constants.py

#!/usr/bin/env python3

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# RMG - Reaction Mechanism Generator                                          #
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r"""
The :mod:`molecule.constants` module contains module-level variables defining
relevant physical constants relevant in chemistry applications. The recommended
method of importing this module is ::

    import molecule.constants as constants

so as to not place the constants in the importing module's global namespace.

The constants defined in this module are listed in the table below:

.. table:: Physical constants defined in the :mod:`molecule.constants` module
    
    ======================= =================== =========================================================== ============================================================
    Symbol                  Constant            Value                                                       Description
    ======================= =================== =========================================================== ============================================================
    :math:`E_\mathrm{h}`    :data:`E_h`         :math:`4.35974434 \times 10^{-18} \ \mathrm{J}`             Hartree energy
    :math:`F`               :data:`F`           :math:`96485.3365 \ \mathrm{C/mol}`                         Faraday constant
    :math:`G`               :data:`G`           :math:`6.67384 \times 10^{-11} \ \mathrm{m^3/kg \cdot s^2}` Newtonian gravitational constant
    :math:`N_\mathrm{A}`    :data:`Na`          :math:`6.02214179 \times 10^{23} \ \mathrm{mol^{-1}}`       Avogadro constant
    :math:`R`               :data:`R`           :math:`8.314472 \ \mathrm{J/mol \cdot K}`                   gas law constant
    :math:`a_0`             :data:`a0`          :math:`5.2917721092 \times 10^{-11} \ \mathrm{m}`           Bohr radius
    :math:`c`               :data:`c`           :math:`299792458 \ \mathrm{m/s}`                            speed of light in a vacuum
    :math:`e`               :data:`e`           :math:`1.602176565 \times 10^{-19} \ \mathrm{C}`            elementary charge
    :math:`g`               :data:`g`           :math:`9.80665 \ \mathrm{m/s^2}`                            standard acceleration due to gravity
    :math:`h`               :data:`h`           :math:`6.62606896 \times 10^{-34} \ \mathrm{J \cdot s}`     Planck constant
    :math:`\hbar`           :data:`hbar`        :math:`1.054571726 \times 10^{-34} \ \mathrm{J \cdot s}`    reduced Planck constant
    :math:`k_\mathrm{B}`    :data:`kB`          :math:`1.3806504 \times 10^{-23} \ \mathrm{J/K}`            Boltzmann constant
    :math:`m_\mathrm{e}`    :data:`m_e`         :math:`9.10938291 \times 10^{-31} \ \mathrm{kg}`            electron rest mass
    :math:`m_\mathrm{n}`    :data:`m_n`         :math:`1.674927351 \times 10^{-27} \ \mathrm{kg}`           neutron rest mass
    :math:`m_\mathrm{p}`    :data:`m_p`         :math:`1.672621777 \times 10^{-27} \ \mathrm{kg}`           proton rest mass
    :math:`m_\mathrm{u}`    :data:`amu`         :math:`1.660538921 \times 10^{-27} \ \mathrm{kg}`           atomic mass unit
    :math:`\pi`             :data:`pi`          :math:`3.14159 \ldots`      
    ======================= =================== =========================================================== ============================================================

"""

import math

################################################################################

#: The Hartree energy :math:`E_\mathrm{h}` in :math:`\mathrm{J}`
E_h = 4.35974434e-18

#: The Avogadro constant :math:`N_\mathrm{A}` in :math:`\mathrm{mol^{-1}}`       
Na = 6.02214179e23

#: The gas law constant :math:`R` in :math:`\mathrm{J/mol \cdot K}`
R = 8.314472

#: The Bohr radius :math:`a_0` in :math:`\mathrm{m}`
a0 = 5.2917721092e-11

#: The atomic mass unit in :math:`\mathrm{kg}`
amu = 1.660538921e-27

#: The speed of light in a vacuum :math:`c` in :math:`\mathrm{m/s}`
c = 299792458

#: The elementary charge :math:`e` in :math:`\mathrm{C}`
e = 1.602176565e-19

#: The Planck constant :math:`h` in :math:`\mathrm{J \cdot s}`
h = 6.62606896e-34

#: The reduced Planck constant :math:`\hbar` in :math:`\mathrm{J \cdot s}`
hbar = 1.054571726e-34

#: The Boltzmann constant :math:`k_\mathrm{B}` in :math:`\mathrm{J/K}`
kB = 1.3806504e-23

#: The mass of an electron :math:`m_\mathrm{e}` in :math:`\mathrm{kg}`
m_e = 9.10938291e-31

#: The mass of a neutron :math:`m_\mathrm{n}` in :math:`\mathrm{kg}`
m_n = 1.674927351e-27

#: The mass of a proton :math:`m_\mathrm{p}` in :math:`\mathrm{kg}`
m_p = 1.672621777e-27

#: :math:`\pi = 3.14159 \ldots`      
pi = float(math.pi)

#: Faradays Constant F in C/mol
F = 96485.3321233100184

#: Vacuum permittivity 
epsilon_0 = 8.8541878128

################################################################################

# Cython does not automatically place module-level variables into the module
# symbol table when in compiled mode, so we must do this manually so that we
# can use the constants from both Cython and regular Python code
globals().update({
    'E_h': E_h,
    'Na': Na,
    'R': R,
    'a0': a0,
    'amu': amu,
    'c': c,
    'e': e,
    'h': h,
    'hbar': hbar,
    'kB': kB,
    'm_e': m_e,
    'm_n': m_n,
    'm_p': m_p,
    'pi': pi,
    'F': F,
    'epsilon_0': epsilon_0,
})