constants
- qcelemental.constants = <qcelemental.physical_constants.context.PhysicalConstantsContext object>
- CODATA physical constants set from NIST. - Parameters:
- context (str) – {‘CODATA2014’, ‘CODATA2018’} Origin of loaded data. 
 - qcelemental.pc
- Each physical constant is an entry in pc, where key is the lowercased string of the NIST name (or any alias) and the value is a Datum object with lbl the exact NIST name string, units, data value as Decimal object, and any uncertainty in the comment field.