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
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 email@example.com.