For Bosons the occupation number is not restricted, so one must sum over
all integers in (C.12)
(C.16)
The logarithm of (C.16) yields the thermodynamic
potential
(C.17)
The mean number of particles is obtained from
by differentiating
with respect to the FERMI energy, as in (C.5), by keeping
and (equivalently the ) fixed. As a result, the mean number
of Bosons is given by the Bose-EINSTEIN distribution function
(C.18)
where is the mean occupation number in the th state.