According to Wikipedia: Functional forms and parameter sets have been defined by the developers of interatomic potentials and feature variable degrees of self-consistency and transferability. When functional forms of the potential terms vary, the parameters from one interatomic potential functio...

For hydrogen, the 3-21G basis set (in CFOUR format) is H:3-21G 3-21G Split-valence basis set 1 0 2 3 0.5447178000D+01 0.8245472400D+00 0.1831915800D+00 0.1562849787D+00 0.00000000 0.9046908767D+00 0.00000000 0.00000000 1.0000000 My interpretation is that this defines two orb...