celeritas::constants Namespace Reference

Mathematical, numerical, and physical constants. More...

Namespaces
namespace	codata2006
	Experimental physical constants from CODATA 2006.
namespace	codata2018
	Experimental physical constants from CODATA 2018.
namespace	codata2022
	Experimental physical constants from CODATA 2022.

Variables
constexpr Constant	a0_bohr = Constant{5.29177210903e-11} * units::meter
constexpr Constant	alpha_fine_structure = Constant{7.2973525693e-3}
constexpr Constant	atomic_mass = Constant{1.66053906660e-24} * units::gram
constexpr Constant	electron_mass = Constant{9.1093837015e-28} * units::gram
constexpr Constant	proton_mass = Constant{1.67262192369e-24} * units::gram
constexpr Constant	eps_electric
constexpr Constant	mu_magnetic
constexpr Constant	r_electron = Constant{2.8179403262e-15} * units::meter
constexpr Constant	rinf_rydberg = Constant{10973731.568160} / units::meter
constexpr Constant	eh_hartree = Constant{4.3597447222071e-18} / units::meter
constexpr Constant	lambdabar_electron = Constant{3.8615926796e-13} * units::meter
Physical constants with exact value as defined by SI
constexpr Constant	c_light = Constant{299792458.} * units::meter / units::second
constexpr Constant	h_planck = Constant{6.62607015e-34} * units::joule * units::second
constexpr Constant	e_electron = Constant{1.602176634e-19} * units::coulomb
constexpr Constant	k_boltzmann = Constant{1.380649e-23} * units::joule / units::kelvin
constexpr Constant	na_avogadro {6.02214076e23}
constexpr Constant	kcd_luminous {683}
Exact derivative constants
constexpr Constant	hbar_planck {h_planck / (2 * pi)}
Other constants with physical meaning
constexpr int	stable_decay_constant {0}
Mathemetical constants (truncated)
constexpr Constant	pi {3.14159265358979323846}
constexpr Constant	sqrt_pi {1.77245385090551602730}
constexpr Constant	euler {2.71828182845904523536}
constexpr Constant	sqrt_euler {1.64872127070012814685}
constexpr Constant	sqrt_two {1.41421356237309504880}
constexpr Constant	sqrt_three {1.73205080756887729353}

Detailed Description

Mathematical, numerical, and physical constants.

Some of the physical constants listed here are exact numerical values: see si-2019 for definition of constants and how they relate to the different units.

Celeritas	CLHEP	Notes
a0_bohr	Bohr_radius	Bohr radius
alpha_fine_structure	fine_structure_const
atomic_mass	amu	Not the same as 1/avogadro
eps_electric	epsilon0	Vacuum permittivity
h_planck	h_Planck
k_boltzmann	k_Boltzmann
mu_magnetic	mu0	Vacuum permeability
na_avogadro	Avogadro	[1/mol]
r_electron	classic_electr_radius	Classical electron radius
kcd_luminous	[none]	Lumens per Watt
lambdabar_electron	electron_Compton_length	Reduced Compton wavelength
stable_decay_constant	[none]	Decay for a stable particle

In the CLHEP unit system, the value of the constant e_electron is defined to be 1 and coulomb is derivative from that. To avoid floating point arithmetic issues that would lead to the "units" and "constants" having different values for it, a special case redefines the value for CLHEP.

Some experimental physical constants are derived from the other physical constants, but for consistency and clarity they are presented numerically with the units provided in the CODATA 2018 or 2022 datasets. The CELERITAS_CODATA cmake variable determines which of the two datasets is "inlined" into the celeritas namespace, allowing fine-grain transition for classes that require it. The Constants.test.cc unit tests compare the numerical value against the derivative values inside the celeritas unit system. All experimental values include the final (usually two) imprecise digits; their precision is usually on the order of \( 10^{-11} \).