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Periodic table, physical constants, and molecule parsing for quantum chemistry.
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QCElemental is a resource module for quantum chemistry containing physical constants and periodic table data from NIST and molecule handlers.

Periodic Table and Physical Constants data are pulled from NIST srd144 and srd121, respectively (details) in a renewable manner (class around NIST-published JSON file).

This project also contains a generator, validator, and translator for Molecule QCSchema.

Periodic Table

A variety of periodic table quantities are available using virtually any alias:

>>> import qcelemental as qcel
>>> qcel.periodictable.to_E('KRYPTON')
>>> qcel.periodictable.to_element(36)
>>> qcel.periodictable.to_Z('kr84')
>>> qcel.periodictable.to_A('Kr')
>>> qcel.periodictable.to_A('D')
>>> qcel.periodictable.to_mass('kr', return_decimal=True)
>>> qcel.periodictable.to_mass('kr84')
>>> qcel.periodictable.to_mass('Kr86')

Physical Constants

Physical constants can be acquired directly from the NIST CODATA:

>>> import qcelemental as qcel
>>> qcel.constants.Hartree_energy_in_eV
>>> qcel.constants.get('hartree ENERGY in ev')
>>> pc = qcel.constants.get('hartree ENERGY in ev', return_tuple=True)
>>> pc.lbl
'Hartree energy in eV'
>>> pc.units
>>> pc.comment
'uncertainty=0.000 000 17'

Alternatively, with the use of the Pint unit conversion package, arbitrary conversion factors can be obtained:

>>> qcel.constants.conversion_factor("bohr", "miles")

Covalent Radii

Covalent radii are accessible for most of the periodic table from Alvarez, Dalton Transactions (2008) doi:10.1039/b801115j.

>>> import qcelemental as qcel
>>> qcel.covalentradii.get('I')
>>> qcel.covalentradii.get('I', units='angstrom')
>>> qcel.covalentradii.get(116)
Traceback (most recent call last):
qcelemental.exceptions.DataUnavailableError: ('covalent radius', 'Lv')
>>> qcel.covalentradii.get(116, missing=4.0)
>>> qcel.covalentradii.get('iodine', return_tuple=True).to_dict()
{'label': 'I', 'units': 'angstrom', 'data': Decimal('1.39')}
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