  The cluster expansion method is applied to electronic excitations and a set
of effective cluster density of states (ECDOS) are defined, analogous to
effective cluster interactions (ECI). The ECDOS are used to generate alloy
thermodynamic properties as well as equation of state (EOS) of electronic
excitations for the fcc Ni-Al systems. When parent clusters with small size,
the convergence of the expansion is not so good but the electronic density of
state (DOS) is well reproduced. However, the integrals of the DOS such as the
cluster expanded free energy, entropy and internal energy associated with
electronic excitations are well described at the level of the
tetrahedron-octahedron cluster approximation, indicating the ECDOS is
applicable to produce electronic ECI for cluster variation method or Monte
Carlo calculations. On the other hand, the Gruneisen parameter, calculated with
first-principles methods, is not any longer a constant and implies that the
whole DOS profile should be considered for EOS of electronic excitations, where
ECDOS adapts very well for disordered alloys and solid solutions.
