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.

WWW: https://github.com/MolSSI/QCElemental