!-*- 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
