The correlation term is related to the function,

where we have , , .
The parameters , *b*, and *c*, given in the table below,
are used to create three instances of *F*, using the table below.

The correlation energy is given by

The paramagnetic correlation energy is given by with the four parameters taken from the ``Paramagnetic'' line in the table. (Similar definitions hold for and .) The polarization contribution is given by

with the function *f* as defined above,
and where we have

and

is the difference of the ferromagnetic and paramagnetic correlation energies.

The exchange-correlation potential is given by

We use this form in all of the codes in this study.
To avoid undetected code bugs,
the associated subroutine was recoded independently
for one of the codes,
although the other three codes shared a common
subroutine. This subroutine will be provided upon request to
`clark@bruce.nist.gov`.