Notes about the IGLO family
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These basis sets are intended for computing NMR chemical shifts.
IGLO - Individual Gauge for Localized Orbitals

According to Fouda2017a, these were built upon old huzinaga basis sets and my not be optimal for
all calculations. They are often used for the of magnetic properties; however, they
have only been defined for hydrogen and the first- and second-row p-block elements.
IGLO-II and IGLO-III basis sets are only available for the p-block elements.

For the p-block elements, the IGLO-II basis set has a much lower error (<0.9 eV) than basis sets
of comparable size. It is difficult to understand in detail the reason for the excellent performance
of the IGLO-II basis set since it may be a consequence of a balance between several different factors.
One notable difference between the IGLO-II basis set and 6-31G(d,p) is that the exponents of the
Gaussian functions of the inner 1s orbital are larger in IGLO-II. If H  2 S is taken as an example,
the CEBE is computed to be 2485.0 eV with 6-31G(d,p) and 2468.9 eV with IGLO-II compared with a value
of 2470.3 eV for pcSseg-4, consistent with the better performance of IGLO-II.
The IGLO-III basis set also performs well, but it is surprising that IGLO-III shows no improvement over IGLO-II.≈ß