physical_constants

This module provides some physical constants and conversions for convenience. These constants are taken from CODATA 2018 [https://doi.org/10.1103/RevModPhys.93.025010]. The main purpose of this module is to facilitate comparison of FEASST results to machine percision. For example, the molar gas constant is derived from the Boltzmann and Avogadro constants. However, their product to machine percision does not match scipy.constants.physical_constants[“molar gas constant”]. And the conversion of elementary charge per distance to energy units can be even more problematic. Please do not use this as a primary source for NIST physical constants. Instead, verify them with CODATA sources.

class physical_constants.ElementaryCharge

The elementary charge.

units()

Return the units.

>>> from pyfeasst import physical_constants
>>> physical_constants.ElementaryCharge().units()
'C'

value()

Return the value.

>>> from pyfeasst import physical_constants
>>> physical_constants.ElementaryCharge().value()
1.602176634e-19

class physical_constants.BoltzmannConstant

The Boltzmann constant.

units()

Return the units.

>>> from pyfeasst import physical_constants
>>> physical_constants.BoltzmannConstant().units()
'J K^-1'

value()

Return the value.

>>> from pyfeasst import physical_constants
>>> physical_constants.BoltzmannConstant().value()
1.380649e-23

class physical_constants.AvogadroConstant

The Avogadro constant.

units()

Return the units.

>>> from pyfeasst import physical_constants
>>> physical_constants.AvogadroConstant().units()
'mol^-1'

value()

Return the value.

>>> from pyfeasst import physical_constants
>>> physical_constants.AvogadroConstant().value()
6.02214076e+23

class physical_constants.VacuumElectricPermittivity

The vacuum electric permittivity.

units()

Return the units.

>>> from pyfeasst import physical_constants
>>> physical_constants.VacuumElectricPermittivity().units()
'C^2 J^-1 m^-1'

value()

Return the value.

>>> from pyfeasst import physical_constants
>>> physical_constants.VacuumElectricPermittivity().value()
8.8541878128e-12

class physical_constants.MolarGasConstant

The molar gas constant or ideal gas constant. This is equivalent to the product of the Boltzmann and Avogadro constants.

units()

Return the units.

>>> from pyfeasst import physical_constants
>>> physical_constants.MolarGasConstant().units()
'J mol^-1 K^-1'

value()

Return the value.

>>> from pyfeasst import physical_constants
>>> physical_constants.MolarGasConstant().value()
8.31446261815324

class physical_constants.ESqPerAngstromToKJPerMol

Convert e^2/Angstrom to kJ/mol by a factor of units (kJ*A/e^2/mol). This is ElementaryCharge**2/(4*PI*VacuumElectricPermittivity*1e3/1e10/AvogadroConstant).

units()

Return the units.

>>> from pyfeasst import physical_constants
>>> physical_constants.ESqPerAngstromToKJPerMol().units()
'kJ A e^-2 mol^-1'

value()

Return the value.

>>> from pyfeasst import physical_constants
>>> physical_constants.ESqPerAngstromToKJPerMol().value()
1389.35457644382