"""ase.units
Physical constants and units derived from CODATA for converting
to and from ase internal units.
"""
from math import pi, sqrt
# the version we actually use
__codata_version__ = '2014'
# Instead of a plain dict, if the units are in the __dict__ of a
# dict subclass, they can be accessed as attributes in a similar way
# to a module.
class Units(dict):
"""Dictionary for units that supports .attribute access."""
def __init__(self, *args, **kwargs):
super(Units, self).__init__(*args, **kwargs)
self.__dict__ = self
# this is the hard-coded CODATA values
# all other units are dynamically derived from these values upon import of the
# module
CODATA = {
# the "original" CODATA version ase used ever since
# Constants from Konrad Hinsen's PhysicalQuantities module (1986 CODATA)
# Add the constant pi used to define the mu0 and hbar here for reference
# as well
'1986': {'_c': 299792458., # speed of light, m/s
'_mu0': 4.e-7 * pi, # permeability of vacuum
'_Grav': 6.67259e-11, # gravitational constant
'_hplanck': 6.6260755e-34, # Planck constant, J s
'_e': 1.60217733e-19, # elementary charge
'_me': 9.1093897e-31, # electron mass
'_mp': 1.6726231e-27, # proton mass
'_Nav': 6.0221367e23, # Avogadro number
'_k': 1.380658e-23, # Boltzmann constant, J/K
'_amu': 1.6605402e-27}, # atomic mass unit, kg
# CODATA 1998 taken from
# https://doi.org/10.1103/RevModPhys.72.351
'1998': {'_c': 299792458.,
'_mu0': 4.0e-7 * pi,
'_Grav': 6.673e-11,
'_hplanck': 6.62606876e-34,
'_e': 1.602176462e-19,
'_me': 9.10938188e-31,
'_mp': 1.67262158e-27,
'_Nav': 6.02214199e23,
'_k': 1.3806503e-23,
'_amu': 1.66053873e-27},
# CODATA 2002 taken from
# https://doi.org/10.1103/RevModPhys.77.1
'2002': {'_c': 299792458.,
'_mu0': 4.0e-7 * pi,
'_Grav': 6.6742e-11,
'_hplanck': 6.6260693e-34,
'_e': 1.60217653e-19,
'_me': 9.1093826e-31,
'_mp': 1.67262171e-27,
'_Nav': 6.0221415e23,
'_k': 1.3806505e-23,
'_amu': 1.66053886e-27},
# CODATA 2006 taken from
# https://doi.org/10.1103/RevModPhys.80.633
'2006': {'_c': 299792458.,
'_mu0': 4.0e-7 * pi,
'_Grav': 6.67428e-11,
'_hplanck': 6.62606896e-34,
'_e': 1.602176487e-19,
'_me': 9.10938215e-31,
'_mp': 1.672621637e-27,
'_Nav': 6.02214179e23,
'_k': 1.3806504e-23,
'_amu': 1.660538782e-27},
# CODATA 2010 taken from
# https://doi.org/10.1103/RevModPhys.84.1527
'2010': {'_c': 299792458.,
'_mu0': 4.0e-7 * pi,
'_Grav': 6.67384e-11,
'_hplanck': 6.62606957e-34,
'_e': 1.602176565e-19,
'_me': 9.10938291e-31,
'_mp': 1.672621777e-27,
'_Nav': 6.02214129e23,
'_k': 1.3806488e-23,
'_amu': 1.660538921e-27},
# CODATA 2014 taken from
# http://arxiv.org/pdf/1507.07956.pdf
'2014': {'_c': 299792458.,
'_mu0': 4.0e-7 * pi,
'_Grav': 6.67408e-11,
'_hplanck': 6.626070040e-34,
'_e': 1.6021766208e-19,
'_me': 9.10938356e-31,
'_mp': 1.672621898e-27,
'_Nav': 6.022140857e23,
'_k': 1.38064852e-23,
'_amu': 1.660539040e-27},
# CODATA 2018 taken from
# https://physics.nist.gov/cuu/Constants/index.html
'2018': {'_c': 299792458., # Exact
'_mu0': 4.0e-7 * pi, # Exact
'_Grav': 6.67430e-11, # +/- 0.000_15e-11
'_hplanck': 6.62607015e-34, # Exact
'_e': 1.602176634e-19, # Exact
'_me': 9.1093837015e-31, # +/- 0.000_000_0028e-31
'_mp': 1.67262192369e-27, # +/- 0.000_000_000_51e-27
'_Nav': 6.02214076e23, # Exact
'_k': 1.380649e-23, # Exact
'_amu': 1.66053906660e-27}, # +/- 0.000_000_000_50e-27
}
[docs]def create_units(codata_version):
"""
Function that creates a dictionary containing all units previously hard
coded in ase.units depending on a certain CODATA version. Note that
returned dict has attribute access it can be used in place of the module
or to update your local or global namespace.
Parameters:
codata_version: str
The CODATA version to be used. Implemented are
* '1986'
* '1998'
* '2002'
* '2006'
* '2010'
* '2014'
Returns:
units: dict
Dictionary that contains all formerly hard coded variables from
ase.units as key-value pairs. The dict supports attribute access.
Raises:
NotImplementedError
If the required CODATA version is not known.
"""
try:
u = Units(CODATA[codata_version])
except KeyError:
raise NotImplementedError('CODATA version "{0}" not implemented'
.format(codata_version))
# derived from the CODATA values
u['_eps0'] = (1 / u['_mu0'] / u['_c']**2) # permittivity of vacuum
u['_hbar'] = u['_hplanck'] / (2 * pi) # Planck constant / 2pi, J s
u['Ang'] = u['Angstrom'] = 1.0
u['nm'] = 10.0
u['Bohr'] = (4e10 * pi * u['_eps0'] * u['_hbar']**2 /
u['_me'] / u['_e']**2) # Bohr radius
u['eV'] = 1.0
u['Hartree'] = (u['_me'] * u['_e']**3 / 16 / pi**2 /
u['_eps0']**2 / u['_hbar']**2)
u['kJ'] = 1000.0 / u['_e']
u['kcal'] = 4.184 * u['kJ']
u['mol'] = u['_Nav']
u['Rydberg'] = 0.5 * u['Hartree']
u['Ry'] = u['Rydberg']
u['Ha'] = u['Hartree']
u['second'] = 1e10 * sqrt(u['_e'] / u['_amu'])
u['fs'] = 1e-15 * u['second']
u['kB'] = u['_k'] / u['_e'] # Boltzmann constant, eV/K
u['Pascal'] = (1 / u['_e']) / 1e30 # J/m^3
u['GPa'] = 1e9 * u['Pascal']
u['bar'] = 1e5 * u['Pascal']
u['Debye'] = 1.0 / 1e11 / u['_e'] / u['_c']
u['alpha'] = (u['_e']**2 / (4 * pi * u['_eps0']) /
u['_hbar'] / u['_c']) # fine structure constant
u['invcm'] = (100 * u['_c'] * u['_hplanck'] /
u['_e']) # cm^-1 energy unit
# Derived atomic units that have no assigned name:
# atomic unit of time, s:
u['_aut'] = u['_hbar'] / (u['alpha']**2 * u['_me'] * u['_c']**2)
# atomic unit of velocity, m/s:
u['_auv'] = u['_e']**2 / u['_hbar'] / (4 * pi * u['_eps0'])
# atomic unit of force, N:
u['_auf'] = u['alpha']**3 * u['_me']**2 * u['_c']**3 / u['_hbar']
# atomic unit of pressure, Pa:
u['_aup'] = u['alpha']**5 * u['_me']**4 * u['_c']**5 / u['_hbar']**3
u['AUT'] = u['second'] * u['_aut']
# SI units
u['m'] = 1e10 * u['Ang'] # metre
u['kg'] = 1. / u['_amu'] # kilogram
u['s'] = u['second'] # second
u['A'] = 1.0 / u['_e'] / u['s'] # ampere
# derived
u['J'] = u['kJ'] / 1000 # Joule = kg * m**2 / s**2
u['C'] = 1.0 / u['_e'] # Coulomb = A * s
return u
# Define all the expected symbols with dummy values so that introspection
# will know that they exist when the module is imported, even though their
# values are immediately overwritten.
# pylint: disable=invalid-name
(_Grav, _Nav, _amu, _auf, _aup, _aut, _auv, _c, _e, _eps0,
_hbar, _hplanck, _k, _me, _mp, _mu0, alpha, eV, fs, invcm,
kB, kJ, kcal, kg, m, mol, nm, s, second, A, AUT, Ang, Angstrom,
Bohr, C, Debye, GPa, Ha, Hartree, J, Pascal, bar, Ry, Rydberg) = [0.0] * 44
# Now update the module scope:
globals().update(create_units(__codata_version__))