!-*- mode: F90 -*-!
!------------------------------------------------------------!
! Copyright (C) 2026 Wannier Developer Group                 !
!                                                            !
! This library is free software; you can redistribute it     !
! and/or modify it under the terms of the GNU Lesser General !
! Public License as published by the Free Software           !
! Foundation; either version 2.1 of the License, or (at your !
! option) any later version.                                 !
!                                                            !
! This library 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 Lesser General Public License for    !
! more details.                                              !
!                                                            !
! You should have received a copy of the GNU Lesser General  !
! Public License along with this library; if not, see        !
! <https://www.gnu.org/licenses/>.                           !
!                                                            !
! The webpage of the Wannier90 code is                       !
! <https://www.wannier.org>.                                 !
!                                                            !
! The Wannier90 code is hosted on GitHub                     !
! <https://github.com/wannier-developers/wannier90>          !
!------------------------------------------------------------!
!                                                            !
!  w90_constants: physical constants and tolerances          !
!                                                            !
!------------------------------------------------------------!

module w90_constants

  !! This module contains the definitions of constants
  !! used in Wannier90 - both numerical constants such as pi
  !! and numerical convergence tolerances, but also physical
  !! constant such as the speed of light
  !!
  !! Values of the fundamental constants are taken from
  !! http://physics.nist.gov/cuu/Constants/index.html
  !! By default CODATA2022 is used (CODATA2006/10/18 can be selected
  !! using an appropriate compile-time flag (see README.install guide)

  implicit none

  private

  !~~ GENERIC CONSTANTS ~~!
  integer, parameter, public          :: i64 = selected_int_kind(15)
  !! 64bit integer
!aam_2012-04-11; fix to run on MacBook Air
  integer, parameter, public          :: dp = kind(1.0d0)
  !! double precision
  real(kind=dp), parameter, public    :: pi = 3.141592653589793238462643383279_dp
  !! $$\pi$$
  real(kind=dp), parameter, public    :: twopi = 2*pi
  !! $$2\pi$$
  complex(kind=dp), parameter, public :: cmplx_i = (0.0_dp, 1.0_dp)
  !! i as a complex variable
  complex(kind=dp), parameter, public :: cmplx_0 = (0.0_dp, 0.0_dp)
  !! 0 as a complex variable
  complex(kind=dp), parameter, public :: cmplx_1 = (1.0_dp, 0.0_dp)
  !! 1 as a complex variable

  integer, parameter, public :: maxlen = 255                     !! Max column width of input file

  !~~ NUMERICAL CONVERGENCE CONSTANTS ~~!
  real(kind=dp), parameter, public    :: eps2 = 1.0e-2_dp
  !! numerical convergence constant
  real(kind=dp), parameter, public    :: eps5 = 1.0e-5_dp
  !! numerical convergence constant
  real(kind=dp), parameter, public    :: eps6 = 1.0e-6_dp
  !! numerical convergence constant
  real(kind=dp), parameter, public    :: eps7 = 1.0e-7_dp
  !! numerical convergence constant
  real(kind=dp), parameter, public    :: eps8 = 1.0e-8_dp
  !! numerical convergence constant
  real(kind=dp), parameter, public    :: eps10 = 1.0e-10_dp
  !! numerical convergence constant
  real(kind=dp), parameter, public    :: smearing_cutoff = 10._dp
  !! Cutoff for the smearing functions
  real(kind=dp), parameter, public    :: min_smearing_binwidth_ratio = 2._dp
  !! Don't smear but simply add the contribution to the
  !! relevant bin if the smearing/binwidth ratio is smaller than this value

  !~~ PHYSICAL CONSTANTS ~~!
  !
  ! Values of the fundamental constants taken from
  ! http://physics.nist.gov/cuu/Constants/index.html
  !
!~ Pick up default value; unfortunately, it doesn't work with indentation...
#ifndef CODATA2022
#ifndef CODATA2018
#ifndef CODATA2006
#ifndef CODATA2010
#define CODATA2022
#endif
#endif
#endif
#endif

! We don't check for multiply-defined flags: if it is the case, the code will not
! compile because of multiple definitions of the same flags

#ifdef CODATA2022
! ##### CODATA 2022 ##### !
!#warning "WANNIER90 INFO: Using CODATA 2022 constant values"
  real(kind=dp), parameter :: elem_charge_SI = 1.602176634e-19_dp   ! C
  !! e
  real(kind=dp), parameter :: elec_mass_SI = 9.1093837139e-31_dp    ! kg
  !! $$m_e$$
  real(kind=dp), parameter :: hbar_SI = 1.054571817e-34_dp          ! J * s
  !! $$\hbar$$
  real(kind=dp), parameter :: k_B_SI = 1.380649e-23_dp              ! J / K
  !! $$k_B$$
  real(kind=dp), parameter :: bohr_magn_SI = 927.40100657e-26_dp      ! J / T
  !! $$\mu_B$$
  real(kind=dp), parameter :: eps0_SI = 8.85418781887e-12_dp          ! F / m
  !! $$\epsilon_0$$
  real(kind=dp), parameter :: speedlight_SI = 299792458.0_dp        ! m / s
  !! $$c$$
  real(kind=dp), parameter :: eV_au = 3.6749322175665e-2_dp              ! (see table of Conv. Factors)
  !! eV in atomic units
  real(kind=dp), parameter :: eV_seconds = 6.582119569e-16_dp
  !! Electron Volt in seconds
  real(kind=dp), parameter :: bohr_angstrom_internal = 0.529177210544_dp
  !! Bohr to $$\AA$$
  ! Leave the length to this value, and don't exceed in length (needed for output formatting)
  character(len=75), parameter :: constants_version_str1 = "-> Using CODATA 2022 constant values"
  character(len=75), parameter :: constants_version_str2 = "   (http://physics.nist.gov/cuu/Constants/index.html)"
#endif

#ifdef CODATA2018
! ##### CODATA 2018 ##### !
!#warning "WANNIER90 INFO: Using CODATA 2018 constant values"
  real(kind=dp), parameter :: elem_charge_SI = 1.602176634e-19_dp   ! C
  !! e
  real(kind=dp), parameter :: elec_mass_SI = 9.1093837015e-31_dp    ! kg
  !! $$m_e$$
  real(kind=dp), parameter :: hbar_SI = 1.054571817e-34_dp          ! J * s
  !! $$\hbar$$
  real(kind=dp), parameter :: k_B_SI = 1.380649e-23_dp              ! J / K
  !! $$k_B$$
  real(kind=dp), parameter :: bohr_magn_SI = 927.40100783e-26_dp      ! J / T
  !! $$\mu_B$$
  real(kind=dp), parameter :: eps0_SI = 8.8541878128e-12_dp          ! F / m
  !! $$\epsilon_0$$
  real(kind=dp), parameter :: speedlight_SI = 299792458.0_dp        ! m / s
  !! $$c$$
  real(kind=dp), parameter :: eV_au = 3.6749322175655e-2_dp              ! (see table of Conv. Factors)
  !! eV in atomic units
  real(kind=dp), parameter :: eV_seconds = 6.582119569e-16_dp
  !! Electron Volt in seconds
  real(kind=dp), parameter :: bohr_angstrom_internal = 0.529177210903_dp
  !! Bohr to $$\AA$$
  ! Leave the length to this value, and don't exceed in length (needed for output formatting)
  character(len=75), parameter :: constants_version_str1 = "-> Using CODATA 2018 constant values"
  character(len=75), parameter :: constants_version_str2 = "   (http://physics.nist.gov/cuu/Constants/index.html)"
#endif

#ifdef CODATA2006
! ##### CODATA 2006 ##### !
!#warning "WANNIER90 INFO: Using CODATA 2006 constant values"
  real(kind=dp), parameter :: elem_charge_SI = 1.602176487e-19_dp   ! C
  !! e
  real(kind=dp), parameter :: elec_mass_SI = 9.10938215e-31_dp      ! kg
  !! $$m_e$$
  real(kind=dp), parameter :: hbar_SI = 1.054571628e-34_dp          ! J * s
  !! $$\hbar$$
  real(kind=dp), parameter :: k_B_SI = 1.3806504e-23_dp             ! J / K
  !! $$k_B$$
  real(kind=dp), parameter :: bohr_magn_SI = 927.400915e-26_dp      ! J / T
  !! $$\mu_B$$
  real(kind=dp), parameter :: eps0_SI = 8.854187817e-12_dp          ! F / m
  !! $$\epsilon_0$$
  real(kind=dp), parameter :: speedlight_SI = 299792458.0_dp        ! m / s
  !! $$c$$
  real(kind=dp), parameter :: eV_au = 3.674932540e-2_dp              ! (see table of Conv. Factors)
  !! eV in atomic units
  real(kind=dp), parameter :: eV_seconds = 6.582119e-16_dp
  !! Electron Volt in seconds
  real(kind=dp), parameter :: bohr_angstrom_internal = 0.52917720859_dp
  !! Bohr to $$\AA$$
  ! Leave the length to this value, and don't exceed in length (needed for output formatting)
  character(len=75), parameter :: constants_version_str1 = "-> Using CODATA 2006 constant values"
  character(len=75), parameter :: constants_version_str2 = "   (http://physics.nist.gov/cuu/Constants/index.html)"
#endif

#ifdef CODATA2010
! ##### CODATA 2010 ##### !
!#warning "WANNIER90 INFO: Using CODATA 2010 constant values"
  real(kind=dp), parameter :: elem_charge_SI = 1.602176565e-19_dp
  !! elemental charge
  real(kind=dp), parameter :: elec_mass_SI = 9.10938291e-31_dp
  !! electron mass
  real(kind=dp), parameter :: hbar_SI = 1.054571726e-34_dp
  !! hbar
  real(kind=dp), parameter :: k_B_SI = 1.3806488e-23_dp
  !! Boltzman Constant
  real(kind=dp), parameter :: bohr_magn_SI = 927.400968e-26_dp
  !! Bohr magneton
  real(kind=dp), parameter :: eps0_SI = 8.854187817e-12_dp
  !! Vacuum Dielectric Constant
  real(kind=dp), parameter :: speedlight_SI = 299792458.0_dp
  !! Speed of light
  real(kind=dp), parameter :: eV_au = 3.674932379e-2_dp
  !! Electron Volt in atomic units
  real(kind=dp), parameter :: eV_seconds = 6.582119e-16_dp
  !! Electron Volt in seconds
  real(kind=dp), parameter :: bohr_angstrom_internal = 0.52917721092_dp
  !! Bohr to Anstrom Conversion factor
  ! Leave the length to this value, and don't exceed in length (needed for output formatting)
  character(len=75), parameter :: constants_version_str1 = "-> Using CODATA 2010 constant values"
  character(len=75), parameter :: constants_version_str2 = "   (http://physics.nist.gov/cuu/Constants/index.html)"
#endif

#ifdef USE_WANNIER90_V1_BOHR
!#warning "WANNIER90 INFO: Using WANNIER ver. 1 version of bohr"
  real(kind=dp), parameter :: bohr = 0.5291772108_dp
  ! Leave the length to this value, and don't exceed in length (needed for output formatting)
  character(len=75), parameter :: bohr_version_str = "-> Using Bohr value from Wannier90 ver. 1.x (DEPRECATED!)"
#else
!#warning "WANNIER90 INFO: Using CODATA version of bohr"
  real(kind=dp), parameter :: bohr = bohr_angstrom_internal
  ! Leave the length to this value, and don't exceed in length (needed for output formatting)
  character(len=75), parameter :: bohr_version_str = "-> Using Bohr value from CODATA"
#endif

  type w90_physical_constants_type
    real(kind=dp) :: bohr = bohr
    character(len=75) :: bohr_version_str = bohr_version_str
    character(len=75) :: constants_version_str1 = constants_version_str1
    character(len=75) :: constants_version_str2 = constants_version_str2
  end type w90_physical_constants_type

  type pw90_physical_constants_type
    real(kind=dp) :: elem_charge_SI = elem_charge_SI ! elemental charge
    real(kind=dp) :: elec_mass_SI = elec_mass_SI     ! electron mass
    real(kind=dp) :: hbar_SI = hbar_SI               ! hbar
    real(kind=dp) :: k_B_SI = k_B_SI                 ! Boltzman Constant
    real(kind=dp) :: eps0_SI = eps0_SI               ! Vacuum Dielectric Constant
    real(kind=dp) :: eV_au = eV_au                   ! Electron Volt in atomic units
    real(kind=dp) :: eV_seconds = eV_seconds         ! Electron Volt in seconds
    real(kind=dp) :: bohr = bohr
    character(len=75) :: bohr_version_str = bohr_version_str
    character(len=75) :: constants_version_str1 = constants_version_str1
    character(len=75) :: constants_version_str2 = constants_version_str2
  end type pw90_physical_constants_type

  public :: w90_physical_constants_type, pw90_physical_constants_type

end module w90_constants