electrons.F90

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!! Copyright (C) 2002-2006 M. Marques, A. Castro, A. Rubio, G. Bertsch
!! Copyright (C) 2009 X. Andrade
!! Copyright (C) 2020 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 electrons_oct_m
  use accel_oct_m
  use absorbing_boundaries_oct_m
  use algorithm_oct_m
  use algorithm_factory_oct_m
  use calc_mode_par_oct_m
  use classical_particles_oct_m
  use current_oct_m
  use current_to_mxll_field_oct_m
  use debug_oct_m
  use density_oct_m
  use dipole_oct_m
  use electron_space_oct_m
  use electrons_ground_state_oct_m
  use elf_oct_m
  use energy_calc_oct_m
  use ext_partner_list_oct_m
  use field_transfer_oct_m
  use forces_oct_m
  use gauge_field_oct_m
  use global_oct_m
  use grid_oct_m
  use minimizer_algorithm_oct_m
  use minimizer_scf_oct_m
  use hamiltonian_elec_oct_m
  use hamiltonian_elec_base_oct_m
  use interaction_enum_oct_m
  use interaction_oct_m
  use interaction_partner_oct_m
  use interaction_surrogate_oct_m
  use ion_dynamics_oct_m
  use ions_oct_m
  use kick_oct_m
  use ks_potential_oct_m
  use kpoints_oct_m
  use lalg_basic_oct_m
  use lattice_vectors_oct_m
  use lasers_oct_m
  use lda_u_oct_m
  use loct_oct_m
  use mesh_oct_m
  use messages_oct_m
  use modelmb_particles_oct_m
  use mpi_oct_m
  use multicomm_oct_m
  use mxll_e_field_to_matter_oct_m
  use mxll_b_field_to_matter_oct_m
  use mxll_vec_pot_to_matter_oct_m
  use mxll_elec_coupling_oct_m
  use namespace_oct_m
  use output_oct_m
  use output_low_oct_m
  use parser_oct_m
  use pes_oct_m
  use photons_oct_m
  use photon_mode_oct_m
  use photon_mode_mf_oct_m
  use poisson_oct_m
  use propagator_oct_m
  use propagator_base_oct_m
  use propagator_bomd_oct_m
  use propagator_aetrs_oct_m
  use propagator_elec_oct_m
  use propagator_exp_mid_oct_m
  use propagator_verlet_oct_m
  use propagation_ops_elec_oct_m
  use profiling_oct_m
  use quantity_oct_m
  use rdmft_oct_m
  use regridding_oct_m
  use scf_oct_m
  use space_oct_m
  use states_abst_oct_m
  use states_elec_oct_m
  use states_elec_dim_oct_m
  use stress_oct_m
  use sort_oct_m
  use system_oct_m
  use td_oct_m
  use td_write_oct_m
  use unit_system_oct_m
  use v_ks_oct_m
  use xc_oct_m
  use xc_f03_lib_m
  use xc_oep_oct_m
  use xc_interaction_oct_m
  use xc_oep_photon_oct_m
  use xc_functional_oct_m
 
  implicit none
 
  private
  public ::               &
    electrons_t
 
 
  type, extends(system_t) :: electrons_t
    ! Components are public by default
    type(electron_space_t)       :: space
    class(ions_t),     pointer   :: ions => null() 
    type(photons_t),   pointer   :: photons => null()
    type(grid_t)                 :: gr
    type(states_elec_t)          :: st
    type(v_ks_t)                 :: ks
    type(output_t)               :: outp
    type(multicomm_t)            :: mc
    type(hamiltonian_elec_t)     :: hm
    type(td_t)                   :: td
    type(current_t)              :: current_calculator
    type(dipole_t)               :: dipole
    type(scf_t)                  :: scf
    type(rdm_t)                  :: rdm
 
    type(kpoints_t) :: kpoints
 
    logical :: generate_epot
 
    type(states_elec_t)          :: st_copy
 
    ! At the moment this is not treated as an external potential
    class(lasers_t), pointer :: lasers => null()      
    class(gauge_field_t), pointer :: gfield => null()      
 
    ! List with all the external partners
    ! This will become a list of interactions in the future
    type(partner_list_t) :: ext_partners
 
    !TODO: have a list of self interactions
    type(xc_interaction_t), pointer   :: xc_interaction => null()
 
    logical :: ions_propagated = .false.
  contains
    procedure :: init_interaction => electrons_init_interaction
    procedure :: init_parallelization => electrons_init_parallelization
    procedure :: new_algorithm => electrons_new_algorithm
    procedure :: initialize => electrons_initialize
    procedure :: do_algorithmic_operation => electrons_do_algorithmic_operation
    procedure :: is_tolerance_reached => electrons_is_tolerance_reached
    procedure :: update_quantity => electrons_update_quantity
    procedure :: init_interaction_as_partner => electrons_init_interaction_as_partner
    procedure :: copy_quantities_to_interaction => electrons_copy_quantities_to_interaction
    procedure :: output_start => electrons_output_start
    procedure :: output_write => electrons_output_write
    procedure :: output_finish => electrons_output_finish
    procedure :: process_is_slave  => electrons_process_is_slave
    procedure :: restart_write_data => electrons_restart_write_data
    procedure :: restart_read_data => electrons_restart_read_data
    procedure :: update_kinetic_energy => electrons_update_kinetic_energy
    procedure :: algorithm_start => electrons_algorithm_start
    procedure :: ground_state_run => electrons_ground_state_run_system
    final :: electrons_finalize
  end type electrons_t
 
  interface electrons_t
    procedure electrons_constructor
  end interface electrons_t
 
contains
 
  function electrons_constructor(namespace, generate_epot) result(sys)
    class(electrons_t), pointer    :: sys
    type(namespace_t),  intent(in) :: namespace
    logical,  optional, intent(in) :: generate_epot
 
    integer :: iatom
    type(lattice_vectors_t) :: latt_inp
    logical :: has_photons
 
    push_sub_with_profile(electrons_constructor)
 
    allocate(sys)
 
    sys%namespace = namespace
 
    call messages_obsolete_variable(sys%namespace, 'SystemName')
 
    sys%space = electron_space_t(sys%namespace)
    call sys%space%write_info(sys%namespace)
    if (sys%space%has_mixed_periodicity()) then
      call messages_experimental('Support for mixed periodicity systems')
    end if
 
    sys%ions => ions_t(sys%namespace, latt_inp=latt_inp)
 
    call grid_init_stage_1(sys%gr, sys%namespace, sys%space, sys%ions%symm, latt_inp, sys%ions%natoms, sys%ions%pos)
 
    if (sys%space%is_periodic()) then
      call sys%ions%latt%write_info(sys%namespace)
    end if
 
    ! Sanity check for atomic coordinates
    do iatom = 1, sys%ions%natoms
      ! Using the same tolerance of fold_into_cell to avoid problems with mixed periodicities
      ! as the default tolerance of contains_point is too tight
      if (.not. sys%gr%box%contains_point(sys%ions%pos(:, iatom), tol=1.0e-6_real64)) then
        if (sys%space%periodic_dim /= sys%space%dim) then
          write(message(1), '(a,i5,a)') "Atom ", iatom, " is outside the box."
          call messages_warning(1, namespace=sys%namespace)
        end if
      end if
    end do
 
    ! we need k-points for periodic systems
    call kpoints_init(sys%kpoints, sys%namespace, sys%gr%symm, sys%space%dim, sys%space%periodic_dim, sys%ions%latt)
 
    call states_elec_init(sys%st, sys%namespace, sys%space, sys%ions%val_charge(), sys%kpoints)
    call sys%st%write_info(sys%namespace)
 
    ! if independent particles in N dimensions are being used, need to initialize them
    !  after masses are set to 1 in grid_init_stage_1 -> derivatives_init
    call sys%st%modelmbparticles%copy_masses(sys%gr%der%masses)
 
    call elf_init(sys%namespace)
 
    sys%generate_epot = optional_default(generate_epot, .true.)
 
    call sys%dipole%init(sys%space)
 
    sys%supported_interactions_as_partner = [current_to_mxll_field]
 
    call sys%quantities%add(quantity_t("wavefunctions", updated_on_demand = .false.))
    call sys%quantities%add(quantity_t("current", updated_on_demand = .true., parents=["wavefunctions"]))
    call sys%quantities%add(quantity_t("dipole", updated_on_demand = .true., parents=["wavefunctions"]))
    call current_init(sys%current_calculator, sys%namespace)
 
    !%Variable EnablePhotons
    !%Type logical
    !%Default no
    !%Section Hamiltonian
    !%Description
    !% This variable can be used to enable photons in several types of calculations.
    !% It can be used to activate the one-photon OEP formalism.
    !% In the case of CalculationMode = casida, it enables photon modes as
    !% described in ACS Photonics 2019, 6, 11, 2757-2778.
    !% Finally, if set to yes when solving the ferquency-dependent Sternheimer
    !% equation, the photons are coupled to the electronic subsystem.
    !%End
    call messages_obsolete_variable(namespace, 'OEPPtX', 'EnablePhotons')
    call parse_variable(namespace, 'EnablePhotons', .false., has_photons)
    if (has_photons) then
      call messages_experimental("EnablePhotons = yes")
      sys%photons => photons_t(sys%namespace)
    else
      nullify(sys%photons)
    end if
 
    pop_sub_with_profile(electrons_constructor)
  end function electrons_constructor
 
  ! ---------------------------------------------------------
  subroutine electrons_init_interaction(this, interaction)
    class(electrons_t), target, intent(inout) :: this
    class(interaction_t),       intent(inout) :: interaction
 
    real(real64) :: dmin
    integer :: rankmin, depth
    logical :: mxll_interaction_present
    logical :: calc_dipole
 
    push_sub(electrons_init_interactions)
 
    mxll_interaction_present = .false.
    select type (interaction)
    type is (mxll_e_field_to_matter_t)
      call interaction%init(this%gr, 3)
      mxll_interaction_present = .true.
      interaction%type = mxll_field_trans
    type is (mxll_b_field_to_matter_t)
      call interaction%init(this%gr, 3)
      mxll_interaction_present = .true.
    type is (mxll_vec_pot_to_matter_t)
      call interaction%init(this%gr, 3)
      mxll_interaction_present = .true.
    class default
      message(1) = "Trying to initialize an unsupported interaction by the electrons."
      call messages_fatal(1, namespace=this%namespace)
    end select
 
    if (mxll_interaction_present) then
      calc_dipole = any(this%hm%mxll%coupling_mode == &
        [velocity_gauge_dipole, length_gauge_dipole, multipolar_expansion])
 
      if (calc_dipole) then
        assert(this%space%periodic_dim == 0)
        this%hm%mxll%calc_field_dip = .true.
        this%hm%mxll%center_of_mass(1:3) = this%ions%center_of_mass()
        this%hm%mxll%center_of_mass_ip = mesh_nearest_point(this%gr, this%hm%mxll%center_of_mass, dmin, rankmin)
        this%hm%mxll%center_of_mass_rankmin = rankmin
      end if
    end if
 
    ! set interpolation depth for field-transfer interactions
    select type (interaction)
    class is (field_transfer_t)
      ! interpolation depth depends on the propagator
      select type (algo => this%algo)
      type is (propagator_exp_mid_t)
        depth = 3
      type is (propagator_aetrs_t)
        depth = 3
      type is (propagator_bomd_t)
        depth = 1
      class default
        message(1) = "The chosen algorithm does not yet support interaction interpolation"
        call messages_fatal(1, namespace=this%namespace)
      end select
 
      call interaction%init_interpolation(depth, interaction%label)
    end select
 
    pop_sub(electrons_init_interactions)
  end subroutine electrons_init_interaction
 
  ! ---------------------------------------------------------
  subroutine electrons_init_parallelization(this, grp)
    class(electrons_t), intent(inout) :: this
    type(mpi_grp_t),    intent(in)    :: grp
 
    integer(int64) :: index_range(4)
    real(real64) :: mesh_global, mesh_local, wfns
    integer :: idir
    real(real64) :: spiral_q(3), spiral_q_red(3)
    type(block_t) :: blk
 
    push_sub(electrons_init_parallelization)
 
    call mpi_grp_copy(this%grp, grp)
 
    ! store the ranges for these two indices (serves as initial guess
    ! for parallelization strategy)
    index_range(1) = this%gr%np_global  ! Number of points in mesh
    index_range(2) = this%st%nst             ! Number of states
    index_range(3) = this%st%nik           ! Number of k-points
    index_range(4) = 100000                 ! Some large number
 
    ! create index and domain communicators
    call multicomm_init(this%mc, this%namespace, this%grp, calc_mode_par, &
      mpi_world%size, index_range, (/ 5000, 1, 1, 1 /))
 
    call this%ions%partition(this%mc)
    call kpoints_distribute(this%st, this%mc)
    call states_elec_distribute_nodes(this%st, this%namespace, this%mc)
 
 
    if (parse_is_defined(this%namespace, 'TDMomentumTransfer') .or. &
      parse_is_defined(this%namespace, 'TDReducedMomentumTransfer')) then
      if (parse_block(this%namespace, 'TDMomentumTransfer', blk) == 0) then
        do idir = 1, this%space%dim
          call parse_block_float(blk, 0, idir - 1, spiral_q(idir))
        end do
      else if(parse_block(this%namespace, 'TDReducedMomentumTransfer', blk) == 0) then
        do idir = 1, this%space%dim
          call parse_block_float(blk, 0, idir - 1, spiral_q_red(idir))
        end do
        call kpoints_to_absolute(this%kpoints%latt, spiral_q_red(1:this%space%dim), spiral_q(1:this%space%dim))
      end if
      call parse_block_end(blk)
      call grid_init_stage_2(this%gr, this%namespace, this%space, this%mc, spiral_q)
    else
      call grid_init_stage_2(this%gr, this%namespace, this%space, this%mc)
    end if
 
    if (this%st%symmetrize_density) then
      call mesh_check_symmetries(this%gr, this%gr%symm, this%ions%space%periodic_dim)
    end if
 
    call output_init(this%outp, this%namespace, this%space, this%st, this%gr, this%st%nst, this%ks)
    call states_elec_densities_init(this%st, this%gr)
    call states_elec_exec_init(this%st, this%namespace, this%mc)
 
    if (associated(this%photons)) then
      this%ks%has_photons = .true.
    end if
 
    call v_ks_init(this%ks, this%namespace, this%gr, this%st, this%ions, this%mc, this%space, this%kpoints)
    if (this%ks%theory_level == kohn_sham_dft .or. this%ks%theory_level == generalized_kohn_sham_dft) then
      this%xc_interaction => xc_interaction_t(this)
    end if
 
    ! For the moment the photons are initialized here
 
    if(this%ks%has_photons) then
      this%ks%pt => this%photons%modes
      ! Temporary creation that should go in the system initialization later
      call photon_mode_set_n_electrons(this%photons%modes, this%st%qtot)
      write(message(1), '(a,i5,a)') 'Happy to have ', this%photons%modes%nmodes, ' photon modes with us.'
      call messages_info(1)
      call mf_init(this%ks%pt_mx, this%gr, this%st, this%ions, this%ks%pt)
      ! OEP for photons
      if(bitand(this%ks%xc_family, xc_family_oep) /= 0 .and. this%ks%xc%functional(func_x,1)%id == xc_oep_x) then
        this%ks%oep_photon%level = this%ks%oep%level
        call xc_oep_photon_init(this%ks%oep_photon, this%namespace, this%ks%xc_family, this%gr, this%st, this%mc, this%space)
      else
        this%ks%oep_photon%level = oep_level_none
      end if
 
    end if
 
 
    ! Temporary place for the initialization of the lasers
    this%lasers => lasers_t(this%namespace)
    call lasers_parse_external_fields(this%lasers)
    call lasers_generate_potentials(this%lasers, this%gr, this%space, this%ions%latt)
    if(this%lasers%no_lasers > 0) then
      call this%ext_partners%add(this%lasers)
      call lasers_check_symmetries(this%lasers, this%kpoints)
    else
      deallocate(this%lasers)
    end if
 
    ! Temporary place for the initialization of the gauge field
    this%gfield => gauge_field_t(this%namespace, this%ions%latt%rcell_volume)
    if(gauge_field_is_used(this%gfield)) then
      call this%ext_partners%add(this%gfield)
      call gauge_field_check_symmetries(this%gfield, this%kpoints)
    else
      deallocate(this%gfield)
    end if
 
    call hamiltonian_elec_init(this%hm, this%namespace, this%space, this%gr, this%ions, this%ext_partners, &
      this%st, this%ks%theory_level, this%ks%xc, this%mc, this%kpoints, &
      need_exchange = output_need_exchange(this%outp) .or. this%ks%oep%level /= oep_level_none, &
      xc_photons = this%ks%xc_photons )
 
    if (this%hm%pcm%run_pcm .and. this%mc%par_strategy /= p_strategy_serial .and. this%mc%par_strategy /= p_strategy_states) then
      call messages_experimental('Parallel in domain calculations with PCM')
    end if
 
    ! Print memory requirements
    call messages_print_with_emphasis(msg='Approximate memory requirements', namespace=this%namespace)
 
    mesh_global = mesh_global_memory(this%gr)
    mesh_local  = mesh_local_memory(this%gr)
 
    call messages_write('Mesh')
    call messages_new_line()
    call messages_write('  global  :')
    call messages_write(mesh_global, units = unit_megabytes, fmt = '(f10.1)')
    call messages_new_line()
    call messages_write('  local   :')
    call messages_write(mesh_local, units = unit_megabytes, fmt = '(f10.1)')
    call messages_new_line()
    call messages_write('  total   :')
    call messages_write(mesh_global + mesh_local, units = unit_megabytes, fmt = '(f10.1)')
    call messages_new_line()
    call messages_info(namespace=this%namespace)
 
    wfns = states_elec_wfns_memory(this%st, this%gr)
    call messages_write('States')
    call messages_new_line()
    call messages_write('  real    :')
    call messages_write(wfns, units = unit_megabytes, fmt = '(f10.1)')
    call messages_write(' (par_kpoints + par_states + par_domains)')
    call messages_new_line()
    call messages_write('  complex :')
    call messages_write(2.0_8*wfns, units = unit_megabytes, fmt = '(f10.1)')
    call messages_write(' (par_kpoints + par_states + par_domains)')
    call messages_new_line()
    call messages_info(namespace=this%namespace)
 
    call messages_print_with_emphasis(namespace=this%namespace)
 
    if (this%generate_epot) then
      message(1) = "Info: Generating external potential"
      call messages_info(1, namespace=this%namespace)
      call hamiltonian_elec_epot_generate(this%hm, this%namespace, this%space, this%gr, this%ions, &
        this%ext_partners, this%st)
      message(1) = "      done."
      call messages_info(1, namespace=this%namespace)
    end if
 
    if (this%ks%theory_level /= independent_particles) then
      call poisson_async_init(this%hm%psolver, this%mc)
      ! slave nodes do not call the calculation routine
      if (multicomm_is_slave(this%mc)) then
        !for the moment we only have one type of slave
        call poisson_slave_work(this%hm%psolver, this%namespace)
      end if
    end if
 
    allocate(this%supported_interactions(0))
    select case (this%hm%mxll%coupling_mode)
    case (length_gauge_dipole)
      this%supported_interactions = [this%supported_interactions, mxll_e_field_to_matter]
    case (velocity_gauge_dipole, full_minimal_coupling)
      this%supported_interactions = [this%supported_interactions, mxll_vec_pot_to_matter]
      if (this%hm%mxll%add_zeeman) then
        this%supported_interactions = [this%supported_interactions, mxll_b_field_to_matter]
      end if
    case (multipolar_expansion)
      if (this%hm%mxll%add_electric_dip .or. this%hm%mxll%add_electric_quad) then
        this%supported_interactions = [this%supported_interactions, mxll_e_field_to_matter]
      end if
      if (this%hm%mxll%add_magnetic_dip) then
        this%supported_interactions = [this%supported_interactions, mxll_b_field_to_matter]
      end if
    case (no_maxwell_coupling)
      ! Do not initialize any interaction with Maxwell
    case default
      message(1) = "Unknown maxwell-matter coupling"
      call messages_fatal(1, namespace=this%namespace)
    end select
 
    pop_sub(electrons_init_parallelization)
  end subroutine electrons_init_parallelization
 
  ! ---------------------------------------------------------
  subroutine electrons_new_algorithm(this, factory)
    class(electrons_t),         intent(inout) :: this
    class(algorithm_factory_t), intent(in)    :: factory
 
    push_sub(electrons_new_algorithm)
 
    call system_new_algorithm(this, factory)
 
    select type (algo => this%algo)
    class is (propagator_t)
 
      call td_init(this%td, this%namespace, this%space, this%gr, this%ions, this%st, this%ks, &
        this%hm, this%ext_partners, this%outp)
 
      ! this corresponds to the first part of td_init_run
      call td_allocate_wavefunctions(this%td, this%namespace, this%mc, this%gr, this%ions, this%st, &
        this%hm, this%space)
      call td_init_gaugefield(this%td, this%namespace, this%gr, this%st, this%ks, this%hm, &
        this%ext_partners, this%space)
 
    class is (minimizer_algorithm_t)
 
      call electrons_gs_allocate_wavefunctions(this%namespace, this%gr, this%st, this%hm, this%scf, this%ks, &
        this%ions, this%mc, this%space)
 
    class default
      assert(.false.)
    end select
 
    pop_sub(electrons_new_algorithm)
  end subroutine electrons_new_algorithm
 
  ! ---------------------------------------------------------
  subroutine electrons_initialize(this)
    class(electrons_t), intent(inout) :: this
 
    push_sub(electrons_initialize)
 
    select type (algo => this%algo)
    class is (propagator_t)
      call td_set_from_scratch(this%td, .true.)
      call td_load_restart_from_gs(this%td, this%namespace, this%space, this%mc, this%gr, &
        this%ext_partners, this%st, this%ks, this%hm)
 
    class is (minimizer_algorithm_t)
 
      call electrons_gs_initialize(this%namespace, this%scf, this%rdm, this%gr, this%mc, this%st, &
        this%hm, this%ions, this%ks, this%space, this%ext_partners, fromscratch=.true.)
    class default
      assert(.false.)
    end select
 
    pop_sub(electrons_initialize)
  end subroutine electrons_initialize
 
  ! ---------------------------------------------------------
  subroutine electrons_algorithm_start(this)
    class(electrons_t),      intent(inout) :: this
 
    push_sub(electrons_algorithm_start)
 
    call system_algorithm_start(this)
 
    select type (algo => this%algo)
    class is (propagator_t)
 
      ! additional initialization needed for electrons
      call td_init_with_wavefunctions(this%td, this%namespace, this%space, this%mc, this%gr, this%ions, &
        this%ext_partners, this%st, this%ks, this%hm, this%outp, td_get_from_scratch(this%td))
 
    end select
 
    pop_sub(electrons_algorithm_start)
  end subroutine electrons_algorithm_start
 
  ! ---------------------------------------------------------
  logical function electrons_do_algorithmic_operation(this, operation, updated_quantities) result(done)
    class(electrons_t),             intent(inout) :: this
    class(algorithmic_operation_t), intent(in)    :: operation
    character(len=:), allocatable,  intent(out)   :: updated_quantities(:)
 
    logical :: update_energy_
    type(gauge_field_t), pointer :: gfield
    real(real64) :: time
    integer :: iter
 
    push_sub(electrons_do_algorithmic_operation)
    call profiling_in(trim(this%namespace%get())//":"//trim(operation%id))
 
    update_energy_ = .true.
 
    ! kick at t > 0 still missing!
 
    done = .true.
    select type (algo => this%algo)
    class is (propagator_t)
      time = algo%iteration%value()
      select case (operation%id)
      case (aetrs_first_half)
        ! propagate half of the time step with H(time)
        call get_fields_from_interaction(this, time)
        call propagation_ops_elec_update_hamiltonian(this%namespace, this%space, this%st, this%gr, &
          this%hm, this%ext_partners, time)
        call propagation_ops_elec_exp_apply(this%td%tr%te, this%namespace, this%st, this%gr, this%hm, m_half*algo%dt)
 
      case (aetrs_extrapolate)
        ! Do the extrapolation of the Hamiltonian
        ! First the extrapolation of the potential
        call this%hm%ks_pot%interpolation_new(this%td%tr%vks_old, time+algo%dt, algo%dt)
 
        !Get the potentials from the interpolator
        call propagation_ops_elec_interpolate_get(this%hm, this%gr, this%td%tr%vks_old)
 
        ! Second the ions and gauge field which later on will be treated as extrapolation
        ! of interactions, but this is not yet possible
 
        ! move the ions to time t
        call propagation_ops_elec_move_ions(this%td%tr%propagation_ops_elec, this%gr, this%hm, &
          this%st, this%namespace, this%space, this%td%ions_dyn, this%ions, this%ext_partners, &
          this%mc, time+algo%dt, algo%dt)
 
        !Propagate gauge field
        gfield => list_get_gauge_field(this%ext_partners)
        if(associated(gfield)) then
          call propagation_ops_elec_propagate_gauge_field(this%td%tr%propagation_ops_elec, gfield, &
            algo%dt, time+algo%dt)
        end if
 
        !Update Hamiltonian and current
        call get_fields_from_interaction(this, time+algo%dt)
        call propagation_ops_elec_update_hamiltonian(this%namespace, this%space, this%st, this%gr, &
          this%hm, this%ext_partners, time+algo%dt)
 
      case (aetrs_second_half)
        !Do the time propagation for the second half of the time step
        call propagation_ops_elec_fuse_density_exp_apply(this%td%tr%te, this%namespace, this%st, &
          this%gr, this%hm, m_half*algo%dt)
 
        updated_quantities = ["wavefunctions"]
 
      case (expmid_extrapolate)
        ! the half step of this propagator screws with the gauge field kick
        gfield => list_get_gauge_field(this%ext_partners)
        if(associated(gfield)) then
          assert(gauge_field_is_propagated(gfield) .eqv. .false.)
        end if
 
        ! Do the extrapolation of the Hamiltonian
        ! First the extrapolation of the potential
        call this%hm%ks_pot%interpolation_new(this%td%tr%vks_old, time+algo%dt, algo%dt)
 
        ! get the potentials from the interpolator
        call this%hm%ks_pot%interpolate_potentials(this%td%tr%vks_old, 3, time+algo%dt, algo%dt, time + algo%dt/m_two)
 
        ! Second the ions which later on will be treated as extrapolation of interactions,
        ! but this is not yet possible
        ! move the ions to the half step
        call propagation_ops_elec_move_ions(this%td%tr%propagation_ops_elec, this%gr, this%hm, this%st, &
          this%namespace, this%space, this%td%ions_dyn, this%ions, this%ext_partners, &
          this%mc, time + m_half*algo%dt, m_half*algo%dt, save_pos=.true.)
 
        call get_fields_from_interaction(this, time + m_half*algo%dt)
        call propagation_ops_elec_update_hamiltonian(this%namespace, this%space, this%st, this%gr, &
          this%hm, this%ext_partners, time + m_half*algo%dt)
 
      case (expmid_propagate)
        ! Do the actual propagation step
        call propagation_ops_elec_fuse_density_exp_apply(this%td%tr%te, this%namespace, this%st, &
          this%gr, this%hm, algo%dt)
 
        ! restore to previous time
        call propagation_ops_elec_restore_ions(this%td%tr%propagation_ops_elec, this%td%ions_dyn, this%ions)
 
        updated_quantities = ["wavefunctions"]
 
      case (bomd_start)
        call scf_init(this%scf, this%namespace, this%gr, this%ions, this%st, this%mc, this%hm, this%space)
        ! the ions are propagated inside the propagation step already, so no need to do it at the end
        this%ions_propagated = .true.
 
      case (verlet_update_pos)
        ! move the ions to time t
        call propagation_ops_elec_propagate_ions_and_cell(this%gr, this%hm, this%st, this%namespace, this%space, &
          this%td%ions_dyn, this%ions, this%mc, time+algo%dt, algo%dt)
 
      case (bomd_elec_scf)
        call hamiltonian_elec_epot_generate(this%hm, this%namespace, this%space, this%gr, this%ions, &
          this%ext_partners, this%st, time = time+algo%dt)
        ! now calculate the eigenfunctions
        call scf_run(this%scf, this%namespace, this%space, this%mc, this%gr, this%ions, &
          this%ext_partners, this%st, this%ks, this%hm, verbosity = verb_compact)
        ! TODO: Check if this call is realy needed. - NTD
        call hamiltonian_elec_epot_generate(this%hm, this%namespace, this%space, this%gr, this%ions, &
          this%ext_partners, this%st, time = time+algo%dt)
 
        ! update Hamiltonian and eigenvalues (fermi is *not* called)
        call v_ks_calc(this%ks, this%namespace, this%space, this%hm, this%st, this%ions, this%ext_partners, &
          calc_eigenval = .true., time = time+algo%dt, calc_energy = .true.)
 
        ! Get the energies.
        call energy_calc_total(this%namespace, this%space, this%hm, this%gr, this%st, this%ext_partners, iunit = -1)
 
        updated_quantities = ["wavefunctions"]
 
      case (verlet_compute_acc)
        ! Do nothing, forces are computing in scf_run
        if (this%td%ions_dyn%cell_relax()) then
          assert(this%scf%calc_stress)
          call this%td%ions_dyn%update_stress(this%ions%space, this%st%stress_tensors%total, &
            this%ions%latt%rlattice, this%ions%latt%rcell_volume)
        end if
 
      case (verlet_compute_vel)
        call ion_dynamics_propagate_vel(this%td%ions_dyn, this%ions)
        ! TODO: Check if this call is realy needed. - NTD
        call hamiltonian_elec_epot_generate(this%hm, this%namespace, this%space, this%gr, this%ions, &
          this%ext_partners, this%st, time = time+algo%dt)
        call this%ions%update_kinetic_energy()
 
      case (expmid_start)
        this%ions_propagated = .false.
 
      case (aetrs_start)
        ! the ions are propagated inside the propagation step already, so no need to do it at the end
        this%ions_propagated = .true.
 
      case (iteration_done)
        call electrons_exec_end_of_timestep_tasks(this, algo)
        done = .false.
 
      case (bomd_finish)
        call scf_end(this%scf)
 
      case (expmid_finish, aetrs_finish)
      case default
        done = .false.
      end select
 
    class is(minimizer_algorithm_t)
 
      ! Clocks starts at 0....
      iter = nint(this%iteration%value()) + 1
 
      select case(operation%id)
      case (gs_scf_start)
        call scf_start(this%scf, this%namespace, this%space, this%gr, this%ions, this%st, this%ks, &
          this%hm, this%outp)
 
      case (gs_scf_iteration)
 
        call scf_iter(this%scf, this%namespace, this%space, this%mc, this%gr, this%ions, &
          this%ext_partners, this%st, this%ks, this%hm, iter, outp = this%outp, &
          restart_dump=this%scf%restart_dump)
 
        algo%converged = scf_iter_finish(this%scf, this%namespace, this%space, this%gr, this%ions,&
          this%st, this%ks, this%hm, iter, outp = this%outp)
 
        updated_quantities = ["wavefunctions"]
 
      case (gs_scf_finish)
 
        ! Here iteration is iter-1, as the clock ticked before SCF_FINISH
        call scf_finish(this%scf, this%namespace, this%space, this%mc, this%gr, this%ions, &
          this%ext_partners, this%st, this%ks, this%hm, iter-1, &
          outp = this%outp, restart_dump=this%scf%restart_dump)
 
      case default
        done = .false.
      end select
    class default
      done = .false.
    end select
 
    call profiling_out(trim(this%namespace%get())//":"//trim(operation%id))
    pop_sub(electrons_do_algorithmic_operation)
  end function electrons_do_algorithmic_operation
 
  ! ---------------------------------------------------------
  logical function electrons_is_tolerance_reached(this, tol) result(converged)
    class(electrons_t), intent(in) :: this
    real(real64),       intent(in) :: tol
 
    push_sub(electrons_is_tolerance_reached)
 
    converged = .false.
 
    pop_sub(electrons_is_tolerance_reached)
  end function electrons_is_tolerance_reached
 
  ! ---------------------------------------------------------
  subroutine electrons_update_quantity(this, label)
    class(electrons_t),   intent(inout) :: this
    character(len=*),     intent(in)    :: label
 
    class(quantity_t), pointer :: quantity
 
    push_sub(electrons_update_quantity)
    call profiling_in(trim(this%namespace%get())//":"//"UPDATE_QUANTITY")
 
    quantity => this%quantities%get(label)
    if(associated(quantity)) then
      assert(quantity%updated_on_demand)
    endif
 
    select case (label)
    case ("current")
      call states_elec_allocate_current(this%st, this%space, this%gr)
      call current_calculate(this%current_calculator, this%namespace, this%gr, &
        this%hm, this%space, this%st)
    case ("dipole")
      call this%dipole%calculate(this%gr, this%ions, this%st)
    case default
      message(1) = "Incompatible quantity: "//trim(label)//"."
      call messages_fatal(1, namespace=this%namespace)
    end select
 
    call profiling_out(trim(this%namespace%get())//":"//"UPDATE_QUANTITY")
    pop_sub(electrons_update_quantity)
  end subroutine electrons_update_quantity
 
  ! ---------------------------------------------------------
  subroutine electrons_init_interaction_as_partner(partner, interaction)
    class(electrons_t),   intent(in)    :: partner
    class(interaction_surrogate_t), intent(inout) :: interaction
 
    push_sub(electrons_init_interaction_as_partner)
 
    select type (interaction)
    type is (current_to_mxll_field_t)
      call interaction%init_from_partner(partner%gr, partner%space, partner%namespace)
    class default
      message(1) = "Unsupported interaction."
      call messages_fatal(1, namespace=partner%namespace)
    end select
 
    pop_sub(electrons_init_interaction_as_partner)
  end subroutine electrons_init_interaction_as_partner
 
  ! ---------------------------------------------------------
  subroutine electrons_copy_quantities_to_interaction(partner, interaction)
    class(electrons_t),   intent(inout) :: partner
    class(interaction_surrogate_t), intent(inout) :: interaction
 
    push_sub(electrons_copy_quantities_to_interaction)
    call profiling_in(trim(partner%namespace%get())//":"//"COPY_QUANTITY_INTER")
 
    select type (interaction)
    type is (current_to_mxll_field_t)
      assert(allocated(partner%st%current))
      interaction%partner_field(:,:) = partner%st%current(1:partner%gr%np,:,1)
      call interaction%do_mapping()
    class default
      message(1) = "Unsupported interaction."
      call messages_fatal(1, namespace=partner%namespace)
    end select
 
    call profiling_out(trim(partner%namespace%get())//":"//"COPY_QUANTITY_INTER")
    pop_sub(electrons_copy_quantities_to_interaction)
  end subroutine electrons_copy_quantities_to_interaction
 
  ! ---------------------------------------------------------
  subroutine electrons_output_start(this)
    class(electrons_t), intent(inout) :: this
 
    push_sub(electrons_output_start)
 
    pop_sub(electrons_output_start)
  end subroutine electrons_output_start
 
  ! ---------------------------------------------------------
  subroutine electrons_output_write(this)
    class(electrons_t), intent(inout) :: this
 
    integer :: iter
 
    push_sub(electrons_output_write)
    call profiling_in(trim(this%namespace%get())//":"//"OUTPUT_WRITE")
 
    select type (algo => this%algo)
    class is (propagator_t)
      iter = this%iteration%counter()
 
      call td_write_iter(this%td%write_handler, this%namespace, this%space, this%outp, this%gr, &
        this%st, this%hm, this%ions, this%ext_partners, this%hm%kick, this%ks, algo%dt, iter, this%mc, this%td%recalculate_gs)
 
      if (this%outp%anything_now(iter)) then ! output
        call td_write_output(this%namespace, this%space, this%gr, this%st, this%hm, this%ks, &
          this%outp, this%ions, this%ext_partners, iter, algo%dt)
      end if
    end select
 
    call profiling_out(trim(this%namespace%get())//":"//"OUTPUT_WRITE")
    pop_sub(electrons_output_write)
  end subroutine electrons_output_write
 
  ! ---------------------------------------------------------
  subroutine electrons_output_finish(this)
    class(electrons_t), intent(inout) :: this
 
    push_sub(electrons_output_finish)
 
    pop_sub(electrons_output_finish)
  end subroutine electrons_output_finish
 
  ! ---------------------------------------------------------
  logical function electrons_process_is_slave(this) result(is_slave)
    class(electrons_t), intent(in) :: this
 
    push_sub(electrons_process_is_slave)
 
    is_slave = multicomm_is_slave(this%mc)
 
    pop_sub(electrons_process_is_slave)
  end function electrons_process_is_slave
 
  ! ---------------------------------------------------------
  subroutine electrons_exec_end_of_timestep_tasks(this, prop)
    class(electrons_t), intent(inout) :: this
    class(propagator_t), intent(in)   :: prop
 
    logical :: stopping
    logical :: generate
    logical :: update_energy_
    integer :: nt
    real(real64) :: time
    type(gauge_field_t), pointer :: gfield
 
    push_sub(electrons_exec_end_of_timestep_tasks)
    call profiling_in(trim(this%namespace%get())//":"//"END_OF_TIMESTEP")
 
    stopping = .false.
 
    nt = this%td%iter
    ! this is the time at the end of the timestep, as required in all routines here
    time = prop%dt*nt
    update_energy_ = .true.
 
    !Apply mask absorbing boundaries
    if (this%hm%abs_boundaries%abtype == mask_absorbing) call zvmask(this%gr, this%hm, this%st)
 
    !Photoelectron stuff
    if (this%td%pesv%calc_spm .or. this%td%pesv%calc_mask .or. this%td%pesv%calc_flux) then
      call pes_calc(this%td%pesv, this%namespace, this%space, this%gr, this%st, &
        prop%dt, nt, this%gr%der, this%hm%kpoints, this%ext_partners, stopping)
    end if
 
    ! For BOMD, we do not want the lines below to be executed
    select type(prop)
    type is(propagator_bomd_t)
      call profiling_out(trim(this%namespace%get())//":"//"END_OF_TIMESTEP")
      pop_sub(electrons_exec_end_of_timestep_tasks)
      return
    end select
 
    ! The propagation of the ions and the gauge field is currently done here.
    ! TODO: this code is to be moved to their own systems at some point
    generate = .false.
    if (this%td%ions_dyn%is_active()) then
      if (.not. this%ions_propagated) then
        call propagation_ops_elec_propagate_ions_and_cell(this%gr, this%hm, this%st, this%namespace, this%space, &
          this%td%ions_dyn, this%ions, this%mc, abs(nt*prop%dt), this%td%ions_dyn%ionic_scale*prop%dt)
        generate = .true.
      end if
    end if
 
    gfield => list_get_gauge_field(this%ext_partners)
    if(associated(gfield)) then
      if (gauge_field_is_propagated(gfield) .and. .not. this%ions_propagated) then
        call gauge_field_do_algorithmic_operation(gfield, op_verlet_compute_acc, prop%dt, time)
      end if
    end if
 
    if (generate .or. this%ions%has_time_dependent_species()) then
      call hamiltonian_elec_epot_generate(this%hm, this%namespace, this%space, this%gr, this%ions, &
        this%ext_partners, this%st, time = abs(nt*prop%dt))
    end if
 
    call v_ks_calc(this%ks, this%namespace, this%space, this%hm, this%st, this%ions, this%ext_partners, &
      calc_eigenval = update_energy_, time = abs(nt*prop%dt), calc_energy = update_energy_)
 
    if (update_energy_) then
      call energy_calc_total(this%namespace, this%space, this%hm, this%gr, this%st, this%ext_partners, iunit = -1)
    end if
 
    ! Recalculate forces, update velocities...
    if (this%td%ions_dyn%ions_move() .or. this%outp%what(option__output__forces) &
      .or. this%td%write_handler%out(out_separate_forces)%write) then
      call forces_calculate(this%gr, this%namespace, this%ions, this%hm, this%ext_partners, &
        this%st, this%ks, t = abs(nt*prop%dt), dt = prop%dt)
    end if
 
    if (this%td%ions_dyn%cell_relax() .or. this%outp%what(option__output__stress)) then
      call stress_calculate(this%namespace, this%gr, this%hm, this%st, this%ions, this%ks, this%ext_partners)
    end if
 
    if(this%td%ions_dyn%is_active()) then
      call ion_dynamics_propagate_vel(this%td%ions_dyn, this%ions, atoms_moved = generate)
      call this%ions%update_kinetic_energy()
    end if
 
    if(associated(gfield)) then
      if(gauge_field_is_propagated(gfield)) then
        if(abs(this%ks%xc%kernel_lrc_alpha)>m_epsilon) then
          call gauge_field_get_force(gfield, this%gr, this%st%d%spin_channels, this%st%current, &
            this%ks%xc%kernel_lrc_alpha, this%ks%xc%kernel_proca_a_zero, this%ks%xc%kernel_proca_a_one)
        else
          call gauge_field_get_force(gfield, this%gr, this%st%d%spin_channels, this%st%current)
        endif
        call gauge_field_do_algorithmic_operation(gfield, op_verlet_compute_vel, prop%dt, time)
      end if
    end if
 
    !We update the occupation matrices
    call lda_u_update_occ_matrices(this%hm%lda_u, this%namespace, this%gr, this%st, this%hm%hm_base, this%hm%phase, this%hm%energy)
 
    ! this is needed to be compatible with the code in td_*
    this%td%iter = this%td%iter + 1
 
    call profiling_out(trim(this%namespace%get())//":"//"END_OF_TIMESTEP")
    pop_sub(electrons_exec_end_of_timestep_tasks)
  end subroutine electrons_exec_end_of_timestep_tasks
 
  ! ---------------------------------------------------------
  subroutine electrons_restart_write_data(this)
    class(electrons_t), intent(inout) :: this
 
    integer :: ierr
 
    push_sub(electrons_restart_write_data)
    call profiling_in(trim(this%namespace%get())//":"//"RESTART_WRITE")
 
    select type (algo => this%algo)
    class is (propagator_t)
      call td_write_data(this%td%write_handler)
      call td_dump(this%td, this%namespace, this%space, this%gr, this%st, this%hm, &
        this%ks, this%ext_partners, this%iteration%counter(), ierr)
      if (ierr /= 0) then
        message(1) = "Unable to write time-dependent restart information."
        call messages_warning(1, namespace=this%namespace)
      end if
 
      ! TODO: this is here because of legacy reasons and should be moved to the output framework
      call pes_output(this%td%pesv, this%namespace, this%space, this%gr, this%st, this%iteration%counter(), &
        this%outp, algo%dt, this%ions)
    end select
 
    call profiling_out(trim(this%namespace%get())//":"//"RESTART_WRITE")
    pop_sub(electrons_restart_write_data)
  end subroutine electrons_restart_write_data
 
  ! ---------------------------------------------------------
  ! this function returns true if restart data could be read
  logical function electrons_restart_read_data(this)
    class(electrons_t), intent(inout) :: this
 
    logical :: from_scratch
 
    push_sub(electrons_restart_read_data)
    call profiling_in(trim(this%namespace%get())//":"//"RESTART_READ")
 
    select type (algo => this%algo)
    class is (propagator_t)
      from_scratch = .false.
      call td_load_restart_from_td(this%td, this%namespace, this%space, this%mc, this%gr, &
        this%ext_partners, this%st, this%ks, this%hm, from_scratch)
      call td_set_from_scratch(this%td, from_scratch)
 
    class is (minimizer_algorithm_t)
      from_scratch = .false.
      call electrons_gs_load_from_restart(this%namespace, this%scf, this%gr, this%mc, this%st, this%hm, &
        this%ks, this%space, this%ions, this%ext_partners,from_scratch)
 
      ! electrons_gs_initialize still knows about fromScratch.
      assert(.false.)
    end select
 
    if (from_scratch) then
      ! restart data could not be loaded
      electrons_restart_read_data = .false.
    else
      ! restart data could be loaded
      electrons_restart_read_data = .true.
    end if
 
    call profiling_out(trim(this%namespace%get())//":"//"RESTART_READ")
    pop_sub(electrons_restart_read_data)
  end function electrons_restart_read_data
 
  !----------------------------------------------------------
  subroutine electrons_update_kinetic_energy(this)
    class(electrons_t), intent(inout) :: this
 
    push_sub(electrons_update_kinetic_energy)
 
    if (states_are_real(this%st)) then
      this%kinetic_energy = denergy_calc_electronic(this%namespace, this%hm, this%gr%der, this%st, terms = term_kinetic)
    else
      this%kinetic_energy = zenergy_calc_electronic(this%namespace, this%hm, this%gr%der, this%st, terms = term_kinetic)
    end if
 
    pop_sub(electrons_update_kinetic_energy)
 
  end subroutine electrons_update_kinetic_energy
 
  ! ---------------------------------------------------------
  subroutine get_fields_from_interaction(this, time)
    class(electrons_t), intent(inout) :: this
    real(real64),       intent(in)    :: time
 
    type(interaction_iterator_t) :: iter
    real(real64), allocatable :: field_tmp(:, :)
 
    push_sub(get_fields_from_interaction)
 
    if (this%hm%mxll%coupling_mode == no_maxwell_coupling) then
      pop_sub(get_fields_from_interaction)
      return
    end if
 
    safe_allocate(field_tmp(1:this%gr%np, 1:this%gr%box%dim))
    this%hm%mxll%e_field = m_zero
    this%hm%mxll%b_field = m_zero
    this%hm%mxll%vec_pot = m_zero
 
    ! interpolate field from interaction
    call iter%start(this%interactions)
    do while (iter%has_next())
      select type (interaction => iter%get_next())
      class is (mxll_e_field_to_matter_t)
        call interaction%interpolate(time, field_tmp)
        call lalg_axpy(this%gr%np, 3, m_one, field_tmp, this%hm%mxll%e_field)
      class is (mxll_vec_pot_to_matter_t)
        call interaction%interpolate(time, field_tmp)
        call lalg_axpy(this%gr%np, 3, m_one, field_tmp, this%hm%mxll%vec_pot)
      class is (mxll_b_field_to_matter_t)
        call interaction%interpolate(time, field_tmp)
        call lalg_axpy(this%gr%np, 3, m_one, field_tmp, this%hm%mxll%b_field)
      end select
    end do
 
    safe_deallocate_a(field_tmp)
    pop_sub(get_fields_from_interaction)
 
  end subroutine get_fields_from_interaction
 
 
  subroutine electrons_ground_state_run_system(sys, from_scratch)
    class(electrons_t), intent(inout) :: sys
    logical,            intent(inout) :: from_scratch
 
    push_sub(electrons_ground_state_run_system)
 
    call electrons_ground_state_run(sys%namespace, sys%mc, sys%gr, sys%ions, &
      sys%ext_partners, sys%st, sys%ks, sys%hm, sys%outp, sys%space, from_scratch)
 
    pop_sub(electrons_ground_state_run_system)
 
  end subroutine electrons_ground_state_run_system
 
 
  subroutine electrons_finalize(sys)
    type(electrons_t), intent(inout) :: sys
 
    type(partner_iterator_t) :: iter
    class(interaction_partner_t), pointer :: partner
 
    push_sub(electrons_finalize)
 
    if (associated(sys%algo)) then
      select type (algo => sys%algo)
      class is (propagator_t)
        call td_end_run(sys%td, sys%st, sys%hm)
        call td_end(sys%td)
      class is(minimizer_algorithm_t)
        call electrons_gs_cleanup(sys%ks, sys%scf, sys%rdm, sys%st, sys%hm)
      end select
    end if
 
    if (sys%ks%theory_level /= independent_particles) then
      call poisson_async_end(sys%hm%psolver, sys%mc)
    end if
 
    call iter%start(sys%ext_partners)
    do while (iter%has_next())
      partner => iter%get_next()
      safe_deallocate_p(partner)
    end do
    call sys%ext_partners%empty()
 
    safe_deallocate_p(sys%xc_interaction)
 
    call hamiltonian_elec_end(sys%hm)
 
    nullify(sys%gfield)
    nullify(sys%lasers)
 
    call multicomm_end(sys%mc)
 
    call xc_oep_photon_end(sys%ks%oep_photon)
    if (sys%ks%has_photons) then
      call mf_end(sys%ks%pt_mx)
    end if
 
    call sys%dipole%end()
 
    call v_ks_end(sys%ks)
 
    call states_elec_end(sys%st)
 
    deallocate(sys%ions)
    safe_deallocate_p(sys%photons)
 
    call kpoints_end(sys%kpoints)
 
    call grid_end(sys%gr)
 
    call system_end(sys)
 
    pop_sub(electrons_finalize)
  end subroutine electrons_finalize
 
 
end module electrons_oct_m
 
!! Local Variables:
!! mode: f90
!! coding: utf-8
!! End: