fourier_shell.F90

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!! Copyright (C) 2002-2011 M. Marques, A. Castro, A. Rubio, G. Bertsch, M. Oliveira
!!
!! This program is free software; you can redistribute it and/or modify
!! it under the terms of the GNU General Public License as published by
!! the Free Software Foundation; either version 2, or (at your option)
!! any later version.
!!
!! This program is distributed in the hope that it will be useful,
!! but WITHOUT ANY WARRANTY; without even the implied warranty of
!! MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
!! GNU General Public License for more details.
!!
!! You should have received a copy of the GNU General Public License
!! along with this program; if not, write to the Free Software
!! Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
!! 02110-1301, USA.
!!
 
#include "global.h"
 
module fourier_shell_oct_m
  use cube_oct_m
  use debug_oct_m
  use fft_oct_m
  use global_oct_m
  use, intrinsic :: iso_fortran_env
  use mesh_oct_m
  use messages_oct_m
  use namespace_oct_m
  use profiling_oct_m
  use space_oct_m
  use sort_oct_m
 
  implicit none
 
  private
  public ::                        &
    fourier_shell_t,               &
    fourier_shell_cutoff,          &
    fourier_shell_init,            &
    fourier_shell_end
 
  type fourier_shell_t
    ! Components are public by default
    integer              :: ngvectors
    real(real64)         :: ekin_cutoff
    integer, allocatable :: coords(:, :)
    integer, allocatable :: red_gvec(:, :)
  end type fourier_shell_t
 
contains
 
  real(real64) function fourier_shell_cutoff(space, cube, mesh, is_wfn, dg)
    class(space_t),  intent(in)  :: space
    type(cube_t),    intent(in)  :: cube
    class(mesh_t),   intent(in)  :: mesh
    logical,         intent(in)  :: is_wfn
    real(real64), optional, intent(out) :: dg(:)
 
    real(real64) :: dg_(3), gbound(3)
 
    push_sub(fourier_shell_cutoff)
 
    dg_(1:3) = m_two * m_pi/(cube%rs_n_global(1:3)*mesh%spacing(1:3))
    if (present(dg)) dg(1:3) = dg_(1:3)
    if (is_wfn .and. space%is_periodic()) then
      ! Note from Alex: -2 margin: the n_i = N_i/2 plane is excluded for even grids, and G+k with a
      ! reduced k-point shift of up to 1/2 must remain representable
      ! Apparently -2 can still miss lying on the sphere cutoff, but
      ! changing to Nᵢ/2 − 1 will change the G-vector count in existing BGW output
      gbound(1:3) = dg_(1:3)*(cube%rs_n_global(1:3)/2-2)
    else
      gbound(1:3) = dg_(1:3)*(cube%rs_n_global(1:3)/2)
    end if
    fourier_shell_cutoff = minval(gbound(1:3)**2)/m_two
 
    pop_sub(fourier_shell_cutoff)
  end function fourier_shell_cutoff
 
  subroutine fourier_shell_init(this, namespace, space, cube, mesh, kk)
    type(fourier_shell_t), intent(inout) :: this
    type(namespace_t),     intent(in)    :: namespace
    class(space_t),        intent(in)    :: space
    type(cube_t),          intent(in)    :: cube
    class(mesh_t),         intent(in)    :: mesh
    real(real64), optional,       intent(in)    :: kk(:)
 
    integer :: ig, ix, iy, iz, ixx(1:3), imap
    real(real64) :: dg(1:3), gvec(1:3)
    real(real64), allocatable :: modg2(:)
    integer, allocatable :: map(:), ucoords(:, :), ured_gvec(:, :)
    integer(int64) :: number_points
 
    push_sub(fourier_shell_init)
 
    this%ekin_cutoff = fourier_shell_cutoff(space, cube, mesh, present(kk), dg = dg)
 
    ! make sure we do not run into integer overflow here
    number_points = cube%rs_n_global(1) * cube%rs_n_global(2)
    number_points = number_points * cube%rs_n_global(3)
    if (number_points >= huge(0)) then
      message(1) = "Error: too many points for the normal cube. Please try to use a distributed FFT."
      call messages_fatal(1, namespace=namespace)
    end if
    safe_allocate(modg2(1:product(cube%rs_n_global(1:3))))
    safe_allocate(ucoords(1:3, 1:product(cube%rs_n_global(1:3))))
    safe_allocate(ured_gvec(1:3, 1:product(cube%rs_n_global(1:3))))
 
    ig = 0
    ! According to the conventions of plane-wave codes, e.g. Quantum ESPRESSO,
    ! PARATEC, EPM, and BerkeleyGW, if the FFT grid is even, then neither
    ! nfft/2 nor -nfft/2 should be a valid G-vector component.
    do ix = 1, cube%rs_n_global(1)
      ixx(1) = pad_feq(ix, cube%rs_n_global(1), .true.)
      if (2 * ixx(1) == cube%rs_n_global(1)) cycle
      do iy = 1, cube%rs_n_global(2)
        ixx(2) = pad_feq(iy, cube%rs_n_global(2), .true.)
        if (2 * ixx(2) == cube%rs_n_global(2)) cycle
        do iz = 1, cube%rs_n_global(3)
          ixx(3) = pad_feq(iz, cube%rs_n_global(3), .true.)
          if (2 * ixx(3) == cube%rs_n_global(3)) cycle
 
          if (present(kk)) then
            gvec(1:3) = dg(1:3)*(ixx(1:3) + kk(1:3))
          else
            gvec(1:3) = dg(1:3)*ixx(1:3)
          end if
          gvec(1:3) = matmul(cube%latt%klattice_primitive(1:3, 1:3), gvec(1:3))
 
          if (sum(gvec(1:3)**2)/m_two <= this%ekin_cutoff + 1e-10_real64) then
            ig = ig + 1
            ucoords(1:3, ig) = (/ ix, iy, iz /)
            ured_gvec(1:3, ig) = ixx(1:3)
            modg2(ig) = sum(gvec(1:3)**2)
          end if
 
        end do
      end do
    end do
 
    this%ngvectors = ig
 
    safe_allocate(this%coords(1:3, 1:this%ngvectors))
    safe_allocate(this%red_gvec(1:3, 1:this%ngvectors))
    safe_allocate(map(1:this%ngvectors))
 
    do ig = 1, this%ngvectors
      map(ig) = ig
    end do
 
    call sort(modg2(1:this%ngvectors), map)
 
    do ig = 1, this%ngvectors
      imap = map(ig)
      this%coords(1:3, ig) = ucoords(1:3, imap)
      this%red_gvec(1:3, ig) = ured_gvec(1:3, imap)
    end do
 
    safe_deallocate_a(ucoords)
    safe_deallocate_a(ured_gvec)
    safe_deallocate_a(modg2)
    safe_deallocate_a(map)
 
    pop_sub(fourier_shell_init)
  end subroutine fourier_shell_init
 
  ! -----------------------------------------------------
 
  subroutine fourier_shell_end(this)
    type(fourier_shell_t), intent(inout) :: this
 
    push_sub(fourier_shell_end)
 
    safe_deallocate_a(this%coords)
    safe_deallocate_a(this%red_gvec)
 
    pop_sub(fourier_shell_end)
  end subroutine fourier_shell_end
 
end module fourier_shell_oct_m
 
!! Local Variables:
!! mode: f90
!! coding: utf-8
!! End: