Split valence-shell basis set

The 4-3IG basis set is not exactly a double zeta basis since only the valence functions are doubled and a single function is still used for each inner shell orbital. It may be termed a split valence shell basis set. The inner shells contribute little to most chemical properties and usually vary only slightly from molecule to molecule. Not splitting the inner shell functions has some effect on the total energy, but little effect on dipole moments, valence ionization potentials, charge densities, dissociation energies, and most other calculated quantities of chemical interest. The 4-3IG basis thus consists of 2 functions for H and He, 9 functions for Li to Ne, 13 functions for Na to Ar,..., etc. For hydrogen the contractions are... 

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