Source code for ase.units

"""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
    # http://dx.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
    # http://dx.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
    # http://dx.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
    # http://dx.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}}


[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['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, Ry, Rydberg) = [0.0] * 43 # Now update the module scope: globals().update(create_units(__codata_version__))