Notes about Pople basis sets
============================

There are a few types - 3-21G, 4-31G, 5-21G, 5-31G, 6-21G, 6-31G. Of
these, only 3-21G and the 6-31G subfamily are regularly used.

5-21G is only included in the original BSE due to Gaussian using it for
Li and B for the 4-31G basis set. I believe they are rarely used.

For hydrogen and helium, there is no split core/valence. Therefore,
4-31G, 5-31G, and 6-31G are all equivalent for H and He. These basis
sets are stored in the 31G-* files.

For beryllium, the 5-21G/6-31G basis sets given in dill1975a were
superseded by ones given in binkley1977a. The original data from dill1975a
is not included in the new BSE.

For 6-31G, the basis sets for potassium and calcium were originally
given in rassolov1998a, along with d-type polarization functions with an
exponent of 0.2000.  Rassolov2001a updates these basis sets, adding extra
d functions to the valence. In doing so, the d-type polarization functions
were also updated, to be 1/4 the smallest valence d function.  As far
as I know, the diffuse functions have not been updated.

There does not appear to be diffuse functions available for helium.

For Na-Ar (Z=11-18), 6-31G uses the same core as 6-21G (gordon1982a)
with a different valence (francl1982a).

For Li-Ne (Z=3-10), 3-21G uses the same valence as 6-21G (binkley1980a).

6-31G for helium/neon do not appear to be published. For v1, I have taken the data
from Gaussian 09.

In Gaussian, the added polarization function for He is the same as for H.
Neon uses the same as for C-F. The polarization functions for Li-B are of unknown
origin, but appear to be evenly-spaced.


Data sources
------------

v1 of the data comes from Gaussian09 and GAMESS. Both generally match the old BSE,
however it looks like GAUSSIAN as re-normalized contraction coefficients, so they
have more decimal places.

I have chosen GAMESS for the data for Ga-Kr, due to Gaussian using a different
basis set for Ga-Kr. See below for the reason.


Differences with Gaussian
-------------------------

Gaussian does not included the added d shell for K,Ca found in rassolov2001. I have added them
directly from the paper. The polarization functions for K,Ca that are in gaussian are of unknown
origin.

Gaussian choses a different basis set for Ga-Kr. They have chosen the basis sets
found in blaudeau1997a. This basis is not consistent with the typical terminology,
and therefore moved to 6-31G(C), as recommended in rassolov2001a.

The original BSE had the data for Ga-Kr, but only for the 6-31G*. The basis sets there
are consistent with my interpretation, and therefore differed from Gaussian.


3-21G basis
-----------

3-21G was developed later, and uses pieces of the Huzinaga MINI basis set for the
core and some valence.


Differences/Issues with the original BSE
----------------------------------------

The original BSE sometimes truncates to a fixed number of decimal places, removing
significant figures. 

In the original BSE, the H basis for 6-31G and 4-31G differ slightly,
possibly due to transcription error. The 6-31G basis set for H in
GAMESS and Gaussion both agree with the basis set given in 4-31G in the
original BSE.

The original BSE was missing the modified potassium and calcium given in rassolov2001a.
