mirror of https://gitlab.com/QEF/q-e.git
102 lines
3.0 KiB
Fortran
102 lines
3.0 KiB
Fortran
!
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! Copyright (C) 2001-2007 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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!----------------------------------------------------------------------
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subroutine setlocq (xq, mesh, msh, rab, r, vloc_at, zp, tpiba2, ngm, &
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g, omega, vloc)
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!----------------------------------------------------------------------
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!
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! This routine computes the Fourier transform of the local
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! part of the pseudopotential in the q+G vectors.
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!
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! The local pseudopotential of the US case is always in
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! numerical form, expressed in Ry units.
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!
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#include "f_defs.h"
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USE kinds, only : DP
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USE constants, ONLY : e2, fpi, pi
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!
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implicit none
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!
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! first the dummy variables
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!
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integer :: ngm, mesh, msh
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! input: the number of G vectors
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! input: the dimensions of the mesh
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! input: mesh points for radial integration
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real(DP) :: xq (3), zp, rab (mesh), r (mesh), vloc_at(mesh), tpiba2,&
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omega, g (3, ngm), vloc (ngm)
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! input: the q point
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! input: valence pseudocharge
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! input: the derivative of mesh points
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! input: the mesh points
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! input: the pseudo on the radial
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! input: 2 pi / alat
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! input: the volume of the unit cell
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! input: the g vectors coordinates
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! output: the fourier transform of the potential
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!
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! and the local variables
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!
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real(DP), parameter :: eps = 1.d-8
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real(DP) :: vlcp, vloc0, fac, den1, den2, g2a, g2a1, aux (mesh), &
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aux1 (mesh), gx
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! auxiliary variables
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! gx = modulus of g vectors
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real(DP), external :: erf
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! the erf function
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integer :: i, ig, l, ir
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! counters
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!
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! Pseudopotentials in numerical form (Vnl(lloc) contain the local part)
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! in order to perform the Fourier transform, a term erf(r)/r is
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! subtracted in real space and added again in G space
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!
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! first the G=0 term
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!
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do ir = 1, msh
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aux (ir) = r (ir) * (r (ir) * vloc_at (ir) + zp * e2)
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enddo
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call simpson (msh, aux, rab, vloc0)
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!
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! here the G<>0 terms, we first compute the part of the integrand func
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! indipendent of |G| in real space
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!
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do ir = 1, msh
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aux1 (ir) = r (ir) * vloc_at (ir) + zp * e2 * erf (r (ir) )
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enddo
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fac = zp * e2 / tpiba2
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!
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! and here we perform the integral, after multiplying for the |G|
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! dependent part
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!
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do ig = 1, ngm
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g2a = (xq (1) + g (1, ig) ) **2 + (xq (2) + g (2, ig) ) **2 + &
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(xq (3) + g (3, ig) ) **2
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if (g2a < eps) then
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vloc (ig) = vloc0
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else
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gx = sqrt (g2a * tpiba2)
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do ir = 1, msh
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aux (ir) = aux1 (ir) * sin (gx * r (ir) ) / gx
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enddo
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call simpson (msh, aux, rab, vlcp)
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!
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! here we add the analytic fourier transform of the erf function
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!
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vlcp = vlcp - fac * exp ( - g2a * tpiba2 * 0.25d0) / g2a
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vloc (ig) = vlcp
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endif
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enddo
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vloc(:) = vloc(:) * fpi / omega
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return
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end subroutine setlocq
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