xc_lrc.F90

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!! Copyright (C) 2002-2006 M. Marques, A. Castro, A. Rubio, G. Bertsch
!! Copyright (C) 2025 N. Tancogne-Dejean
!!
!! 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 xc_lrc_oct_m
  use debug_oct_m
  use global_oct_m
  use messages_oct_m
  use namespace_oct_m
  use parser_oct_m
  use profiling_oct_m
 
  implicit none
 
  private
  public ::             &
    xc_lrc_t,           &
    xc_lrc_init
 
  type xc_lrc_t
    private
    real(real64),          public :: alpha
    real(real64),          public :: proca_a_zero
    real(real64),          public :: proca_a_one
  end type xc_lrc_t
 
contains
 
  subroutine xc_lrc_init(this, namespace, dim, periodic_dim)
    type(xc_lrc_t),    intent(out) :: this
    type(namespace_t), intent(in)  :: namespace
    integer,           intent(in)  :: dim, periodic_dim
 
    push_sub(xc_lrc_init)
 
    !%Variable XCKernelLRCAlpha
    !%Type float
    !%Default 0.0
    !%Section Hamiltonian::XC
    !%Description
    !% Set to a non-zero value to add a long-range correction for solids to the kernel.
    !% This is the <math>\alpha</math> parameter defined in S. Botti <i>et al.</i>, <i>Phys. Rev. B</i>
    !% 69, 155112 (2004). The <math>G = G^\prime = 0</math> term <math>-\alpha/q^2</math> is taken
    !% into account by introducing an additional pole to the polarizability (see R. Stubner
    !% <i>et al.</i>, <i>Phys. Rev. B</i> 70, 245119 (2004)). The rest of the terms are included by
    !% multiplying the Hartree term by <math>1 - \alpha / 4 \pi</math>. The use of non-zero
    !% <math>\alpha</math> in combination with <tt>HamiltonianVariation</tt> = <tt>V_ext_only</tt>
    !% corresponds to account of only the <math>G = G^\prime = 0</math> term.
    !% Applicable only to isotropic systems. (Experimental)
    !%End
 
    call parse_variable(namespace, 'XCKernelLRCAlpha', m_zero, this%alpha)
    if (abs(this%alpha) > m_epsilon) then
      call messages_experimental("Long-range correction to kernel", namespace=namespace)
 
      if (periodic_dim < dim) then
        message(1) = 'The use of the LRC kernel for non-periodic dimensions makes no sense.'
        call messages_warning(1, namespace=namespace)
      end if
 
      !%Variable XCProcaResonantTerm
      !%Type float
      !%Default 0.0
      !%Section Hamiltonian :: XC
      !%Description
      !% This variable is the a_0 parameter in the Proca equation
      !% Set to a nonzero value to give to the Maxwell equation a linear term correction as suggested in
      !% J. K. Dewhurst <i>et al.</i>, <i>Phys. Rev. B</i> 111, L060302 (2025).
      !%End
      call parse_variable(namespace, 'XCProcaResonantTerm', m_zero, this%proca_a_zero)
 
      !%Variable XCProcaDamping
      !%Type float
      !%Default 0.0
      !%Section Hamiltonian :: XC
      !%Description
      !% This variable is the a_1 parameter in the Proca equation
      !% Set to a nonzero value to give to the Maxwell equation a first-order derivative term correction as suggested in
      !% J. K. Dewhurst <i>et al.</i>, <i>Phys. Rev. B</i> 111, L060302 (2025).
      !%End
      call parse_variable(namespace, 'XCProcaDamping', m_zero, this%proca_a_one)
      if (abs(this%proca_a_zero) > m_epsilon .or. abs(this%proca_a_one) > m_epsilon) then
        call messages_experimental("Proca equation", namespace=namespace)
      end if
    end if
 
    pop_sub(xc_lrc_init)
  end subroutine xc_lrc_init
 
end module xc_lrc_oct_m
 
!! Local Variables:
!! mode: f90
!! coding: utf-8
!! End: