kick.F90

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!! Copyright (C) 2002-2006 M. Marques, A. Castro, A. Rubio, G. Bertsch
!!
!! 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 kick_oct_m
  use debug_oct_m
  use global_oct_m
  use electron_space_oct_m
  use iso_c_binding
  use ion_dynamics_oct_m
  use ions_oct_m
  use, intrinsic :: iso_fortran_env
  use kpoints_oct_m
  use loct_math_oct_m
  use math_oct_m
  use mesh_oct_m
  use messages_oct_m
  use namespace_oct_m
  use parser_oct_m
  use pcm_eom_oct_m
  use pcm_oct_m
  use poisson_oct_m
  use profiling_oct_m
  use species_oct_m
  use space_oct_m
  use states_elec_oct_m
  use states_elec_dim_oct_m
  use symm_op_oct_m
  use symmetries_oct_m
  use unit_oct_m
  use unit_system_oct_m
  use write_iter_oct_m
 
  implicit none
 
  private
  public ::               &
    kick_t,               &
    kick_init,            &
    kick_copy,            &
    kick_end,             &
    kick_read,            &
    kick_write,           &
    kick_apply,           &
    kick_function_get,    &
    kick_get_type
 
 
  integer, public, parameter ::        &
    KICK_FUNCTION_DIPOLE        = 0,   &
    kick_function_multipole     = 1,   &
    kick_function_user_defined  = 2
 
  integer, public, parameter ::    &
    KICK_DENSITY_MODE        = 0,  &
    kick_spin_mode           = 1,  &
    kick_spin_density_mode   = 2,  &
    kick_magnon_mode         = 3
 
  integer, public, parameter ::    &
    QKICKMODE_NONE           = 0,  &
    qkickmode_exp            = 1,  &
    qkickmode_cos            = 2,  &
    qkickmode_sin            = 3,  &
    qkickmode_bessel         = 4
 
 
  type kick_t
    ! Components are public by default
 
    integer           :: dim
    real(real64)      :: time
    integer, private  :: delta_strength_mode
    real(real64)      :: delta_strength
    real(real64), allocatable :: pol(:,:)
    integer            :: pol_dir
    integer            :: pol_equiv_axes
    real(real64), allocatable :: wprime(:)
    real(real64)       :: easy_axis(3)
    integer              :: n_multipoles
    integer, allocatable :: l(:), m(:)
    real(real64),   allocatable :: weight(:)
    integer              :: nqmult(3)
    integer              :: nqvec
    real(real64),   allocatable :: qvector(:,:)
    real(real64)         :: trans_vec(3, 2)
    real(real64)         :: qlength
    integer              :: qkick_mode
    integer              :: qbessel_l, qbessel_m
    integer              :: function_mode
    character(len=200), private:: user_defined_function
  end type kick_t
 
contains
 
  ! ---------------------------------------------------------
  subroutine kick_init(kick, namespace, space, kpoints, nspin)
    type(kick_t),      intent(inout) :: kick
    type(namespace_t), intent(in)  :: namespace
    class(space_t),    intent(in)  :: space
    type(kpoints_t),   intent(in)  :: kpoints
    integer,           intent(in)  :: nspin
 
    type(block_t) :: blk
    integer :: n_rows, irow, idir, iop, iq, iqx, iqy, iqz
    real(real64) :: norm, dot
    real(real64) :: qtemp(space%dim)
    integer :: periodic_dim
 
    push_sub(kick_init)
 
    kick%dim = space%dim
    periodic_dim = space%periodic_dim
    kick%nqvec = 0
 
    safe_allocate(kick%pol(1:space%dim, 1:space%dim))
    safe_allocate(kick%wprime(1:space%dim))
 
    !%Variable TDDeltaKickTime
    !%Type float
    !%Default 0.0
    !%Section Time-Dependent::Response
    !%Description
    !% The delta-perturbation that can be applied by making use of the <tt>TDDeltaStrength</tt> variable,
    !% can be applied at the time given by this variable. Usually, this time is zero, since one wants
    !% to apply the delta pertubation or "kick" at a system at equilibrium, and no other time-dependent
    !% external potential is used. However, one may want to apply a kick on top of a laser field,
    !% for example.
    !%End
    call parse_variable(namespace, 'TDDeltaKickTime', m_zero, kick%time, units_inp%time)
    if (kick%time > m_zero) then
      call messages_experimental('TDDeltaKickTime > 0', namespace=namespace)
    end if
 
    !%Variable TDDeltaStrength
    !%Type float
    !%Default 0
    !%Section Time-Dependent::Response
    !%Description
    !% When no laser is applied, a delta (in time) perturbation with
    !% strength <tt>TDDeltaStrength</tt> can be applied. This is used to
    !% calculate, <i>e.g.</i>, the linear optical spectra. If the ions are
    !% allowed to move, the kick will affect them also.
    !% The electric field is <math>-(\hbar k / e) \delta(t)</math> for a dipole with
    !% zero wavevector, where <i>k</i> = <tt>TDDeltaStrength</tt>, which causes
    !% the wavefunctions instantaneously to acquire a phase <math>e^{ikx}</math>.
    !% The unit is inverse length.
    !%End
    call parse_variable(namespace, 'TDDeltaStrength', m_zero, kick%delta_strength, units_inp%length**(-1))
 
    kick%function_mode = kick_function_dipole
 
    if (abs(kick%delta_strength) <= m_epsilon) then
      kick%delta_strength_mode = 0
      kick%pol_equiv_axes = 0
      kick%pol = diagonal_matrix(kick%dim, m_one)
      kick%pol_dir = 0
      kick%wprime = m_zero
      kick%n_multipoles = 0
      kick%qkick_mode = qkickmode_none
      kick%easy_axis = m_zero
      pop_sub(kick_init)
      return
    end if
 
    !%Variable TDDeltaStrengthMode
    !%Type integer
    !%Default kick_density
    !%Section Time-Dependent::Response
    !%Description
    !% When calculating the density response via real-time propagation,
    !% one needs to perform an initial kick on the KS system, at
    !% time zero. Depending on what kind of response property one wants to obtain,
    !% this kick may be done in several modes. For use to calculate triplet excitations,
    !% see MJT Oliveira, A Castro, MAL Marques, and A Rubio, <i>J. Nanoscience and Nanotechnology</i> <b>8</b>, 3392 (2008).
    !%Option kick_density 0
    !% The total density of the system is perturbed. This mode is appropriate for
    !% electric dipole response, as for optical absorption.
    !%Option kick_spin 1
    !% The individual spin densities are perturbed oppositely. Note that this mode
    !% is only possible if the run is done in spin-polarized mode, or with spinors.
    !% This mode is appropriate for the paramagnetic dipole response, which can couple
    !% to triplet excitations.
    !%Option kick_spin_and_density 2
    !% A combination of the two above. Note that this mode
    !% is only possible if the run is done in spin-polarized mode, or with spinors.
    !% This mode is intended for use with symmetries to obtain both of the responses
    !% at once, at described in the reference above.
    !%Option kick_magnon 3
    !% Rotates the magnetization. Only works for spinors.
    !% Can be used in a supercell or my making use of the generalized Bloch theorem.
    !% In the later case (see <tt>SpiralBoundaryConditions</tt>) spin-orbit coupling cannot be used.
    !%End
    call parse_variable(namespace, 'TDDeltaStrengthMode', kick_density_mode, kick%delta_strength_mode)
    select case (kick%delta_strength_mode)
    case (kick_density_mode)
    case (kick_spin_mode, kick_spin_density_mode)
    case (kick_magnon_mode)
      if (nspin /= spinors) then
        call messages_input_error(namespace, 'TDDeltaStrengthMode', 'Magnon kick is incompatible with spinors')
      end if
    case default
      call messages_input_error(namespace, 'TDDeltaStrengthMode', 'Unknown mode')
    end select
 
    if (parse_is_defined(namespace, 'TDDeltaUserDefined')) then
 
      kick%function_mode = kick_function_user_defined
      kick%n_multipoles = 0
 
      !%Variable TDDeltaUserDefined
      !%Type string
      !%Section Time-Dependent::Response
      !%Description
      !% By default, the kick function will be a dipole. This will change if (1) the variable
      !% <tt>TDDeltaUserDefined</tt> is present in the inp file, or (2) if the block <tt>TDKickFunction</tt>
      !% is present in the <tt>inp</tt> file. If both are present in the <tt>inp</tt> file, the <tt>TDKickFunction</tt>
      !% block will be ignored. The value of <tt>TDDeltaUserDefined</tt> should be a string describing
      !% the function that is going to be used as delta perturbation.
      !%End
      call parse_variable(namespace, 'TDDeltaUserDefined', '0', kick%user_defined_function)
 
      !%Variable TDKickFunction
      !%Type block
      !%Section Time-Dependent::Response
      !%Description
      !% If the block <tt>TDKickFunction</tt> is present in the input file, and the variable
      !% <tt>TDDeltaUserDefined</tt> is not present in the input file, the kick function to
      !% be applied at time zero of the time-propagation will not be a "dipole" function
      !% (<i>i.e.</i> <math>\phi \rightarrow e^{ikx} \phi</math>, but a general multipole in the form <math>r^l Y_{lm}(r)</math>.
      !%
      !% Each line has three columns: integers <i>l</i> and <i>m</i> that defines the
      !% multipole, and a weight. Any number of lines may be given, and the kick will be the sum of those
      !% multipoles with the given weights.
      !%
      !% This feature allows calculation of quadrupole, octupole, etc., response functions.
      !%End
    else if (parse_block(namespace, 'TDKickFunction', blk) == 0) then
 
      kick%function_mode = kick_function_multipole
      n_rows = parse_block_n(blk)
      kick%n_multipoles = n_rows
      safe_allocate(     kick%l(1:n_rows))
      safe_allocate(     kick%m(1:n_rows))
      safe_allocate(kick%weight(1:n_rows))
      do irow = 1, n_rows
        call parse_block_integer(blk, irow - 1, 0, kick%l(irow))
        call parse_block_integer(blk, irow - 1, 1, kick%m(irow))
        call parse_block_float(blk, irow - 1, 2, kick%weight(irow))
        if ((kick%l(irow) < 0) .or. (abs(kick%m(irow)) > abs(kick%l(irow)))) then
          call messages_input_error(namespace, 'TDkickFunction')
        end if
      end do
 
    else
 
      kick%function_mode = kick_function_dipole
      kick%n_multipoles = 0
 
      ! Find out how many equivalent axes we have...
      !%Variable TDPolarizationEquivAxes
      !%Type integer
      !%Default 0
      !%Section Time-Dependent::Response::Dipole
      !%Description
      !% Defines how many of the <tt>TDPolarization</tt> axes are equivalent. This information is stored in a file and then
      !% used by <tt>oct-propagation_spectrum</tt> to rebuild the full polarizability tensor from just the
      !% first <tt>TDPolarizationEquivAxes</tt> directions. This variable is also used by <tt>CalculationMode = vdw</tt>.
      !%End
      call parse_variable(namespace, 'TDPolarizationEquivAxes', 0, kick%pol_equiv_axes)
 
      !%Variable TDPolarizationDirection
      !%Type integer
      !%Section Time-Dependent::Response::Dipole
      !%Description
      !% When a delta potential is included in a time-dependent run, this
      !% variable defines in which direction the field will be applied
      !% by selecting one of the lines of <tt>TDPolarization</tt>. In a
      !% typical run (without using symmetry), the <tt>TDPolarization</tt> block
      !% would contain the three Cartesian unit vectors (the default
      !% value), and one would make 3 runs varying
      !% <tt>TDPolarization</tt> from 1 to 3.
      !% If one is using symmetry,  <tt>TDPolarization</tt> should run only from 1
      !% to <tt>TDPolarizationEquivAxes</tt>.
      !%End
 
      call parse_variable(namespace, 'TDPolarizationDirection', 0, kick%pol_dir)
 
      if (kick%delta_strength_mode /= kick_magnon_mode) then
        if (kick%pol_dir < 1 .or. kick%pol_dir > kick%dim) call messages_input_error(namespace, 'TDPolarizationDirection')
      end if
 
      !%Variable TDPolarization
      !%Type block
      !%Section Time-Dependent::Response::Dipole
      !%Description
      !% The (real) polarization of the delta electric field. Normally
      !% one needs three perpendicular polarization directions to calculate a
      !% spectrum (unless symmetry is used).
      !% The format of the block is:
      !%
      !% <tt>%TDPolarization
      !% <br>&nbsp;&nbsp;pol1x | pol1y | pol1z
      !% <br>&nbsp;&nbsp;pol2x | pol2y | pol2z
      !% <br>&nbsp;&nbsp;pol3x | pol3y | pol3z
      !% <br>%</tt>
      !%
      !% <tt>Octopus</tt> uses both this block and the variable
      !% <tt>TDPolarizationDirection</tt> to determine the polarization
      !% vector for the run. For example, if
      !% <tt>TDPolarizationDirection=2</tt> the polarization <tt>(pol2x,
      !% pol2y, pol2z)</tt> would be used.
      !% These directions may not be in periodic directions.
      !%
      !% The default value for <tt>TDPolarization</tt> is the three
      !% Cartesian unit vectors (1,0,0), (0,1,0), and (0,0,1).
      !%
      !% Note that the directions do not necessarily need to be perpendicular
      !% when symmetries are used.
      !%
      !% WARNING: If you want to obtain the cross-section tensor, the
      !% <tt>TDPolarization</tt> block must be exactly the same for the run in
      !% each direction. The direction must be selected by the
      !% <tt>TDPolarizationDirection</tt> variable.
      !%
      !%End
 
      ! Default basis is the Cartesian unit vectors.
      ! FIXME: Here the symmetry of the system should be analyzed, and the polarization
      ! basis built accordingly.
      kick%pol(1:kick%dim, 1:kick%dim) = diagonal_matrix(kick%dim, m_one)
      if (parse_block(namespace, 'TDPolarization', blk) == 0) then
        n_rows = parse_block_n(blk)
 
        if (n_rows /= kick%dim) then
          call messages_input_error(namespace, 'TDPolarization', 'There should be exactly one line per dimension')
        end if
 
        do irow = 1, n_rows
          do idir = 1, kick%dim
            call parse_block_float(blk, irow - 1, idir - 1, kick%pol(idir, irow))
          end do
        end do
        call parse_block_end(blk)
      end if
 
      ! Normalize
      do idir = 1, kick%dim
        kick%pol(1:kick%dim, idir) = kick%pol(1:kick%dim, idir) / norm2(kick%pol(1:kick%dim, idir))
      end do
 
      if (kick%delta_strength_mode /= kick_magnon_mode) then
        if (any(abs(kick%pol(1:periodic_dim, :)) > m_epsilon)) then
          message(1) = "Kick cannot be applied in a periodic direction. Use GaugeVectorField instead."
          call messages_fatal(1, namespace=namespace)
        end if
      end if
 
      !%Variable TDPolarizationWprime
      !%Type block
      !%Section Time-Dependent::Response::Dipole
      !%Description
      !% This block is needed only when
      !% <tt>TDPolarizationEquivAxes</tt> is set to 3.  In such a case,
      !% the three directions (<i>pol1</i>, <i>pol2</i>, and <i>pol3</i>) defined in
      !% the <tt>TDPolarization</tt> block should be related by symmetry
      !% operations. If <i>A</i> is the symmetry operation that takes you
      !% from <i>pol1</i> to <i>pol2</i>, then <tt>TDPolarizationWprime</tt>
      !% should be set to the direction defined by <i>A</i><math>^{-1}</math><i>pol3</i>.
      !% For more information see MJT Oliveira
      !% <i>et al.</i>, <i>J. Nanoscience and Nanotechnology</i> <b>8</b>,
      !% 3392 (2008).
      !%End
      if (parse_block(namespace, 'TDPolarizationWprime', blk) == 0) then
        do idir = 1, kick%dim
          call parse_block_float(blk, 0, idir - 1, kick%wprime(idir))
        end do
        kick%wprime(1:kick%dim) = kick%wprime(1:kick%dim) / norm2(kick%wprime(1:kick%dim))
        call parse_block_end(blk)
      else
        kick%wprime(1:kick%dim-1) = m_zero
        kick%wprime(kick%dim) = m_one
      end if
    end if
 
    ! for non-dipole, it is more complicated to check whether it is actually in the periodic direction
    if (periodic_dim > 0 .and. kick%delta_strength_mode /= kick_magnon_mode) then
      message(1) = "Kicks cannot be applied correctly in periodic directions."
      call messages_warning(1, namespace=namespace)
    end if
 
 
    !%Variable TDReducedMomentumTransfer
    !%Type block
    !%Section Time-Dependent::Response
    !%Description
    !% The same as TDMomentumTransfer, but the momentum is specified in reduced coordinates.
    !% Only available for magnon kicks at the moment, and only with an exponential kick.
    !%End
    if (periodic_dim > 0 .and. kick%delta_strength_mode == kick_magnon_mode .and. &
      parse_block(namespace, 'TDReducedMomentumTransfer', blk) == 0) then
 
      kick%nqvec = 1
      safe_allocate(kick%qvector(1:kick%dim, 1))
      do idir = 1, kick%dim
        call parse_block_float(blk, 0, idir - 1, qtemp(idir))
      end do
      call kpoints_to_absolute(kpoints%latt, qtemp(1:kick%dim), kick%qvector(:, 1))
      kick%qkick_mode = qkickmode_exp
 
      call parse_block_end(blk)
 
      if (kpoints%use_symmetries) then
        do iop = 1, symmetries_number(kpoints%symm)
          if (iop == symmetries_identity_index(kpoints%symm)) cycle
          if (.not. symm_op_invariant_cart(kpoints%symm%ops(iop), kick%qvector(:,1), 1e-5_real64)) then
            message(1) = "The TDMomentumTransfer breaks (at least) one of the symmetries used to reduce the k-points."
            message(2) = "Set SymmetryBreakDir equal to TDMomemtumTransfer."
            call messages_fatal(2, namespace=namespace)
          end if
        end do
      end if
 
      !%Variable TDMomentumTransfer
      !%Type block
      !%Section Time-Dependent::Response
      !%Description
      !% Momentum-transfer vector for the calculation of the dynamic structure factor.
      !% When this variable is set, a non-dipole field is applied, and an output file
      !% <tt>ftchd</tt> is created (it contains the Fourier transform of the charge density
      !% at each time). The type of the applied external field can be set by
      !% an optional last number. Possible options are <tt>qexp</tt> (default), <tt>qcos</tt>,
      !% <tt>qsin</tt>, or <tt>qcos+qsin</tt>. In the formulae below,
      !% <math>\vec{q}</math> is the momentum-transfer vector.
      !%Option qexp 1
      !% External field is <math>e^{i \vec{q} \cdot \vec{r}}</math>.
      !%Option qcos 2
      !% External field is <math>\cos \left( i \vec{q} \cdot \vec{r} \right)</math>.
      !%Option qsin 3
      !% External field is <math>\sin \left( i \vec{q} \cdot \vec{r} \right)</math>.
      !%Option qbessel 4
      !% External field is <math>j_l \left( \vec{q} \cdot \vec{r} \right) Y_{lm} \left(\vec{r} \right)</math>.
      !% In this case, the block has to include two extra values (<i>l</i> and <i>m</i>).
      !%End
 
    else if (parse_block(namespace, 'TDMomentumTransfer', blk) == 0) then
      kick%nqvec = 1
      safe_allocate(kick%qvector(1:kick%dim, 1))
      do idir = 1, kick%dim
        call parse_block_float(blk, 0, idir - 1, kick%qvector(idir,1))
        kick%qvector(idir,1) = units_to_atomic(unit_one / units_inp%length, kick%qvector(idir,1))
      end do
 
      ! Read the calculation mode (exp, cos, sin, or bessel)
      if (parse_block_cols(blk, 0) > 3) then
 
        call parse_block_integer(blk, 0, idir - 1, kick%qkick_mode)
 
        ! Read l and m if bessel mode (j_l*Y_lm) is used
        if (kick%qkick_mode == qkickmode_bessel .and. parse_block_cols(blk, 0) == 6) then
          call parse_block_integer(blk, 0, idir + 0, kick%qbessel_l)
          call parse_block_integer(blk, 0, idir + 1, kick%qbessel_m)
        else
          kick%qbessel_l = 0
          kick%qbessel_m = 0
        end if
 
      else
        kick%qkick_mode = qkickmode_exp
      end if
 
      call parse_block_end(blk)
 
      if (kpoints%use_symmetries) then
        do iop = 1, symmetries_number(kpoints%symm)
          if (iop == symmetries_identity_index(kpoints%symm)) cycle
          if (.not. symm_op_invariant_cart(kpoints%symm%ops(iop), kick%qvector(:,1), 1e-5_real64)) then
            message(1) = "The TDMomentumTransfer breaks (at least) one of the symmetries used to reduce the k-points."
            message(2) = "Set SymmetryBreakDir equal to TDMomemtumTransfer."
            call messages_fatal(2, namespace=namespace)
          end if
        end do
      end if
 
    else
      kick%qkick_mode = qkickmode_none
      kick%nqvec = 1
      safe_allocate(kick%qvector(1:kick%dim,1))
      kick%qvector(:,1) = m_zero
    end if
 
    kick%qlength = norm2(kick%qvector(:,1))
 
    if (kick%delta_strength_mode == kick_magnon_mode) then
      !%Variable TDEasyAxis
      !%Type block
      !%Section Time-Dependent::Response::Dipole
      !%Description
      !% For magnon kicks only.
      !% This variable defines the direction of the easy axis of the crystal.
      !% The magnetization is kicked in the plane transverse to this vector
      !%End
      if (parse_block(namespace, 'TDEasyAxis', blk) == 0) then
        n_rows = parse_block_n(blk)
 
        do idir = 1, 3
          call parse_block_float(blk, 0, idir - 1, kick%easy_axis(idir))
        end do
        norm = norm2(kick%easy_axis(1:3))
        if (norm < 1e-9_real64) then
          message(1) = "TDEasyAxis norm is too small."
          call messages_fatal(1, namespace=namespace)
        end if
        kick%easy_axis(1:3) = kick%easy_axis(1:3)/norm
        call parse_block_end(blk)
      else
        message(1) = "For magnons, the variable TDEasyAxis must be defined."
        call messages_fatal(1, namespace=namespace)
      end if
 
      !We first two vectors defining a basis in the transverse plane
      !For this we take two vectors not align with the first one
      !and we perform a Gram-Schmidt orthogonalization
      kick%trans_vec(1,1) = -kick%easy_axis(2)
      kick%trans_vec(2,1) = m_two*kick%easy_axis(3)
      kick%trans_vec(3,1) = m_three*kick%easy_axis(1)
 
      dot = sum(kick%easy_axis(1:3)*kick%trans_vec(1:3,1))
      kick%trans_vec(1:3,1) = kick%trans_vec(1:3,1) - dot*kick%easy_axis(1:3)
      norm = sum(kick%trans_vec(1:3,1)**2)
      kick%trans_vec(1:3,1) = kick%trans_vec(1:3,1)/sqrt(norm)
 
      !To get a direct basis, the last vector is obtained by the cross product
      kick%trans_vec(1,2) = kick%easy_axis(2) * kick%trans_vec(3,1) - kick%easy_axis(3) * kick%trans_vec(2,1)
      kick%trans_vec(2,2) = kick%easy_axis(3) * kick%trans_vec(1,1) - kick%easy_axis(1) * kick%trans_vec(3,1)
      kick%trans_vec(3,2) = kick%easy_axis(1) * kick%trans_vec(2,1) - kick%easy_axis(2) * kick%trans_vec(1,1)
 
      !The perturbation direction is defined as
      !cos(q.r)*uvec + sin(q.r)*vvec
 
 
      if (parse_is_defined(namespace, 'TDMomentumTransfer') &
        .and. parse_is_defined(namespace, 'TDMultipleMomentumTransfer')) then
        message(1) = "TDMomentumTransfer and TDMultipleMomentumTransfer cannot be defined at the same time."
        call messages_fatal(1, namespace=namespace)
      end if
 
      if (parse_is_defined(namespace, 'TDMultipleMomentumTransfer')) then
 
        kick%qkick_mode = qkickmode_exp
 
        !%Variable TDMultipleMomentumTransfer
        !%Type block
        !%Section Time-Dependent::Response
        !%Description
        !% For magnon kicks only.
        !% A simple way to specify momentum-transfer vectors for the calculation of
        !% the magnetization dynamics. This variable should be used for a supercell.
        !% For each reciprocal lattice vectors, the code will kick the original magnetization
        !% using all the multiples of it.
        !% The syntax reads:
        !%
        !% <tt>%TDMultipleMomentumTransfer
        !% <br>&nbsp;&nbsp;N_x | N_y | N_z
        !% <br>%</tt>
        !%
        !% and will include the (2N_x+1)*(2N_y+1)*(2N_z+1) multiples vectors of the reciprocal
        !% lattice vectors of the current cell.
        !%End
        if (parse_block(namespace, 'TDMultipleMomentumTransfer', blk) /= 0) then
          write(message(1),'(a)') 'Internal error while reading TDMultipleMomentumTransfer.'
          call messages_fatal(1, namespace=namespace)
        end if
 
        do idir = 1, 3
          call parse_block_integer(blk, 0, idir-1, kick%nqmult(idir))
        end do
 
        call parse_block_end(blk)
 
 
        kick%nqvec = (2*kick%nqmult(1)+1)*(2*kick%nqmult(2)+1)*(2*kick%nqmult(3)+1)
        !qvector has been allocated by default to a null vector before
        safe_deallocate_a(kick%qvector)
        safe_allocate(kick%qvector(1:3, 1:kick%nqvec))
        iq = 0
        do iqx = -kick%nqmult(1), kick%nqmult(1)
          do iqy = -kick%nqmult(2), kick%nqmult(2)
            do iqz = -kick%nqmult(3), kick%nqmult(3)
              iq = iq + 1
              qtemp(1:3) = (/iqx, iqy, iqz/)
              call kpoints_to_absolute(kpoints%latt, qtemp, kick%qvector(1:3, iq))
 
              !Checking symmetries for all G vectors
              if (kpoints%use_symmetries) then
                do iop = 1, symmetries_number(kpoints%symm)
                  if (iop == symmetries_identity_index(kpoints%symm)) cycle
                  if (.not. symm_op_invariant_cart(kpoints%symm%ops(iop), kick%qvector(:,iq), 1e-5_real64)) then
                    message(1) = "The TDMultipleMomentumTransfer breaks (at least) one " &
                      // "of the symmetries used to reduce the k-points."
                    message(2) = "Set SymmetryBreakDir accordingly."
                    call messages_fatal(2, namespace=namespace)
                  end if
                end do
              end if
            end do
          end do
        end do
 
      end if
 
    else
      kick%easy_axis(:) = m_zero
    end if
 
    if (kick%delta_strength_mode == kick_magnon_mode .and. kick%qkick_mode /= qkickmode_exp) then
      message(1) = "For magnons, the kick mode must be exponential."
      call messages_fatal(1, namespace=namespace)
    end if
 
    pop_sub(kick_init)
  end subroutine kick_init
 
 
  ! ---------------------------------------------------------
  subroutine kick_copy(kick_out, kick_in)
    type(kick_t), intent(inout) :: kick_out
    type(kick_t), intent(in)    :: kick_in
 
    push_sub(kick_copy)
 
    kick_out%dim = kick_in%dim
 
    kick_out%time = kick_in%time
 
    kick_out%delta_strength_mode = kick_in%delta_strength_mode
    kick_out%delta_strength = kick_in%delta_strength
 
    safe_allocate_source_a(kick_out%pol, kick_in%pol)
    kick_out%pol_dir = kick_in%pol_dir
    kick_out%pol_equiv_axes = kick_in%pol_equiv_axes
    safe_allocate_source_a(kick_out%wprime, kick_in%wprime)
 
    kick_out%n_multipoles = kick_in%n_multipoles
    if (kick_out%n_multipoles > 0) then
      safe_allocate_source_a(kick_out%l, kick_in%l)
      safe_allocate_source_a(kick_out%m, kick_in%m)
      safe_allocate_source_a(kick_out%weight, kick_in%weight)
    end if
    kick_out%nqvec = kick_in%nqvec
    safe_allocate_source_a(kick_out%qvector, kick_in%qvector)
    kick_out%qlength = kick_in%qlength
    kick_out%qkick_mode = kick_in%qkick_mode
    kick_out%qbessel_l = kick_in%qbessel_l
    kick_out%qbessel_m = kick_in%qbessel_m
 
    kick_out%function_mode = kick_in%function_mode
    kick_out%user_defined_function = kick_in%user_defined_function
 
    kick_out%easy_axis = kick_in%easy_axis
 
    pop_sub(kick_copy)
  end subroutine kick_copy
 
  ! ---------------------------------------------------------
  subroutine kick_end(kick)
    type(kick_t), intent(inout) :: kick
 
    push_sub(kick_end)
 
    kick%delta_strength_mode = 0
    kick%dim = 0
    kick%pol_equiv_axes = 0
    safe_deallocate_a(kick%pol)
    kick%pol_dir = 0
    safe_deallocate_a(kick%wprime)
    if (kick%n_multipoles > 0) then
      safe_deallocate_a(kick%l)
      safe_deallocate_a(kick%m)
      safe_deallocate_a(kick%weight)
    end if
    kick%n_multipoles = 0
    kick%qkick_mode = qkickmode_none
    safe_deallocate_a(kick%qvector)
 
    pop_sub(kick_end)
  end subroutine kick_end
 
  ! ---------------------------------------------------------
  subroutine kick_read(kick, iunit, namespace)
    type(kick_t),      intent(inout) :: kick
    integer,           intent(in)    :: iunit
    type(namespace_t), intent(in)    :: namespace
 
    integer :: idir, im, ierr
    character(len=100) :: line
 
    push_sub(kick_read)
 
    kick%function_mode = -1
 
    read(iunit, '(15x,i2)')     kick%delta_strength_mode
    read(iunit, '(15x,f18.12)') kick%delta_strength
    read(iunit, '(15x,i2)')     kick%dim
    read(iunit, '(a)') line
    if (index(line,'defined') /= 0) then
      kick%function_mode = kick_function_user_defined
      ! "# User defined: "
      read(line,'(16x,a)') kick%user_defined_function
    elseif (index(line,'multipole') /= 0) then
      kick%function_mode = kick_function_multipole
      ! "# N multipoles "
      read(line, '(15x,i3)') kick%n_multipoles
      safe_allocate(     kick%l(1:kick%n_multipoles))
      safe_allocate(     kick%m(1:kick%n_multipoles))
      safe_allocate(kick%weight(1:kick%n_multipoles))
      do im = 1, kick%n_multipoles
        ! "# multipole    "
        read(iunit, '(15x,2i3,f18.12)') kick%l(im), kick%m(im), kick%weight(im)
      end do
    else
      kick%function_mode = kick_function_dipole
      kick%n_multipoles = 0
      backspace(iunit)
 
      safe_allocate(kick%pol(1:kick%dim, 1:kick%dim))
      safe_allocate(kick%wprime(1:kick%dim))
      do idir = 1, kick%dim
        read(iunit, '(15x,99f18.12)') kick%pol(1:kick%dim, idir)
      end do
      read(iunit, '(15x,i2)')      kick%pol_dir
      read(iunit, '(15x,i2)')      kick%pol_equiv_axes
      read(iunit, '(15x,99f18.12)') kick%wprime(1:kick%dim)
    end if
    if (kick%delta_strength_mode == kick_magnon_mode) then
      read(iunit, '(15x,i3)') kick%nqvec
      safe_allocate(kick%qvector(1:3, 1:kick%nqvec))
      do im = 1, kick%nqvec
        read(iunit, '(15x,3f18.12)') kick%qvector(1:kick%dim, im)
      end do
      read(iunit, '(15x,3f18.12)')   kick%easy_axis(1:3)
      read(iunit, '(15x,3f18.12)')   kick%trans_vec(1:3,1)
      read(iunit, '(15x,3f18.12)')   kick%trans_vec(1:3,2)
    end if
    read(iunit, '(15x,f18.12)', iostat = ierr) kick%time
 
    if (ierr /= 0) then
      kick%time = m_zero
      backspace(iunit)
    end if
 
    if (kick%function_mode < 0) then
      message(1) = "No kick could be read from file."
      call messages_fatal(1, namespace=namespace)
    end if
 
    pop_sub(kick_read)
  end subroutine kick_read
 
 
  ! ---------------------------------------------------------
  subroutine kick_write(kick, iunit, out)
    type(kick_t),          intent(in)    :: kick
    integer,    optional,  intent(in)    :: iunit
    type(c_ptr), optional, intent(inout) :: out
 
    integer :: idir, im
    character(len=120) :: aux
 
    push_sub(kick_write)
 
    if (present(iunit)) then
      write(iunit, '(a15,i1)')      '# kick mode    ', kick%delta_strength_mode
      write(iunit, '(a15,f18.12)')  '# kick strength', kick%delta_strength
      write(iunit, '(a15,i2)')      '# dim          ', kick%dim
      ! if this were to be read by humans, we would want units_from_atomic(units_out%length**(-1))
      if (kick%function_mode == kick_function_user_defined) then
        write(iunit,'(a15,1x,a)')     '# User defined:', trim(kick%user_defined_function)
      elseif (kick%n_multipoles > 0) then
        write(iunit, '(a15,i3)')    '# N multipoles ', kick%n_multipoles
        do im = 1, kick%n_multipoles
          write(iunit, '(a15,2i3,f18.12)') '# multipole    ', kick%l(im), kick%m(im), kick%weight(im)
        end do
      else
        do idir = 1, kick%dim
          write(iunit, '(a6,i1,a8,99f18.12)') '# pol(', idir, ')       ', kick%pol(1:kick%dim, idir)
        end do
        write(iunit, '(a15,i1)')      '# direction    ', kick%pol_dir
        write(iunit, '(a15,i1)')      '# Equiv. axes  ', kick%pol_equiv_axes
        write(iunit, '(a15,99f18.12)') '# wprime       ', kick%wprime(1:kick%dim)
      end if
      write(iunit, '(a15,f18.12)') "# kick time    ", kick%time
 
    else if (present(out)) then
      write(aux, '(a15,i2)')      '# kick mode    ', kick%delta_strength_mode
      call write_iter_string(out, aux)
      call write_iter_nl(out)
      write(aux, '(a15,f18.12)')  '# kick strength', kick%delta_strength
      call write_iter_string(out, aux)
      call write_iter_nl(out)
      write(aux, '(a15,i2)')      '# dim          ', kick%dim
      call write_iter_string(out, aux)
      call write_iter_nl(out)
      if (kick%function_mode == kick_function_user_defined) then
        write(aux,'(a15,1x,a)')     '# User defined:', trim(kick%user_defined_function)
        call write_iter_string(out, aux)
        call write_iter_nl(out)
      elseif (kick%n_multipoles > 0) then
        write(aux, '(a15,i3)')      '# N multipoles ', kick%n_multipoles
        call write_iter_string(out, aux)
        call write_iter_nl(out)
        do im = 1, kick%n_multipoles
          write(aux, '(a15,2i3,f18.12)') '# multipole    ', kick%l(im), kick%m(im), kick%weight(im)
          call write_iter_string(out, aux)
          call write_iter_nl(out)
        end do
      else
        do idir = 1, kick%dim
          write(aux, '(a6,i1,a8,99f18.12)') '# pol(', idir, ')       ', kick%pol(1:kick%dim, idir)
          call write_iter_string(out, aux)
          call write_iter_nl(out)
        end do
        write(aux, '(a15,i2)')      '# direction    ', kick%pol_dir
        call write_iter_string(out, aux)
        call write_iter_nl(out)
        write(aux, '(a15,i2)')      '# Equiv. axes  ', kick%pol_equiv_axes
        call write_iter_string(out, aux)
        call write_iter_nl(out)
        write(aux, '(a15,99f18.12)') '# wprime       ', kick%wprime(1:kick%dim)
        call write_iter_string(out, aux)
        call write_iter_nl(out)
      end if
      if (present(out) .and. kick%delta_strength_mode == kick_magnon_mode) then
        write(aux, '(a15,i3)')      '# N q-vectors  ', kick%nqvec
        call write_iter_string(out, aux)
        call write_iter_nl(out)
        do im = 1, kick%nqvec
          write(aux, '(a15,3f18.12)') '# q-vector     ', kick%qvector(1:kick%dim, im)
          call write_iter_string(out, aux)
          call write_iter_nl(out)
        end do
        write(aux, '(a15,3f18.12)')   '# Easy axis    ', kick%easy_axis(1:3)
        call write_iter_string(out, aux)
        call write_iter_nl(out)
        write(aux, '(a15,3f18.12)')   '# Trans. dir 1 ', kick%trans_vec(1:3,1)
        call write_iter_string(out, aux)
        call write_iter_nl(out)
        write(aux, '(a15,3f18.12)')   '# Trans. dir 2 ', kick%trans_vec(1:3,2)
        call write_iter_string(out, aux)
        call write_iter_nl(out)
      end if
      write(aux, '(a15,f18.12)') "# kick time    ", kick%time
      call write_iter_string(out, aux)
      call write_iter_nl(out)
 
    end if
 
    pop_sub(kick_write)
  end subroutine kick_write
 
 
  ! ---------------------------------------------------------
  !
  subroutine kick_function_get(space, mesh, kick, kick_function, iq, to_interpolate)
    class(space_t),       intent(in)    :: space
    class(mesh_t),        intent(in)    :: mesh
    type(kick_t),         intent(in)    :: kick
    complex(real64),      intent(out)   :: kick_function(:)
    integer,              intent(in)    :: iq
    logical, optional,    intent(in)    :: to_interpolate
 
    integer :: ip, im
    real(real64)   :: xx(space%dim)
    real(real64)   :: rkick, ikick, rr, ylm
 
    integer :: np
 
    push_sub(kick_function_get)
 
    np = mesh%np
    if (present(to_interpolate)) then
      if (to_interpolate) np = mesh%np_part
    end if
 
    if (abs(kick%qlength) > m_epsilon .or. kick%delta_strength_mode == kick_magnon_mode) then ! q-vector is set
 
      select case (kick%qkick_mode)
      case (qkickmode_cos)
        write(message(1), '(a,3F9.5,a)') 'Info: Using cos(q.r) field with q = (', kick%qvector(1:3, iq), ')'
      case (qkickmode_sin)
        write(message(1), '(a,3F9.5,a)') 'Info: Using sin(q.r) field with q = (', kick%qvector(1:3, iq), ')'
      case (qkickmode_sin + qkickmode_cos)
        write(message(1), '(a,3F9.5,a)') 'Info: Using sin(q.r)+cos(q.r) field with q = (', kick%qvector(1:3, iq), ')'
      case (qkickmode_exp)
        select case(kick%dim)
        case (1)
          write(message(1), '(a,1F9.5,a)') 'Info: Using exp(iq.r) field with q = (', kick%qvector(1:kick%dim, iq), ')'
        case (2)
          write(message(1), '(a,2F9.5,a)') 'Info: Using exp(iq.r) field with q = (', kick%qvector(1:kick%dim, iq), ')'
        case (3)
          write(message(1), '(a,3F9.5,a)') 'Info: Using exp(iq.r) field with q = (', kick%qvector(1:kick%dim, iq), ')'
        end select
      case (qkickmode_bessel)
        write(message(1), '(a,I2,a,I2,a,F9.5)') 'Info: Using j_l(qr)*Y_lm(r) field with (l,m)= (', &
          kick%qbessel_l, ",", kick%qbessel_m,') and q = ', kick%qlength
      case default
        write(message(1), '(a)') 'Info: Unknown field type!'
      end select
      call messages_info(1)
 
      kick_function = m_z0
      do ip = 1, np
        xx = mesh%x(ip, :)
        select case (kick%qkick_mode)
        case (qkickmode_cos)
          kick_function(ip) = kick_function(ip) + cos(dot_product(kick%qvector(1:kick%dim, iq), xx))
        case (qkickmode_sin)
          kick_function(ip) = kick_function(ip) + sin(dot_product(kick%qvector(1:kick%dim, iq), xx))
        case (qkickmode_sin+qkickmode_cos)
          kick_function(ip) = kick_function(ip) + sin(dot_product(kick%qvector(1:kick%dim, iq), xx))
        case (qkickmode_exp)
          kick_function(ip) = kick_function(ip) + exp(m_zi * dot_product(kick%qvector(:, iq), xx))
        case (qkickmode_bessel)
          call ylmr_real(xx, kick%qbessel_l, kick%qbessel_m, ylm)
          kick_function(ip) = kick_function(ip) + loct_sph_bessel(kick%qbessel_l, kick%qlength*norm2(xx))*ylm
        end select
      end do
 
    else
      if (kick%function_mode == kick_function_user_defined) then
 
        kick_function = m_z0
        do ip = 1, np
          call mesh_r(mesh, ip, rr, coords = xx)
          rkick = m_zero
          ikick = m_zero
          call parse_expression(rkick, ikick, space%dim, xx, rr, m_zero, trim(kick%user_defined_function))
          kick_function(ip) = rkick
        end do
 
      elseif (kick%n_multipoles > 0) then
 
        kick_function = m_z0
        do im = 1, kick%n_multipoles
          do ip = 1, np
            call mesh_r(mesh, ip, rr, coords = xx)
            call loct_ylm(1, xx(1), xx(2), xx(3), kick%l(im), kick%m(im), ylm)
            kick_function(ip) = kick_function(ip) + kick%weight(im) * (rr**kick%l(im)) * ylm
          end do
        end do
      else
        do ip = 1, np
          kick_function(ip) = sum(mesh%x(ip, 1:space%dim) * &
            kick%pol(1:space%dim, kick%pol_dir))
        end do
      end if
    end if
 
    pop_sub(kick_function_get)
  end subroutine kick_function_get
 
 
  ! ---------------------------------------------------------
  !
  subroutine kick_pcm_function_get(space, mesh, kick, psolver, pcm, kick_pcm_function)
    class(space_t),       intent(in)    :: space
    class(mesh_t),        intent(in)    :: mesh
    type(kick_t),         intent(in)    :: kick
    type(poisson_t),      intent(in)    :: psolver
    type(pcm_t),          intent(inout) :: pcm
    complex(real64),      intent(out)   :: kick_pcm_function(:)
 
    complex(real64), allocatable :: kick_function_interpolate(:)
    real(real64), allocatable :: kick_function_real(:)
 
    push_sub(kick_pcm_function_get)
 
    kick_pcm_function = m_zero
    if (pcm%localf) then
      safe_allocate(kick_function_interpolate(1:mesh%np_part))
      kick_function_interpolate = m_zero
      call kick_function_get(space, mesh, kick, kick_function_interpolate, 1, to_interpolate = .true.)
      safe_allocate(kick_function_real(1:mesh%np_part))
      kick_function_real = dreal(kick_function_interpolate)
      if (pcm%kick_like) then
        ! computing kick-like polarization due to kick
        call pcm_calc_pot_rs(pcm, mesh, psolver, kick = kick%delta_strength * kick_function_real, kick_time = .true.)
      else if (.not. pcm%kick_like .and. pcm%which_eps == pcm_debye_model) then
        ! computing the kick-like part of polarization due to kick for Debye dielectric model
        pcm%kick_like = .true.
        call pcm_calc_pot_rs(pcm, mesh, psolver, kick = kick%delta_strength * kick_function_real, kick_time = .true.)
        pcm%kick_like = .false.
      else if (.not. pcm%kick_like .and. pcm%which_eps == pcm_drude_model) then
        pop_sub(kick_pcm_function_get)
        return
      end if
      kick_pcm_function = pcm%v_kick_rs / kick%delta_strength
    end if
 
    pop_sub(kick_pcm_function_get)
  end subroutine kick_pcm_function_get
 
 
  ! ---------------------------------------------------------
  subroutine kick_apply(space, mesh, st, ions_dyn, ions, kick, psolver, kpoints, pcm)
    class(space_t),        intent(in)    :: space
    class(mesh_t),         intent(in)    :: mesh
    type(states_elec_t),   intent(inout) :: st
    type(ion_dynamics_t),  intent(in)    :: ions_dyn
    type(ions_t),          intent(inout) :: ions
    type(kick_t),          intent(in)    :: kick
    type(poisson_t),       intent(in)    :: psolver
    type(kpoints_t),       intent(in)    :: kpoints
    type(pcm_t), optional, intent(inout) :: pcm
 
    integer :: iqn, ist, idim, ip, ispin, iatom
    complex(real64)   :: cc(2), kick_value
    complex(real64), allocatable :: kick_function(:), psi(:, :)
 
    complex(real64), allocatable :: kick_pcm_function(:)
    integer :: ns, iq
    real(real64) :: uvec(3), vvec(3), gvec(3, 3)
    real(real64) :: xx(space%dim), rr
 
    push_sub(kick_apply)
 
    ! The wavefunctions at time delta t read
    ! psi(delta t) = psi(t) exp(i k x)
    delta_strength: if (abs(kick%delta_strength) > m_epsilon) then
 
      safe_allocate(kick_function(1:mesh%np))
      if (kick%delta_strength_mode /= kick_magnon_mode .or. kick%nqvec == 1) then
        call kick_function_get(space, mesh, kick, kick_function, 1)
      end if
 
      ! PCM - computing polarization due to kick
      if (present(pcm)) then
        safe_allocate(kick_pcm_function(1:mesh%np))
        call kick_pcm_function_get(space, mesh, kick, psolver, pcm, kick_pcm_function)
        kick_function = kick_function + kick_pcm_function
      end if
 
      write(message(1),'(a,f11.6)') 'Info: Applying delta kick: k = ', kick%delta_strength
      select case (kick%function_mode)
      case (kick_function_dipole)
        message(2) = "Info: kick function: dipole."
      case (kick_function_multipole)
        message(2) = "Info: kick function: multipoles."
      case (kick_function_user_defined)
        message(2) = "Info: kick function: user defined function."
      end select
      select case (kick%delta_strength_mode)
      case (kick_density_mode)
        message(3) = "Info: Delta kick mode: Density mode"
      case (kick_spin_mode)
        message(3) = "Info: Delta kick mode: Spin mode"
      case (kick_spin_density_mode)
        message(3) = "Info: Delta kick mode: Density + Spin modes"
      end select
      call messages_info(3)
 
      ns = 1
      if (st%d%nspin == 2) ns = 2
 
      safe_allocate(psi(1:mesh%np, 1:st%d%dim))
 
      if (kick%delta_strength_mode /= kick_magnon_mode) then
 
        do iqn = st%d%kpt%start, st%d%kpt%end
          do ist = st%st_start, st%st_end
            call states_elec_get_state(st, mesh, ist, iqn, psi)
 
            select case (kick%delta_strength_mode)
            case (kick_density_mode)
              do idim = 1, st%d%dim
                do ip = 1, mesh%np
                  psi(ip, idim) = exp(m_zi*kick%delta_strength*kick_function(ip))*psi(ip, idim)
                end do
              end do
 
            case (kick_spin_mode)
              ispin = st%d%get_spin_index(iqn)
              do ip = 1, mesh%np
                kick_value = m_zi*kick%delta_strength*kick_function(ip)
 
                cc(1) = exp(kick_value)
                cc(2) = exp(-kick_value)
 
                select case (st%d%ispin)
                case (spin_polarized)
                  psi(ip, 1) = cc(ispin)*psi(ip, 1)
                case (spinors)
                  psi(ip, 1) = cc(1)*psi(ip, 1)
                  psi(ip, 2) = cc(2)*psi(ip, 2)
                end select
              end do
 
            case (kick_spin_density_mode)
              do ip = 1, mesh%np
                kick_value = m_zi*kick%delta_strength*kick_function(ip)
                cc(1) = exp(m_two*kick_value)
 
                select case (st%d%ispin)
                case (spin_polarized)
                  if (is_spin_up(iqn)) then
                    psi(ip, 1) = cc(1)*psi(ip, 1)
                  end if
                case (spinors)
                  psi(ip, 1) = cc(1)*psi(ip, 1)
                end select
              end do
            end select
 
            call states_elec_set_state(st, mesh, ist, iqn, psi)
 
          end do
        end do
 
      else
        assert(st%d%ispin == spinors)
 
        if (kick%nqvec == 1) then
          !The perturbation direction is defined as
          !cos(q.r)*uvec + sin(q.r)*vvec
          uvec(1:3) = kick%trans_vec(1:3,1)
          vvec(1:3) = kick%trans_vec(1:3,2)
 
          do iqn = st%d%kpt%start, st%d%kpt%end, ns
            do ist = st%st_start, st%st_end
 
              call states_elec_get_state(st, mesh, ist, iqn, psi)
 
              do ip = 1, mesh%np
 
                cc(1) = psi(ip, 1)
                cc(2) = psi(ip, 2)
 
                !First part: 1I*cos(\lambda)
                psi(ip, 1) = cos(kick%delta_strength)* cc(1)
                psi(ip, 2) = cos(kick%delta_strength)* cc(2)
 
                !We now add -i sin(\lambda) u.\sigma
                !           (u_z      u_x-i*u_y)            (v_z         v_x-i*v_y)
                ! =cos(q.r) (                  )  + sin(q.r)(                     )
                !           (u_x+i*u_y  -u_z   )            (v_x+i*v_y   -v_z     )
                psi(ip, 1) = psi(ip, 1) -m_zi*sin(kick%delta_strength)*( real(kick_function(ip), real64)  &
                  * (uvec(3)*cc(1) + (uvec(1)-m_zi*uvec(2))*cc(2)) &
                  + aimag(kick_function(ip)) * (vvec(3)*cc(1) + (vvec(1)-m_zi*vvec(2))*cc(2)))
                psi(ip, 2) = psi(ip, 2) -m_zi*sin(kick%delta_strength)*( real(kick_function(ip), real64)  &
                  * (-uvec(3)*cc(2) + (uvec(1)+m_zi*uvec(2))*cc(1)) &
                  + aimag(kick_function(ip)) * (-vvec(3)*cc(2) + (vvec(1)+m_zi*vvec(2))*cc(1)))
 
              end do
 
              call states_elec_set_state(st, mesh, ist, iqn, psi)
 
            end do
          end do
 
        else ! Multi-q kick
 
          call kpoints_to_absolute(kpoints%latt, (/m_one,m_zero,m_zero/), gvec(1:3, 1))
          call kpoints_to_absolute(kpoints%latt, (/m_zero,m_one,m_zero/), gvec(1:3, 2))
          call kpoints_to_absolute(kpoints%latt, (/m_zero,m_zero,m_one/), gvec(1:3, 3))
 
          kick_function = m_one
          do ip = 1, mesh%np
            call mesh_r(mesh, ip, rr, coords = xx)
            do iq = 1, 3
              if (kick%nqmult(iq) == 0) cycle
              if (abs(sin(m_half*sum(gvec(1:3, iq) * xx(1:3)))) <= m_epsilon) cycle
 
              kick_function(ip) = kick_function(ip)*sin(m_half*(2*kick%nqmult(iq)+1) &
                *sum(gvec(1:3, iq) * xx(1:3)))/sin(m_half*sum(gvec(1:3, iq) * xx(1:3)))
            end do
            kick_function(ip) = kick_function(ip)*kick%delta_strength
          end do
 
          do iqn = st%d%kpt%start, st%d%kpt%end, ns
            do ist = st%st_start, st%st_end
 
              call states_elec_get_state(st, mesh, ist, iqn, psi)
 
              do ip = 1, mesh%np
 
                cc(1) = psi(ip, 1)
                cc(2) = psi(ip, 2)
 
                !   (cos(F) + in_x sin(F)                   sin(F)(u_y (u_x-iu_y)/(1+u_z) - iu_z))
                ! = (                                                                            )
                !   (-sin(F)(u_y (u_x+iu_y)/(1+u_z)+iu_z)   cos(F) - in_x sin(F)                 )
 
                psi(ip, 1) = (cos(kick_function(ip))+m_zi*kick%easy_axis(1)*sin(kick_function(ip)))*cc(1) &
                  +sin(kick_function(ip))*(kick%easy_axis(2)*(kick%easy_axis(1) &
                  -m_zi*kick%easy_axis(2))/(1+kick%easy_axis(3))-m_zi*kick%easy_axis(3))*cc(2)
                psi(ip, 2) =-sin(kick_function(ip))*(kick%easy_axis(2)*(kick%easy_axis(1) &
                  +m_zi*kick%easy_axis(2))/(1+kick%easy_axis(3))+m_zi*kick%easy_axis(3))*cc(1) &
                  + (cos(kick_function(ip))-m_zi*kick%easy_axis(1)*sin(kick_function(ip)))*cc(2)
 
              end do
 
              call states_elec_set_state(st, mesh, ist, iqn, psi)
 
            end do
          end do
 
        end if
      end if
 
      safe_deallocate_a(psi)
 
      ! The nuclear velocities will be changed by
      ! Delta v_z = ( Z*e*E_0 / M) = - ( Z*k*\hbar / M)
      ! where M and Z are the ionic mass and charge, respectively.
      if (ion_dynamics_ions_move(ions_dyn)  .and. abs(kick%delta_strength) > m_epsilon) then
        if (kick%delta_strength_mode /= kick_magnon_mode) then
          do iatom = 1, ions%natoms
            ions%vel(:, iatom) = ions%vel(:, iatom) + &
              kick%delta_strength * kick%pol(1:ions%space%dim, kick%pol_dir) * &
              p_proton_charge * ions%charge(iatom) / ions%mass(iatom)
          end do
        end if
      end if
 
      safe_deallocate_a(kick_function)
    end if delta_strength
 
    pop_sub(kick_apply)
  end subroutine kick_apply
 
  pure integer function kick_get_type(kick) result(kick_type)
    type(kick_t),    intent(in) :: kick
 
    kick_type = kick%delta_strength_mode
 
  end function kick_get_type
 
end module kick_oct_m
 
!! Local Variables:
!! mode: f90
!! coding: utf-8
!! End: