# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at https://mozilla.org/MPL/2.0/.
from __future__ import annotations
"""
Physical constants
==================
Module containing a pre-set set of physical constants. The SI units are following the *new* convention
that takes effect on 20 May 2019.
The currently stored constants are (all are given in SI units):
PhysicalConstant
q
c
h
hbar
m_e
m_p
G0
G
All constants may be used like an ordinary float (which converts it to a float):
>>> c
299792458.0 m/s
>>> c * 2
599584916
while one can just as easily convert the units (which ensures thay stay like another `PhysicalConstant`):
>>> c('Ang/ps')
2997924.58 Ang/ps
"""
from ._internal import set_module
from .unit.base import units
__all__ = ["PhysicalConstant"]
@set_module("sisl")
class PhysicalConstant(float):
"""Class to create a physical constant with unit-conversion capability, works exactly like a float.
To change the units simply call it like a method with the desired unit:
>>> m = PhysicalConstant(1., 'm')
>>> m.unit
'm'
>>> m2nm = m('nm')
>>> m2nm
1000000000.0 nm
>>> m2nm.unit
'nm'
>>> m2nm * 2
1000000000.0
"""
__slots__ = ["_unit"]
def __new__(cls, value, unit):
constant = float.__new__(cls, value)
return constant
[docs]
def __init__(self, value, unit):
self._unit = unit
@property
def unit(self):
"""Unit of constant"""
return self._unit
def __str__(self):
return "{} {}".format(float(self), self.unit)
[docs]
def __call__(self, unit=None):
"""Return the value for the constant in the given unit, otherwise will return the units in SI units"""
if unit is None:
return self
return PhysicalConstant(self * units(self.unit, unit), unit)
def __eq__(self, other):
if isinstance(other, PhysicalConstant):
super().__eq__(self, other * units(other.unit, self.unit))
return super().__eq__(self, other)
__all__ += ["q", "c", "h", "hbar", "m_e", "m_p", "G", "G0", "a0"]
# These are CODATA-2018 values
#: Unit of charge [C]
q = PhysicalConstant(1.602176634e-19, "C")
#: Bohr radius [m]
a0 = PhysicalConstant(5.29177210903e-11, "m")
#: Boltzmann constant [J K^-1]
kB = PhysicalConstant(1.380649e-23, "J/K")
#: Electron mass [kg]
m_e = PhysicalConstant(9.1093837015e-31, "kg")
#: Planck constant [J Hz^-1]
h = PhysicalConstant(6.62607015e-34, "J s")
#: Reduced Planck constant [J Hz^-1]
hbar = PhysicalConstant(1.0545718176461565e-34, "J s")
#: Proton mass [kg]
m_p = PhysicalConstant(1.67262192369e-27, "kg")
#: Speed of light in vacuum [m s^-1]
c = PhysicalConstant(299792458.0, "m/s")
# Values not found in the CODATA table
#: Conductance quantum [S], or [m^2/s^2]
G0 = PhysicalConstant(2 * (q**2 / h), "m^2/s^2")
#: Gravitational constant [m^3/kg/s^2]
G = PhysicalConstant(6.6740831e-11, "m^3/kg/s^2")