ONLY: evc
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USE efield_mod, ONLY : epsilon
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USE qpoint, ONLY : nksq
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USE eqv, ONLY : dpsi
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USE control_lr, ONLY : nbnd_occ
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USE units_lr, ONLY : lrwfc, iuwfc
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USE ramanm, ONLY : a1j, a2j, lrd2w, iud2w
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USE mp_pools, ONLY : inter_pool_comm
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USE mp_bands, ONLY : intra_bgrp_comm
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USE mp, ONLY : mp_sum
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implicit none
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INTEGER :: npw
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integer :: ibnd, ipol, jpol, nrec, ik, i1, i2
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real(DP) :: w_, weight, tmp
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complex(DP), external :: zdotc
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epsilon (:,:) = 0.d0
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do ik = 1, nksq
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npw = ngk(ik)
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weight = wk (ik)
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w_ = - fpi * weight / omega
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call get_buffer (evc, lrwfc, iuwfc, ik)
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do ipol = 1, 6
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nrec = (ipol - 1) * nksq + ik
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call davcio (dpsi, lrd2w, iud2w, nrec, -1)
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tmp = 0.d0
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do ibnd = 1, nbnd_occ (ik)
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tmp = tmp + 2.0d0 * w_ * &
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real (zdotc (npw, evc (1, ibnd), 1, dpsi (1, ibnd), 1))
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enddo
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i1 = a1j (ipol)
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i2 = a2j (ipol)
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epsilon (i1, i2) = epsilon (i1, i2) + tmp
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if (i1.ne.i2 ) epsilon (i2, i1) = epsilon (i2, i1) + tmp
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enddo
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enddo
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call mp_sum ( epsilon, intra_bgrp_comm )
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call mp_sum ( epsilon, inter_pool_comm )
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!
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! symmetrize (pass to cartesian axis first)
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!
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! write(6,'(/,10x,''Unsymmetrized in crystal axis '',/)')
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! write(6,'(10x,''('',3f15.5,'' )'')') ((epsilon(ipol,jpol), &
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! ipol=1,3),jpol=1,3)
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call crys_to_cart (epsilon)
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call symmatrix(epsilon)
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!
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! write(6,'(/,10x,''Symmetrized in cartesian axis '',/)')
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! write(6,'(10x,''('',3f15.5,'' )'')') ((epsilon(ipol,jpol), &
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! ipol=1,3),jpol=1,3)
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!
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! add the diagonal part
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!
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do ipol = 1, 3
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epsilon (ipol, ipol) = epsilon (ipol, ipol) + 1.d0
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end do
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!
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! and print the result
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!
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write(6,'(/,10x,''Dielectric constant from finite-differences'',/)')
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write(6,'(10x,''('',3f18.9,'' )'')') ((epsilon(ipol,jpol), &
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ipol=1,3),jpol=1,3)
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return
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end subroutine dielec_test
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