50 Gases: the density ofstates
States are uniformly distributedink-space, thatisthedensityofstatesink-space
is constant, depending only on the box volumeV.
Therefore a grouping ofstates, neededtodefine a sensibledistribution, is
convenientlyrelatedto volumeink-space.
Similar ideas are used to describe gases in situations of restricted dimensions
(quantum sheets or wires).
Quantum states are specified bytheirk-spaceproperties,but also canhave addi-
tional specifications because of spin or polarisation, introducing a further factor
(Gin (4.5)).
The densityof states in energyplays an important role in thermal properties, and
is worked out from thek-space ideas together with the appropriate dispersion
(energy-momentum) relation.